CALIFORNIA AGRICULTURAL EXPERIMENT STATION 
 
 C I R C U L.A'R 3 4 7 
 Revised January 1950 
 
 The Water-Culture 
 Method for Growing 
 Plants without Soil 
 
 D. R. HOAGLAND and 
 
 D. I. ARNON 
 
 Revised by D. I. ARNON 
 
 — — 
 
 THIS EDITION includes a discussion 
 of general principles underlying 
 the use of ALL methods for growing 
 plants without soil. 
 
 THE COLLEGE OF AGRICULTURE 
 
 UNIVERSITY OF CALIFORNIA 
 
 BERKELEY 
 
ntttriCUlttttC is an all-inclusive term for the several methods of grow- 
 ing plants in artificial media— water culture, aggregate culture, and the 
 "adsorbed" nutrient technique. 
 
 *=£? Most claims for the advantages of nutriculture are unfounded. 
 
 < §Z It is not a new method for growing plants. 
 
 ^Z Anyone who uses it must have a knowledge of plant physiology. 
 
 "§Z Its commercial application is justifiable under very limited conditions 
 and only under expert supervision. 
 
 <£? Nutriculture is rarely superior to soil culture: 
 
 Yields are not strikingly different under comparable conditions. 
 
 Plants cannot be spaced closer than in a rich soil. 
 
 Plant growth habits are not changed by nutriculture. 
 
 Water requirement is no less in nutriculture. 
 
 Nutritional quality of the product is the same. 
 
 Nutrient deficiencies, insect attacks, and diseases present similar problems. 
 
 Climatic requirements are the same. 
 
 Favorable air temperatures are just as necessary as in soil. 
 
 -U -U -& 
 
 If, realizing these limitations, you still wish to experiment with nutri- 
 culture methods, you will find directions beginning on page 23. 
 
 Type of container 23 
 
 Nature of bed 24 
 
 Aeration of the root system 26 
 
 Planting procedures 27 
 
 Managing the solutions 27 
 
 Selecting the nutrient solution 29 
 
 Preparing the nutrient solution 29 
 
 Nutrient solutions for demonstrating mineral deficiencies 
 
 in plants 31 
 
Foreword 
 
 For over three decades, the California 
 Agricultural Experiment Station has con- 
 ducted investigations of problems of plant 
 nutrition with the use of water-culture 
 technique for growing plants, as one im- 
 portant method of experimentation. The 
 objective has been to gain a better under- 
 standing of fundamental factors which 
 govern plant growth, in order to deal 
 more effectively with the many complex 
 questions of soil and plant interrelations 
 arising in the field. Many workers have 
 participated in these investigations. One 
 of them, Dr. W. F. Gericke, conceived the 
 idea some time ago that the water-culture 
 method, hitherto employed only for scien- 
 tific studies, might be adapted to commer- 
 cial use, and proceeded to devise special 
 technique for this purpose. 
 
 In the nineteen thirties, this develop- 
 ment was given widespread publicity in 
 newspapers, Sunday supplements, and 
 popular journals. The possibility of 
 growing plants in a medium other than 
 soil intrigued many persons, and soon 
 extravagant claims were being made by 
 many of the most ardent proponents of 
 the commercial use of the water-culture 
 method. Furthermore, amateur garden- 
 ers sought to make this method a new 
 hobby. Thousands of inquiries came to 
 the University of California for detailed 
 information for general application of the 
 water-culture method to commercial as 
 well as to amateur gardening. 
 
 Because of doubts expressed concern- 
 ing many claims made for the use of the 
 water-culture method as a means of crop 
 
 production, it became evident that an in- 
 dependent appraisal of this method of 
 growing crops was highly desirable. I 
 therefore requested Professors D. R. 
 Hoagland and D. I. Arnon to conduct cer- 
 tain additional investigations and to pre- 
 pare a manuscript for a popular circular 
 on the general subject of growing plants 
 in nutrient solutions. 
 
 When this circular was first published 
 in 1938, neither the California Agricul- 
 tural Experiment Station nor the authors 
 made any general recommendations as to 
 the use of soilless culture methods for 
 commercial crop production. The pur- 
 pose of the publication was to make avail- 
 able such technical information from the 
 researches of the Station to those who 
 wished to experiment with the water- 
 culture method on their own responsibil- 
 ity. An attitude of caution and a balanced 
 consideration of the various factors de- 
 termining success in growing crops on a 
 large scale, whether in soil or in nutrient 
 solutions, was commended to the atten- 
 tion of those contemplating commercial 
 ventures. The purpose of this revised pub- 
 lication and the point of view of the Ex- 
 periment Station remain the same today. 
 The experience of the past decade, during 
 which a number of large-scale installa- 
 tions for soilless crop production was 
 established in the United States and over- 
 seas, fails to support the exaggerated 
 claims of the early enthusiasts of the 
 
 technique. 
 
 C. B. Hutchison 
 
 Vice-President of the University and 
 Dean of the College of Agriculture 
 
 [3] 
 
THE WATER-CULTURE METHOD 
 FOR GROWING PLANTS WITHOUT SOIL 
 
 D. R. Hoagland and D. I. Arnon 
 Revised by D. I. Arnon 2 
 
 Nutriculture is the term applied to all 
 methods for growing plants in a medium 
 other than natural soil. It includes water 
 culture, aggregate culture, and the "ad- 
 sorbed-nutrient" technique, all of which 
 are discussed briefly in this circular. Spe- 
 cific directions, however, are given for 
 water culture only. 
 
 In the nineteen thirties, the popular 
 press gave an immense amount of pub- 
 licity to the subject of commercial or 
 amateur growing of crops in "water cul- 
 ture." This is a method of growing plants 
 with their roots in a solution containing 
 the mineral nutrients essential for plant 
 growth. The solution takes the place of 
 soil in supplying water and mineral nu- 
 trients to the plant. "Tray agriculture," 
 "tank farming," and "hydroponics," were 
 other names given to this same process. 
 Frequently, popular accounts left the im- 
 pression that a new discovery had been 
 made which would revolutionize present 
 methods of crop production. Indeed, some 
 predicted that in the future water culture 
 would supplant the use of soils for grow- 
 ing many crops and would thus produce 
 far-reaching social dislocations. 
 
 Extravagant claims for nutriculture 
 are unfounded 
 
 Promoters have made wholly un- 
 founded claims that a new "profession of 
 soilless farming" has been developed, af- 
 fording extraordinary opportunities for 
 investment of time and funds. They have 
 attempted to convince the public that a 
 short course of training will give prepara- 
 tion for entering this new "profession." 
 The impression has also been given that 
 the water-culture method offers an easy 
 means of raising food for household use. 
 
 Widely circulated rumors, claims, and 
 predictions about the water-culture pro- 
 duction of crops often had little more to 
 commend them than the author's unre- 
 strained imagination. Grossly inaccurate 
 in fact and misleading in implication, 
 most of these claims betrayed an igno- 
 rance of even the elementary principles of 
 plant physiology. For example, there have 
 been statements that in the future most 
 of the food needed by the occupants of a 
 great apartment building may be grown 
 on the roof, and that in large cities "sky- 
 scraper" farms may supply huge quanti- 
 ties of fresh fruit and vegetables. One 
 Sunday-supplement article contained an 
 illustration showing a housewife opening 
 a small closet off the kitchen and picking 
 tomatoes from vines growing in water 
 culture with the aid of electric lights. 
 There has even arisen a rumor that the 
 restaurants of a large chain in New York 
 City are growing their vegetables in base- 
 ments. Stories of this kind have gained 
 wide currency and have captured the im- 
 agination of many persons. 
 
 Many factors have doubtless contrib- 
 uted to arousing the surprisingly wide 
 interest in the water-culture method of 
 crop production. Current stress upon soil 
 conservation, with attendant emphasis 
 upon needless soil depletion and land 
 erosion, has made the public especially 
 receptive to new ideas relating to crop 
 production. Some people have been im- 
 pressed by the assumed social and eco- 
 nomic significance of the water-culture 
 method. Others, moved by the common 
 
 1 Professor of Plant Nutrition and Plant Phys- 
 iologist in the Experiment Station, deceased. 
 
 2 Associate Professor of Plant Nutrition and 
 Associate Plant Physiologist in the Experiment 
 Station. 
 
 [4] 
 
delight of mankind in growing plants, 
 even though the garden space is reduced 
 to a window sill, have sought directions to 
 enable them to try a novel technique of 
 plant culture. 
 
 The consequence of the discussion of 
 this method has been the creation of a 
 great public demand for more specific 
 information. Should this newly aroused 
 interest in plant growth lead to a greater 
 diffusion of the knowledge of certain 
 general principles of plant physiology, 
 the publicity regarding the water-culture 
 method of crop production may in the 
 long run have a beneficial effect. Growing 
 plants in water culture has been consid- 
 ered by some popular writers as a "mar- 
 vel of science." The growth of plants is 
 indeed marvelous, but not more so when 
 plants are grown in water culture than 
 when they are grown in soil. 
 
 The two entirely distinct lines of in- 
 vestigation at the California Agricultural 
 
 Experiment Station, in which the water- 
 culture technique is used, have sometimes 
 been confused in popular discussions. 
 One of these concerns methods of grow- 
 ing plants in water culture under natural 
 light; the other, the study of special scien- 
 tific problems of plant growth in con- 
 trolled chambers artificially illuminated. 
 At the present time there is no economic 
 possibility of growing commercial crops 
 solely under artificial illumination, even 
 if there were any reason for doing so. 
 
 At several other institutions, consider- 
 able attention has been devoted to a study 
 of the effect of supplementing daylight 
 with artificial light during some seasons 
 of the year, to control the flowering period 
 or to accelerate growth of certain kinds 
 of plants (particularly floral) in green- 
 houses. So far, this practice has been ap- 
 plied mainly to plants developed in soil 
 and has no essential relation to the water- 
 culture method of growing plants. 
 
 NUTRtCULWRE is not a new method 
 
 Curiously enough, the earliest recorded 
 experiment with water cultures was car- 
 ried out in search of a so-called "principle 
 of vegetation" in a day when so little was 
 known about the principles of plant nu- 
 trition that there was small chance of 
 profitable results from such an experi- 
 ment. Woodward (1699) grew spearmint 
 in several kinds of water : rain, river, and 
 conduit water, to which in one case he 
 added garden mold. He found that the 
 greatest increase in the weight of the 
 plant took place in the water containing 
 the greatest admixture of soil. He con- 
 cluded "That earth, and not water, is the 
 matter that constitutes vegetables." 
 
 Water-culture technique developed 
 from plant nutrition studies 
 
 The real development of the technique 
 of water culture took place over three- 
 quarters of a century ago. It came as a 
 logical result of the modern concepts of 
 plant nutrition. By the middle of the 
 
 nineteenth century, enough of the funda- 
 mental facts of plant physiology became 
 known and properly evaluated to enable 
 the botanists and chemists of that period 
 correctly to assign to soil the part it plays 
 in the nutrition of plants. They realized 
 that plants are made of chemical elements 
 obtained from three sources: air, water, 
 and soil, and that plants grow and in- 
 crease in size and weight by combining 
 these elements into various plant sub- 
 stances. 
 
 Water is, of course, always the main 
 component of growing plants. But the 
 major portion, usually about 90 per cent, 
 of the dry matter of most plants is made 
 up of three chemical elements: carbon, 
 oxygen, and hydrogen. Carbon comes 
 from the air, oxygen from the air and 
 water, and hydrogen from water. In addi- 
 tion to these three, plants contain other 
 elements, such as nitrogen, phosphorous, 
 potassium, and calcium, which they ob- 
 tain from the soil. The soil then supplies 
 
 [5] 
 
a large number of chemical elements, but 
 they constitute only a very small portion 
 of the plant. Yet the various elements that 
 occur in plants in comparatively small 
 amounts are just as essential to growth as 
 those which compose the bulk of plant 
 tissues. 
 
 The publication in 1840 of Liebig's 
 book on the application of organic chem- 
 istry to agriculture and physiology, 3 in 
 which these facts were ably and effec- 
 tively brought to the attention of plant 
 physiologists and chemists of that period, 
 served as a great stimulus for undertaking 
 experimental work in plant nutrition. 
 (Liebig, however, failed to understand 
 the role of soil as a source of nitrogen for 
 plants; and the fixation of atmospheric 
 nitrogen by bacteria was not then known. ) 
 
 Once it was recognized that the func- 
 tion of the soil in the economy of the 
 plant is to furnish certain chemical ele- 
 ments, as well as water, it was but natural 
 to attempt to supply these elements and 
 water independently of soil. The credit 
 for initiating exact experimentation in 
 this field belongs to the French chemist, 
 Jean Boussingault, who is regarded as 
 the founder of modern methods of con- 
 ducting experiments in vegetation. 
 
 Boussingault, who had begun his ex- 
 periments on plants even before 1840, 
 used insoluble artificial soils: sand, 
 quartz, and sugar charcoal, which he 
 watered with solutions of known com- 
 position. His results provided experi- 
 mental verification for the mineral theory 
 of plant nutrition as put forward by 
 Liebig, and were at once a demonstration 
 of the feasibility of growing plants in a 
 medium other than a "natural soil." 
 
 This method of growing plants in arti- 
 ficial insoluble soils was later improved 
 by Salm-Horstmar (1856-1860) and has 
 been used since, with technical improve- 
 ments, by many investigators. In recent 
 years, large-scale techniques have been 
 devised for growing plants for experi- 
 mental or commercial purposes in beds 
 of sand or other inert solid material. 
 
 Modern technique in water culture 
 originated about 1860 
 
 After they were successfully grown in 
 artificial culture media, it was but one 
 more step to dispense with any solid 
 medium and attempt to grow plants in 
 water to which were added the chemical 
 elements they were known to require. 
 This was successfully accomplished in 
 1860 by Sachs and about the same time 
 by Knop. To quote Sachs directly: 
 
 In the year 1860, I published the results of 
 experiments which demonstrated that land 
 plants are capable of absorbing their nutritive 
 matters out of watery solutions, without the aid 
 of soil, and that it is possible in this way not 
 only to maintain plants alive and growing for a 
 long time, as had long been known, but also to 
 bring about a vigorous increase of their organic 
 substance, and even the production of seed 
 capable of germination. 4 
 
 The original technique developed by 
 Sachs for growing plants in nutrient solu- 
 tions is still widely used, essentially un- 
 altered. He germinated the seed in 
 well-washed sawdust, until the plants 
 reached a size convenient for transplant- 
 ing. After carefully removing and wash- 
 ing the seedling, he fastened it into a 
 perforated cork, with the roots dipping 
 into the solution. The complete assembly 
 is shown in figure 1, which is a reproduc- 
 tion of Sachs' illustration. 
 
 Since the publication of Sachs' stand- 
 ard solution formula (table 1) for grow- 
 ing plants in water culture, many other 
 formulas have been used with success by 
 investigators in different countries. Knop, 
 who undertook water-culture experiments 
 at the same time as Sachs, proposed in 
 1865 a nutrient solution, which became 
 one of the most widely employed in 
 studies of plant nutrition. Other formulas 
 for nutrient solutions have been proposed 
 by Tollens in 1882, by Schimper in 1890, 
 by Pfeffer in 1900, by Crone in 1902, by 
 
 3 Liebig, Justus von. Chemistry in its applica- 
 tions to agriculture and physiology. [English 
 translation.] 401 pp. John Wiley, New York, 
 N.Y. 1861. 
 
 4 Sachs, Julius von. Lectures on the physiology 
 of plants. 836 pp. Clarendon Press, Oxford. 1887. 
 
 [6] 
 
Tottingham in 1914, by Shive in 1915, by 
 Hoagland in 1920, and by many others. 
 At the very beginning of the water- 
 culture work, investigators clearly recog- 
 nized that no one composition of a 
 nutrient solution is always superior to 
 
 Fig. 1. Water-culture 
 installation employed 
 by the plant physiologist 
 Sachs in the middle of 
 the last century. (Repro- 
 duced from Sachs, Lec- 
 tures on the Physiology 
 of Plants, Clarendon 
 Press. 1887.) 
 
 every other composition, but that within 
 certain ranges of composition and total 
 concentration, there could be fairly wide 
 latitude in the nutrient solutions suitable 
 for plant growth. Thus Sachs wrote: 
 
 I mention the quantities (of chemicals) I am 
 accustomed to use generally in water cultures, 
 with the remark, however, that a somewhat wide 
 margin may be permitted with respect to the 
 quantities of the individual salts and the con- 
 centration of the whole solution — it does not 
 matter if a little more or less of the one or the 
 other salt is taken — if only the nutritive mixture 
 is kept within certain limits as to quality and 
 quantity, which are established by experience. 
 
 Water culture was long used only 
 as research technique 
 
 Until recently, the water-culture tech- 
 nique was employed exclusively in small- 
 scale, controlled laboratory experiments 
 intended to solve fundamental problems 
 of plant nutrition and physiology. These 
 experiments have led to the determination 
 of the list of chemical elements essential 
 for plant life. They have thus profoundly 
 influenced the practice of soil manage- 
 ment and fertilization for purposes of 
 crop production. 5 In recent years, great 
 refinements in water-culture technique 
 have made possible the discovery of sev- 
 eral new essential elements. These, al- 
 though required by plants in exceedingly 
 small amounts, often are of definite prac- 
 tical importance in agricultural practice. 
 The elements derived from the nutrient 
 medium now considered to be indispen- 
 sable for the growth of higher green 
 plants are nitrogen, phosphorus, potas- 
 sium, sulfur, calcium, magnesium, iron, 
 boron, manganese, copper, and zinc. New 
 evidence suggests that molybdenum has 
 to be added to the list. 6 Present indica- 
 tions are that further refinements of tech- 
 nique may lead to the discovery of still 
 other elements essential in minute quan- 
 tity for growth. 
 
 In addition to the list of essential ele- 
 ments—obviously of first importance in 
 making artificial culture media for grow- 
 ing plants— a large amount of informa- 
 tion has been amassed on the desirable 
 proportions and concentrations of the 
 essential elements, and on such physical 
 and chemical properties of various cul- 
 ture solutions as acidity, alkalinity, and 
 osmotic characteristics. A most important 
 
 5 However, nutrient solutions such as are em- 
 ployed in water-culture experiments are not 
 applied directly to soils. For discussion of fer- 
 tilizer problems consult: Hoagland, D. R., 
 Fertilizers, soil analysis, and plant nutrition. 
 California Agr. Exp. Sta. Cir. 367: 1-24. Re- 
 vised, 1949. 
 
 6 Arnon, D. I., and P. R. Stout. Molybdenum 
 as an essential element for higher plants. Plant 
 Physiology 14: 599-602. 1939. 
 
 [7] 
 
recent development in the technique has 
 been the recognition of the importance, 
 for many plants, of special aeration of 
 the nutrient solution to supplement the 
 oxygen supply normally entering it when 
 in free contact with the surrounding at- 
 mosphere. 
 
 Present-day commercial water cul- 
 ture involves no new principles 
 
 The recently publicized use of the 
 water-culture technique for commercial 
 crop production rests on the same princi- 
 ples of plant nutrition as were discussed 
 above. It involves the application of a 
 large-scale technique, developed on the 
 basis of an understanding of plant nutri- 
 tion gained in previous investigations 
 conducted on a laboratory scale. The lat- 
 ter have provided knowledge of the com- 
 position of suitable culture solutions. 
 Furthermore, methods of controlling the 
 concentration of nutrients and the degree 
 of acidity are, except for modifications 
 imposed by the large scale of operations, 
 similar to those employed in small-scale 
 laboratory experiments. 
 
 The selection of a particular type of 
 covering for the tanks adapted to large- 
 scale water-culture operations and of 
 methods for supporting the plants de- 
 
 pends on the kind of plant. Potatoes, for 
 example, require a suitable bed in which 
 tubers can develop. This is usually a 
 porous one placed just above the level of 
 the solution. Tomatoes need adequate 
 support only for the aerial portion of the 
 stem, assuming that the roots are in a 
 favorable culture-solution medium, ade- 
 quately aerated, and with light excluded. 
 A porous bed may be convenient as a 
 means of facilitating aeration of the solu- 
 tion, as a heat insulator, or as a support 
 for the plant, but plays no indispensable 
 role. Aside from such considerations, the 
 choice of a covering is determined largely 
 by expense and convenience, provided the 
 materials used are not toxic to plants. 
 
 With any kind of covering for the 
 tanks, an adequate supply of air to the 
 roots must be provided. While the use of 
 a porous bed instead of a perforated cover 
 facilitates aeration of roots, the bed can 
 be dispensed with if provision is made to 
 bubble air through the nutrient solutions 
 (fig. 2) . Recent experiments have shown 
 that even with the use of a porous bed, 
 bubbling air through the solution may be 
 advantageous or, under some conditions, 
 indispensable. 
 
 As illustrations of some scientific prob- 
 lems of plant nutrition which have been 
 
 TABLE 1. — Composition of Nutrient Solutions Used by Early Investigators* t 
 
 Sachs' solution 
 (1860) 
 
 Knop's solution 
 (1865) 
 
 Pfeffer's solution 
 (1900) 
 
 Crone's solution 
 (1902) 
 
 Ingredient 
 
 Grams 
 
 per 1,000 cc 
 
 H2O 
 
 Ingredient 
 
 Grams 
 
 per 1,000 cc 
 
 H2O 
 
 Ingredient 
 
 Grams 
 
 per 1,000 cc 
 
 H2O 
 
 Ingredient 
 
 Grams 
 
 per 1,000 cc 
 
 H2O 
 
 KN0 3 
 
 1.00 
 
 Ca(N0 3 ) 2 
 
 0.8 
 
 Ca(N0 3 ) 2 
 
 0.8 
 
 KN0 3 
 
 1.00 
 
 Ca 3 (P0 4 ) 2 
 
 0.50 
 
 KN0 3 
 
 0.2 
 
 KN0 3 
 
 0.2 
 
 Ca 3 (P0 4 ) 2 
 
 0.25 
 
 MgS0 4 
 
 0.50 
 
 KH 2 P0 4 
 
 0.2 
 
 MgS0 4 
 
 0.2 
 
 MgS0 4 
 
 0.25 
 
 CaS0 4 
 
 0.50 
 
 MgS0 4 
 
 0.2 
 
 KH 2 P0 4 
 
 0.2 
 
 CaS0 4 
 
 0.25 
 
 NaCl 
 
 0.25 
 
 FeP0 4 
 
 Trace 
 
 KC1 
 
 0.2 
 
 FeP0 4 
 
 0.25 
 
 FeS0 4 
 
 Trace 
 
 
 
 FeCl 3 
 
 Small 
 amount 
 
 
 
 * These and other formulas are given in: Miller, E. C, Plant physiology, p. 195-97. McGraw-Hill Book Co., 
 New York, N. Y. 1931. 
 
 t For best results, these solutions should be supplemented with boron, manganese, zinc, copper, and 
 molybdenum; see discussion in the text, pp. 29-31. 
 
 [8] 
 
Fig. 2. The use of the water-culture technique 
 for studying the nutritional responses of lettuce 
 plants under controlled conditions. The indi- 
 vidual plants are supported in corks, which are 
 placed in holes drilled in the metal covers. The 
 glass and rubber tubes carry compressed air, 
 which is bubbled through the nutrient solution. 
 
 elucidated by the aid of the water-culture 
 method of experimentation, the effects of 
 aeration of the roots on plant growth are 
 shown in plate 1, A, and the foliage symp- 
 toms of deficiencies of mineral elements 
 required in large or minute quantity in 
 plate 1, B and plates 2 to 4. 
 
 Solid aggregate culture provides 
 anchorage for plant roots 
 
 In the water-culture technique the 
 roots of plants are submerged in a liquid 
 solution of plant nutrients. As in a soil, 
 the roots serve as the organs of absorp- 
 tion for water and nutrients; unlike in 
 soil, the roots provide no anchorage for 
 the aerial portions of the plant. Special 
 provisions, discussed later, are necessary 
 for supporting plants grown in water 
 culture. 
 
 Plants may be grown without soil, how- 
 ever, by other techniques, in which the 
 roots serve as organs of both absorption 
 and anchorage. Instead of in a liquid 
 
 medium, the plants are placed in some 
 solid inert aggregate, periodically irri- 
 gated by a synthetic nutrient solution. 
 Sand culture is the earliest example of 
 this technique. Its development paralleled 
 that of water culture, and it was used 
 by many investigators to study the same 
 types of scientific problems of plant nu- 
 trition as were discussed under water 
 culture above. 
 
 Several experiment stations in recent 
 years have developed techniques of ag- 
 gregate culture adapted to growing plants 
 on a large scale. Instead of sand, many of 
 these techniques make use of such coarser 
 aggregates as gravel, cinders, burned 
 shale (haydite), crushed granite, and 
 vermiculite. These aggregates are placed 
 in especially constructed beds to which 
 the nutrient solutions are supplied at 
 regular intervals. 
 
 Subirrigation is often used in ag- 
 gregate culture 
 
 With the coarser aggregates, the nu- 
 trient solution is generally supplied by 
 a subirrigation method rather than by 
 surface applications. Labor-saving, auto- 
 matic devices for supplying nutrient so- 
 lutions to the culture beds are usually a 
 feature of the subirrigation methods. A 
 detailed discussion of these procedures, 
 which is beyond the scope of this circular, 
 will be found in other publications. 7 
 
 (The California Agricultural Experi- 
 ment Station cannot provide copies of 
 these publications. Inquiries should be 
 made at the source.) 
 
 7 Withrow, R. B., and Alice P. Withrow. Nutri- 
 culture. Indiana (Purdue Univ.) Agric. Exp. 
 Sta. S. C. 328: 1-60. 1948. 
 
 Kiplinger, D. C, and Alex Laurie. Growing 
 ornamental greenhouse crops in gravel culture. 
 Ohio Agric. Exp. Sta. Research Bull. 679: 1-59. 
 1948. 
 
 Davidson, 0. W. Large-scale soilless culture 
 for plant research. Soil Science 62: 71-86. 1946. 
 
 Robbins, W. R. Growing plants in sand cul- 
 tures for experimental work. Soil Science 62: 
 3-22. 1946. 
 
 Shive, J. W., and W. R. Robbins. Methods of 
 growing plants in solution and sand cultures. 
 
 New Jersey Agric. Exp. Sta. Bull. 636. 
 
 [9] 
 
No new principles are used in com- 
 mercial "aggregate" culture 
 
 As with large-scale water culture, the 
 techniques for aggregates do not rest on 
 any newly discovered principles of plant 
 nutrition. They represent an application 
 of engineering and technical principles 
 to the construction of beds and the cir- 
 culation of the nutrient solution, with 
 economy and ease in construction and 
 operation as objectives. Ingenious as 
 these technical devices are, they cannot 
 assure success in growing plants to any 
 operator who does not have a sound 
 knowledge of the physiological and horti- 
 cultural principles involved in crop pro- 
 duction. These principles, which are the 
 same for water and aggregate culture, 
 will be referred to in subsequent sections 
 of this circular. 
 
 Adsorbed-nutrient technique does 
 use a different principle 
 
 With either aggregate or water culture, 
 the plant nutrients are supplied in a 
 chemical solution. The management of 
 this solution involves the technical prob- 
 lems of preparing, testing, and adjusting 
 the concentrations of the individual nu- 
 trients. 
 
 Under the sponsorship of the Army 
 Air Forces during World War II, the 
 possibility of using a large-scale nutrient- 
 culture technique which would have some 
 of the "fool-proof" aspects of growing 
 plants in a fertile soil was explored. In- 
 stead of supplying the plant nutrients in 
 repeated applications of nutrient so- 
 lutions, as is the practice in aggregate 
 culture, a different principle was used. 
 The plant nutrients were not furnished as 
 chemical salts but rather as "adsorbed 
 ions" on synthetic ion-exchange mate- 
 rials, in a manner similar to that in which 
 some plant nutrients are bound to col- 
 loids in natural soils. The "charged" ion- 
 exchange materials were then mixed with 
 sand prior to planting the crop. After the 
 plants were in, only applications of water 
 would be necessary to make growth pos- 
 sible. 
 
 These wartime experiments were prom- 
 ising but were discontinued as the war 
 ended, before the "adsorbed-nutrient" 
 technique had passed the experimental 
 stage. The information derived from these 
 experiments has been published, 8 but no 
 recommendations for commercial appli- 
 cation can be made by the Experiment 
 Station at this time. 
 
 PRtHCfPLiS AND APPLICATION OF NUTRICULTURE 
 
 A knowledge of plant physiology is 
 necessary 
 
 It should be stated at the outset that 
 there is no magic in nutriculture methods. 
 They provide only another means of sup- 
 plying mineral nutrients and water to 
 plants. The absorption of nutrients and 
 water accounts for only two of the physio- 
 logical processes of the plant. In order to 
 evaluate the possibilities and limitations 
 of any special technique for growing 
 plants, one has to understand the signifi- 
 cance of other interrelated processes, 
 especially photosynthesis, respiration, 
 transpiration, and reproduction. The 
 currently prominent interest in the appli- 
 
 cation of nutriculture techniques to crop 
 production makes it desirable to discuss 
 briefly the various factors which need to 
 be considered by those contemplating an 
 investment of time and funds in this field. 
 
 What is the justification for nutri- 
 culture in crop production? 
 
 l.The answer to this question is that 
 the method has certain possibilities in 
 
 8 Arnon, Daniel I., and Karl A. Grossenbacher. 
 Nutrient culture of crops with the use of syn- 
 thetic ion-exchange materials. Soil Science 63: 
 159-180. 1947. 
 
 Arnon, Daniel I., and William R. Meagher. 
 Factors influencing availability of plant nutri- 
 ents from synthetic ion-exchange materials. Soil 
 Science 64 : 213-221. 1947. 
 
 [10 
 
the growing of special high-priced crops, 
 particularly out of season in greenhouses, 
 in localities where good soil is not avail- 
 able, or when maintenance of highly 
 favorable soil conditions is found too 
 expensive. 
 
 Soil beds in greenhouses often become 
 infected with disease-producing organ- 
 isms, or toxic substances may accumu- 
 late. Installation of adequate equipment 
 for sterilizing soils and operation of the 
 equipment may require considerable ex- 
 pense. Also, maintenance of fertility in 
 the soil beds is often laborious and expen- 
 sive. On the other hand, a synthetic nutri- 
 ent medium, expertly supervised, can 
 serve as a continuously favorable source 
 of nutrients and water and, especially if 
 combined with automatic devices, can 
 bring about economies in labor. 
 
 2. Very favorable climates in some re- 
 gions may justify growing certain crops 
 out of doors in nutriculture. The possi- 
 bilities of nutriculture are not confined to 
 greenhouses. In regions highly favored 
 climatically and with a good water supply 
 available, but where soil conditions are 
 adverse, there may be reasons for grow- 
 ing crops outdoors by nutriculture tech- 
 niques. 
 
 A case in point was the gravel-culture 
 installation of the Army Air Forces on 
 Ascension Island in the South Atlantic, 
 toward the end of World War II. 9 This 
 tiny volcanic island located near the 
 equator has a climate characterized by 
 mild temperatures and low rainfall. Over 
 most of its area there is no agricultural 
 soil. Because of the extreme geographic 
 isolation and difficulties of supply, the 
 large military garrison placed there dur- 
 ing the war could be adequately provided 
 only with the essential dietary staples, 
 such as grains and meat and milk prod- 
 ucts. The supply of fruits and vegetables 
 was limited to canned, dried, or dehy- 
 drated items. The psychological sat- 
 isfactions from a supply of fresh salad 
 vegetables and the attendant benefits to 
 the morale and, in some cases, even to the 
 
 health of troops, were deemed important 
 enough to justify a determined effort to 
 provide such items as fresh tomatoes, let- 
 tuce, peppers, radishes, and cucumbers. 
 To supply these from outside sources was 
 not practical. To grow them on the island 
 by conventional methods in soil was not 
 feasible. An aggregate culture installa- 
 tion, using a local gravel, was therefore 
 authorized for the soilless production of 
 fresh salad crops. 
 
 A remarkable feature of the Ascension 
 Island installation was the use of dis- 
 tilled sea water in making the nutrient 
 solutions. Without this engineering feat 
 of providing by distillation the large 
 water requirements of the growing crops, 
 the project could not have been under- 
 taken. The nutriculture installation on 
 Ascension Island accomplished its mis- 
 sion. It stands out as an example of the 
 successful application of the principles 
 of plant physiology and engineering tech- 
 niques to the growing of crops in loca- 
 tions devoid of natural soils. 
 
 What are the drawbacks of com- 
 mercial nutriculture? 
 
 In the United States, nutriculture tech- 
 niques have found application in green- 
 houses in the production of floral and 
 vegetable crops, and outdoors, in such 
 climatically favorable areas as in Florida. 
 Of the various techniques, the aggregate 
 or gravel culture is the one most com- 
 monly used in commercial installations. 
 The commercial application of the nu- 
 triculture techniques has not been as 
 widespread as its most ardent followers 
 expected. As foreseen over a decade ago 
 in the first edition of this circular, two 
 factors have limited the displacement of 
 soil by nutriculture and will continue to 
 do so : first, economic considerations and 
 second, familiarity of commercial grow- 
 ers with the management of soils rather 
 than with nutriculture methods. 
 
 Nutriculture. War Department Technical 
 Manual TM 20-500. 
 
 [HI 
 
1 . Nutriculture is costly and needs expert 
 supervision. The initial financial invest- 
 ment in nutriculture facilities is high. The 
 automatic adjustment of many of the fac- 
 tors determining the nutrition of the plant 
 is found in a soil naturally fertile or in 
 one capable of being made so by a simple 
 treatment but is lacking in nutriculture 
 methods. 
 
 Expert supervision is generally neces- 
 sary to cope with technical difficulties 
 which may be met. Some of these are the 
 character of the water, adjustment of the 
 acidity of the nutrient solution, toxic sub- 
 stances from tanks or beds, uncertainty 
 as to time for replenishing salts in the 
 nutrient solution or for changing it. 
 
 To the average grower, crop pro- 
 duction in nutriculture is an unfamiliar 
 undertaking, involving problems not en- 
 countered in soil culture. On the other 
 hand, growing plants in soil is one of the 
 oldest occupations of mankind, with a 
 rich fund of accumulated experience to 
 draw upon for guidance. 
 
 In the absence of such special consid- 
 erations which, for example, justified the 
 operation of the Ascension Island installa- 
 tion by the Army Air Forces during the 
 war, commercial success is unlikely, un- 
 less the most careful consideration is 
 given to economic factors. What crops, if 
 any, could be profitably grown by nutri- 
 culture methods would depend on (1) the 
 value of the crop in the market served, 
 in relation to cost of production,— this 
 would include a large outlay for beds, ma- 
 terials, and other equipment— and (2) 
 special costs of expert supervision and 
 operation. 
 
 2. Nutriculture demands knowledge of 
 all factors of plant growth. Amateurs have 
 sometimes mistakenly assumed that nutri- 
 culture techniques can substitute for lack 
 of horticultural skill in growing crops 
 on a commercial scale. Indispensable to 
 profitable crop production by nutricul- 
 ture methods is a general knowledge of 
 plant varieties, habits of growth, climatic 
 adaptations, and pollination, and of the 
 
 control of disease and insects— in other 
 words, the same knowledge now needed 
 for successful crop production in soils. 
 
 Nutriculture does not solve prob- 
 lems of sanitation 
 
 In certain parts of the world, agricul- 
 tural soils are fertilized by human ex- 
 creta. Fresh vegetables from such areas, 
 if consumed raw, are sometimes carriers 
 of pathogenic organisms. It has been sug- 
 gested that such a hazard can be elimi- 
 nated by the use of outdoor nutriculture 
 techniques. This suggestion does not 
 seem to be supported by enough scientific 
 evidence. It is not clear, for example, that 
 outdoor installations will be protected 
 from contamination by particles of soil, 
 carried from adjoining infected areas by 
 wind or other agencies. Rigorous cleans- 
 ing of all vegetables to be consumed raw 
 is a safety measure in any case. It is also 
 possible that some suitable cleansing 
 agent can be devised for the disinfection 
 of soil-grown vegetables. Moreover, it has 
 not been demonstrated that the disinfec- 
 tion of selected local soil areas and the 
 subsequent careful management of them 
 are impractical or offer less health se- 
 curity than artificial culture techniques. 
 
 Wherever pathogenic organisms from 
 the soil are a problem, standards of sani- 
 tation are notoriously low. Handling vege- 
 tables to be eaten raw, therefore, always 
 constitutes a health hazard. Rigid sanita- 
 tion measures are necessary against this 
 source of infection, regardless of the 
 method by which the crop was grown. 
 
 Nutriculture is rarely superior to 
 soil culture 
 
 Yields are not strikingly different under 
 comparable conditions. The impression 
 conveyed by many of the popular discus- 
 sions of nutriculture methods is that much 
 more can be produced on a given surface 
 of nutrient solution than on an equivalent 
 surface soil, even under the best soil con- 
 ditions feasible to maintain. Often quoted 
 is the yield of tomato plants grown for a 
 
 [12] 
 
»'- ■%» s^* ^ 5*"* * - r 
 
 Fig. 3. Growth of tomato plants in fertile soil, in nutrient solution, and in pure silica 
 sand irrigated each day with nutrient solution. Fruit had been harvested for 7 weeks 
 prior to taking the photograph. All plants have made excellent growth and set large 
 amounts of fruit in all three media. The general cultural conditions— spacing, staking, 
 etc.— were the same. 
 
 twelve months' period in a greenhouse 
 water-culture experiment in Berkeley. 10 It 
 is compared with average yields of toma- 
 toes under ordinary field conditions; the 
 yield from the water-culture plants is 
 computed to be many times greater. But 
 closer analysis shows that mistaken in- 
 ferences may be drawn from this com- 
 
 parison. Predictions concerning yields in 
 large-scale production are of doubtful 
 validity when based on those obtained in 
 small-scale experiments under laboratory 
 control. In any event, there is little profit 
 
 10 Gericke, W. F. Crop Production without 
 soil. Nature 141 : 536-40. 1938. See also the 
 article cited in footnote 14, on page 19. 
 
 [13] 
 
in comparing an average yield from un- 
 slaked tomato plants, grown during a 
 limited season under all types of soil and 
 climatic conditions in the field, with that 
 from staked plants grown in the protec- 
 tion of a greenhouse for a full year. 
 
 Evidence has long been available that 
 yields of tomatoes grown in a greenhouse, 
 in soil, can far exceed those obtained in 
 the field. It is true that in one series of 
 outdoor experiments, the yields of toma- 
 toes under water-culture conditions were 
 reported to be much higher than under 
 ordinary field conditions; but again, the 
 general cultural treatment of the plants— 
 especially with regard to spacing and 
 staking— was so different that compari- 
 sons of yield do not mean very much. 
 
 Any real test of the relative capacities 
 of soil and nutriculture media for crop 
 production requires that the two types of 
 culture be carried on side by side, with 
 similar spacing of plants and with the 
 same cultural treatment otherwise. The 
 soil should be of suitable depth and have 
 its nutrient supplying power and physical 
 condition as favorable for plant growth 
 as possible. An experiment of this kind, 
 with the tomato as the test plant, has been 
 carried out in Berkeley. 11 Several conclu- 
 sions derived from it warrant emphasis. 
 The yield of tomatoes grown by the usual 
 tank-culture technique was larger than 
 any heretofore reported for this method. 
 That from the soil-grown plants, however, 
 was not markedly different (fig. 3) . When 
 the greenhouse yields of tomatoes from 
 either soil- or nutriculture-grown plants 
 were compared on an acre basis with av- 
 erage yields of field-grov;n tomatoes, the 
 greenhouse plants gave far greater yields. 
 Such comparisons, however, can have no 
 direct practical significance because of 
 the differences in climatic factors, cul- 
 tural practice, and length of season in the 
 greenhouse and in the open field. 
 
 In one California commercial green- 
 house, the yields of tomatoes grown in 
 soil equaled those obtained in a success- 
 ful commercial greenhouse using water 
 
 culture. In another greenhouse using soil, 
 the yields were larger. 
 
 The yield of potatoes grown in a bed of 
 peat soil in Berkeley was as large as any 
 heretofore reported as produced by the 
 water-culture method. 
 
 Plants cannot be spaced closer than in 
 a rich soil. The suggestion has sometimes 
 been advanced that plants can be grown 
 more closely spaced in nutrient solutions 
 than in soil, but no convincing evidence of 
 this has been given. In our experiments, 
 we were able to grow tomato plants as 
 close together in the soil as in the solu- 
 tion (fig. 3) . The density of stand giving 
 the highest yields would be determined by 
 the adequacy of the light received by the 
 plants, when growth is not limited by 
 the supply of nutrients or water derived 
 from either soil or nutrient solution. 
 Closeness of spacing under field condi- 
 tions is, of course, limited by practical 
 considerations involving cost of crop 
 production. This consideration of eco- 
 nomic factors and of the adequacy of 
 light does not justify the view that the 
 nutriculture medium is better adapted 
 than soil to growing several different 
 crops simultaneously in the same bed. 
 
 Plant growth habits are not changed by 
 nutriculture. Some published pictures of 
 tomato plants grown in nutriculture show 
 impressive height. This growth in length 
 of vines is frequently the subject of popu- 
 lar comment. As a matter of fact, the 
 ability of tomato vines to extend is char- 
 acteristic of the plant and is not peculiar 
 to the nutriculture method. Staked plants 
 grown for a sufficiently long period in a 
 fertile soil, under favorable light and 
 temperature conditions, can also reach a 
 great height and bear fruit at the upper 
 levels (fig. 4) . In commercial greenhouse 
 practice, growers usually "top" the vines. 
 Fruit developed at higher level is likely 
 to be of inferior quality and is relatively 
 
 "Arnon, D. L, and D. R. Hoagland. Crop 
 production in artificial culture solutions and in 
 soils with special reference to factors influencing 
 yields and absorption of inorganic nutrients. 
 Soil Science 50 : 463-485. 1940. 
 
 [14] 
 
•# ' \ 1*"* V -»' ""; ' V 
 
 
 mm ^ 
 
 f *if j ^M 
 
 11 
 
 Fig. 4. Under favorable conditions, tomato 
 plants can grow to a great height and bear 
 fruit over an extended period of time. This is 
 equally possible in soil, sand, and water-culture 
 media. The plants in the foreground were grown 
 in a bed of fertile soil. At the time of taking this 
 photograph, several days before the termina- 
 tion of the experiment, most of the fruit had 
 already been harvested. 
 
 expensive to produce because of both the 
 labor required to attach supports to the 
 vines and the inconvenience of harvest- 
 ing. Furthermore, it may become profit- 
 able to discontinue the tomato harvest 
 when prices become low in the summer 
 and to use the greenhouse space to plant 
 another crop for the winter harvest. 
 
 Land plants have become adapted to 
 growing in soils during their evolutionary 
 history. It is not reasonable, therefore, to 
 expect some extraordinary increase in 
 their potentialities for growth when an 
 artificial medium is substituted for soil. 
 If no toxic conditions are present and a 
 fully adequate supply of water, mineral 
 salts, and oxygen is provided to the root 
 system, either through an artificial nutri- 
 ent solution or a soil, then in the absence 
 of plant diseases and pests, the growth of 
 a plant is limited by its inherited consti- 
 tution and by climatic conditions. 
 
 Water requirement is no less in nutri- 
 culture. The view has sometimes been 
 advanced that the water requirement is 
 smaller in nutriculture than in soil. 
 Utilizing climatically favored desert re- 
 gions to produce crops by large-scale 
 nutriculture is one of the recent popular 
 misconceptions. Obviously, even if crops 
 grown by this method in desert regions 
 required less water, the difficulties in pro- 
 viding a somewhat smaller supply for 
 nutriculture would be essentially the same 
 as those encountered in providing a 
 larger amount for irrigation in soil. 
 There is no direct evidence that crops 
 produced by nutriculture require actually 
 less water than those grown in soil, if 
 the climatic conditions are the same. 
 
 Tomatoes grown side by side in soil 
 and in water culture in the same green- 
 house 12 afforded an opportunity to meas- 
 ure the relative amounts of water utilized. 
 The numbers of gallons of water used to 
 produce 100 pounds of fruit were as fol- 
 lows: soil, 222; water culture, 257. These 
 results indicate that somewhat more water 
 was used to produce a unit weight of fruit 
 under water culture than under soil con- 
 ditions. What seems to warrant emphasis, 
 however, is not the difference, but the 
 essential similarity in the amount utilized 
 by the plants grown in both media. This 
 is in agreement with the fact that the prin- 
 cipal use of water in producing a crop is 
 through evaporation by the plant— a re- 
 
 12 See footnote 11 on page 14. 
 
 [15] 
 
quirement common to both soil and nutri- 
 culture. The physiological characteristics 
 of each species of plant, the extent of leaf 
 surface, and the atmospheric conditions 
 are the determining factors in this re- 
 quirement. If a large crop is produced, 
 either in nutriculture or in soil, and if 
 climatic conditions favor high evapora- 
 tion of water from the plant, the amount 
 of water used in either case is necessarily 
 large. 
 
 Nutritional quality of the product is the 
 same. Modern research on vitamins and 
 on the role of mineral elements in animal 
 nutrition has justly aroused great public 
 interest. Here again much popular dis- 
 cussion relating to their effect in diets 
 and on health has been without scientific 
 basis. It is, therefore, not unexpected that 
 claims have been advanced for the superi- 
 ority of food produced by nutriculture. 
 
 As part of our investigation, careful 
 studies of chemical composition and gen- 
 eral quality have been made on tomatoes 
 of several varieties grown in a fertile soil, 
 and in sand- and water-culture media, 
 side by side in the same greenhouse, with 
 the same general cultural treatment. No 
 significant difference has been discovered 
 in the mineral content of the fruit de- 
 veloped on plants grown in the several 
 media. There is no scientific basis then 
 for referring to tomatoes grown in nutri- 
 culture as "mineralized." 
 
 Among the minerals most frequently 
 mentioned in this connection was calcium. 
 It may be added, as a point of general 
 interest, that all tomatoes, regardless of 
 the method by which they were grown, 
 contain but small amounts of calcium and 
 are not therefore an important source of 
 this mineral element in the diet. 
 
 Tomatoes harvested from the soil and 
 from water cultures could not be consist- 
 ently distinguished in a test of flavor and 
 general quality. 13 
 
 No significant difference could be 
 found in content of vitamins— carotene, 
 or provitamin A, and vitamin C, in the 
 fruit. 
 
 Caution: No claims of unusual nutri- 
 tional value for food products should be 
 accepted unless they are supported by re- 
 sults obtained in research institutes of 
 high standing. 
 
 The similarity in composition and gen- 
 eral quality of the tomatoes grown in soil 
 and water culture in the present experi- 
 ments, may be explained by the facts that 
 the climate and time of harvest were com- 
 parable and that the supply of mineral 
 nutrients was adequate in both cases. 
 Whether plants are grown in soil or nu- 
 triculture, climate and time of harvest 
 are, of course, the factors that most affect 
 quality and composition of plant product. 
 
 Nutrient deficiencies, insect attacks, and 
 diseases present similar problems. 
 
 When plants are grown in solutions 
 deficient in any of the nutrient ele- 
 ments, symptoms appear, usually in the 
 leaves. The series of photographs (plates 
 2 to 4) shows the general character of 
 foliage symptoms developed by the to- 
 mato plant for each essential element 
 omitted from experimental solutions. 
 
 Nutriculture does not protect plants 
 from any diseases except those strictly 
 soil-borne. In fact, certain other diseases 
 peculiar to water culture may sometimes 
 attack them. 
 
 The same insect pests attack plants 
 grown in all media. 
 
 Climatic requirements are the same. 
 Many inquiries have been received on the 
 possibility of growing plants in nutri- 
 culture in dimly lighted places, or at low 
 temperatures, under conditions which 
 would prevent growth of plants in soil. 
 Obviously, no nutrient solution can act 
 as a substitute for light and suitable tem- 
 perature. If there is doubt of the suita- 
 bility of a particular location or season 
 for the growth of any kind of plant, a 
 preliminary experiment should be made 
 
 13 The quality tests were conducted by Dr. 
 Margaret Lee Maxwell Kleiber of the Division 
 of Home Economics, and the carotene determi- 
 nations were made by Dr. Gordon Mackinney of 
 the Division of Food Technology, College of 
 Agriculture. 
 
 [16] 
 
Plate 1. A, B, Effect of forced aeration on asparagus plants grown in culture solutions: A, plants 
 grown in solution through which air was bubbled continuously; B, plants without forced aeration. 
 
 C, Asparagus plants grown in a nutrient solution in which boron, manganese/ zinc, and copper 
 were present in such small amounts as one part in several million parts of solution; D, plants grown 
 in solutions to which these elements were not added. 
 
 by growing the plant in good garden soil. 
 If the plant fails to make satisfactory 
 development in the soil medium because 
 of unfavorable light or temperature, fail- 
 ure may also be expected under water- 
 culture conditions. 
 
 Sunlight and suitable temperatures are 
 essential for green plants, in order that 
 they may carry on one of the fundamental 
 processes of plant growth, known as 
 photosynthesis. In this process, the ele- 
 ment carbon, which forms so large a 
 
 [17] 
 
Plate 2. Symptoms of mineral deficiencies shown by tomato plants: A, complete 
 nutrient solution; B, solution lacking nitrogen; C, solution lacking phosphorus; 
 D, solution lacking potassium. 
 
 part of all organic matter, is fixed by 
 plants from the carbon dioxide of the 
 atmosphere. This reaction requires a 
 large amount of energy, which is ob- 
 tained from sunlight. 
 
 Plants depend on photosynthesis for 
 their food, that is, for organic substances, 
 such as carbohydrates, fats, and proteins, 
 
 which provide them with energy and 
 enter into the composition of plant sub- 
 stance. The mineral nutrients absorbed 
 by roots are indispensable for plant 
 growth but do not supply energy and, in 
 that sense, cannot be regarded as "plant 
 food." 
 
 Animal life is also absolutely dependent 
 
 [18] 
 
i,!%- 
 
 
 G H 
 
 Plate 3. Symptoms of mineral deficiencies shown by tomato plants: E, solution 
 lacking calcium; F, solution lacking sulfur; G, solution lacking magnesium; 
 H, solution lacking boron. 
 
 on this ability of the green plant to fix 
 the energy of sunlight. 
 
 Favorable air temperatures are just as 
 necessary as in soil. An earlier report of 
 a preliminary experiment by other in- 
 vestigators suggested that under green- 
 house conditions, heating the nutrient 
 solution would produce large increases 
 in the yield of tomatoes." This is not con- 
 firmed by experiments we undertook in 
 a Berkeley greenhouse, which was un- 
 
 heated except on a few occasions to pre- 
 vent temperatures from falling below 
 50-55° Fahrenheit. Under the climatic 
 conditions studied, the beneficial effects 
 of heating the nutrient solution (to 70° F 
 in the fall- winter and to 75° F in the 
 spring-summer period) were not of sig- 
 nificance. If favorable air temperatures 
 
 14 Gericke, W. F., and J. R. Tavernetti. Heat- 
 ing of liquid culture media for tomato produc- 
 tion. Agricultural Engineering 17: 141-42, p. 
 184. 1936. 
 
 [19] 
 
Plate 4. Symptoms of mineral deficiencies shown by tomato plants: A, 
 right, iron deficiency; left, complete nutrient solution; B, left, manganese 
 deficiency; right, complete nutrient solution; C, left, copper deficiency; 
 middle, complete nutrient solution; right, zinc deficiency; D, left, molyb- 
 denum deficiency; right, complete nutrient solution. (Illustration from 
 recent unpublished results of D. I. Arnon and P. R. Stout.) 
 
 [20] 
 
are maintained, there seems to be no need 
 to heat the solution. 
 
 Attempts should not be made to guard 
 against frost injury or unfavorable 
 low air temperatures merely by heating 
 the nutrient solution. .Proper provision 
 should be made for direct heating of the 
 greenhouse. This may be found desirable 
 even when danger from low temperatures 
 is absent, in order to control humidity 
 and certain plant diseases. 
 
 These experiments on tomatoes sug- 
 gest that if greenhouse temperatures are 
 properly controlled, the solution tempera- 
 ture will take care of itself. Certainly no 
 expense should be incurred for equip- 
 ment for heating solutions, either in a 
 greenhouse or outdoors, until experimen- 
 tation has shown such heating to be 
 profitable. 
 
 There is no one best solution tempera- 
 ture. The physiological effects of the 
 temperature of the solution are inter- 
 related with those of air temperature and 
 of light conditions. 
 
 Most amateurs who try the nutriculture 
 method will grow plants in warm seasons 
 and probably will not wish to complicate 
 their installation by the addition of heat- 
 ing devices. Anyone who desires to test 
 the influence of heating the culture solu- 
 tion should make comparisons of plants 
 grown under exactly similar conditions, 
 except for the difference of temperature 
 in the solutions. 
 
 Composition of nutrient solutions 
 may vary 
 
 No one nutrient solution is superior to all 
 other solutions. Thousands of requests 
 have been received by the Station for 
 formulas for nutrient salt solutions. It is 
 often supposed that some remarkable 
 new combination of salts has been de- 
 vised and that the prime requisite for 
 growing crops in solutions is to use this 
 formula. The fact is, there is no one com- 
 position of a nutrient solution which is 
 always superior to every other composi- 
 tion. Plants have marked powers of adap- 
 
 tation to different nutrient conditions. If 
 this were not so, plants would not be 
 growing in varied soils in nature. We 
 have already emphasized that within cer- 
 tain ranges of composition and total con- 
 centration, fairly wide latitude exists in 
 the preparation of nutrient solutions suit- 
 able for plant growth. Many varied solu- 
 tions have been used successfully by 
 different investigators. Even when two 
 solutions differ significantly in their 
 effects on the growth of a particular kind 
 of plant under a given climatic condition, 
 the relation between the solutions will not 
 necessarily be the same with another kind 
 of plant, or with the same kind of plant 
 under another climatic condition. 
 
 Concentration of the solution changes 
 as the plants grow. Another point con- 
 cerning nutrient solutions needs to be 
 stressed. After plants begin to grow, the 
 composition of the nutrient solution 
 changes because the constituents are ab- 
 sorbed by plant roots. How rapidly the 
 change occurs depends on the rate of 
 growth of the plants and the volume of 
 solution available for each plant. Even 
 with large volumes of solutions, some 
 constituents may become depleted in a 
 comparatively short time by rapidly 
 growing plants. This absorption of nu- 
 trient salts causes not only a decrease in 
 the total amounts of salts available, but 
 a qualitative alteration as well, since not 
 all the nutrient elements are absorbed at 
 the same rates. One secondary result is 
 that the acid-base balance (pH) of the 
 solution may undergo changes which in 
 turn may lead to the precipitation of 
 certain essential chemical elements (par- 
 ticularly, iron and manganese) so that 
 they are no longer available to the plant. 
 Also to be considered are the effects of 
 salts added with the water (discussed 
 later). 
 
 Constant control of the solution is neces- 
 sary. For these various reasons, the main- 
 tenance of the most favorable nutrient 
 medium throughout the life of the plant 
 involves not merely the selection of an 
 
 [21] 
 
appropriate solution at the time of plant- 
 ing but also continued control, with either 
 the addition of chemicals when needed 
 or the replacement of the whole solution 
 from time to time. Proper control of cul- 
 ture solutions is best guided by observa- 
 tions of the crop and by chemical analyses 
 of samples of the solution taken periodi- 
 cally. 
 
 The objective of controlling the nutri- 
 ent solutions is not to maintain a fixed 
 composition of some "ideal" nutrient 
 solution, but rather to provide the plant 
 at each stage of its growth with a sufficient 
 quantity of each essential element, within 
 suitable ranges of total concentration and 
 fairly broad limits of ionic proportions. 
 
 Test tap water for salt content. For the 
 purpose of exact control in his experi- 
 ments, the plant physiologist prepares 
 his solutions with distilled water. The 
 commercial grower and the amateur are 
 usually limited to the use of domestic or 
 irrigation water, which contains various 
 salts, including such sodium salts as 
 sodium chloride, sodium sulfate, and 
 sodium bicarbonate, as well as calcium 
 and magnesium salts. 
 
 Most waters suitable for irrigation or 
 for drinking can be utilized in the water- 
 culture method, but the adjustment of the 
 reaction (pH) in the nutrient solution 
 depends on the composition of the water. 
 Some waters may be unfit for use in the 
 solution because of high sodium salt con- 
 tent. Even with a water only moderately 
 high in it, the salt may concentrate in the 
 nutrient solution with possible unfavor- 
 able effects on the plant. This is particu- 
 larly true when large amounts of water 
 have to be added to the tanks and the 
 solutions are not changed. In one in- 
 stance, a well water was highly toxic be- 
 cause it contained too high a concentration 
 of zinc, apparently derived largely from 
 circulation through galvanized pipes. 
 This same water, however, was not in- 
 jurious to tomato plants grown in soil 
 because of the absorbing power of the 
 soil for zinc. 
 
 Nutrients cannot take the place of sun- 
 shine. As already indicated, the successful 
 growth of a crop is dependent on sunlight 
 and temperature and humidity conditions, 
 as well as on the supply of mineral nutri- 
 ents furnished by the culture medium. 
 Complex interrelations exist between cli- 
 matic conditions and the utilization of 
 these nutrients. The relation of nitrogen, 
 nutrition, and climatic conditions to fruit- 
 fulness has often been stressed. In some 
 localities, deficient sunshine in winter 
 months may limit the growth of many 
 greenhouse crops, no matter what nutri- 
 ent conditions are present in the culture 
 solution. 
 
 The same initial composition may supply 
 nutrient requirements of many kinds of 
 plants. The question is frequently asked: 
 Does each kind of plant require a differ- 
 ent kind of nutrient solution? The answer 
 is that if proper measures are taken to 
 provide an adequate supply of nutrient 
 elements, then many kinds of plants can 
 be grown successfully in nutrient solu- 
 tions of the same initial composition. 
 (The same fertile soil can produce high 
 yields of many kinds of plants.) 
 
 The composition of the nutrient solu- 
 tion should always be considered in rela- 
 tion to the total supply as well as to the 
 proportions of the various nutrient ele- 
 ments. To give a specific illustration: as- 
 sume that several investigators prepare 
 nutrient solutions of the same formula, 
 but one uses 1 gallon of the solution for 
 growing a certain number of plants, an- 
 other 5 gallons of solution, and still an- 
 other 50 gallons. If plants were grown to 
 large size, each investigator would reach 
 a different conclusion as to the adequacy 
 of the nutrient solution employed, al- 
 though the initial composition was the 
 same in all cases. The investigator using 
 the small volume might find that his 
 plants became starved for certain nutri- 
 ents, while the one using the larger vol- 
 ume experienced no such difficulty. In 
 fact, the precise initial composition of a 
 culture solution has very little signifi- 
 
 [22] 
 
cance, since the composition undergoes 
 continuous change as the plant grows and 
 absorbs nutrients. 
 
 The rate and nature of this change de- 
 pends on many factors, including total 
 supply of nutrients. An adequate supply 
 of nutrients involves (1) volume of solu- 
 tion in relation to the number of plants 
 grown, stage of growth of the plant, and 
 rate of absorption of nutrients, and (2) 
 frequency of changes of solution. 
 
 Apart from the question of adequate 
 supply of nutrients, certain special re- 
 sponses of different species of plants have 
 to be taken into account in the manage- 
 ment of nutrient solutions. Plants vary 
 in their tolerance to acidity and alkalin- 
 ity. They also differ in their need for root 
 aeration and in susceptibility to injury 
 from excessive concentrations of ele- 
 ments like boron, manganese, copper, 
 
 and zinc. Some plants may be especially 
 prone to yellowing because of difficulty 
 in absorbing enough iron or manganese. 
 Some may succeed best in a nutrient solu- 
 tion more dilute than is employed for 
 most kinds of plants. Unfavorable re- 
 sponses by certain plants to high nitrogen 
 supply in relation to fruiting, under cer- 
 tain climatic conditions, may require con- 
 sideration. 
 
 Since the adaptation of a nutrient solu- 
 tion to the growth of any particular kind 
 of plant depends on the supply of nutri- 
 ents and on climatic conditions, there is 
 no possibility of prescribing a list of 
 nutrient solutions, each one best for a 
 given species of plant. 15 Some general 
 type of solution, such as one of those 
 described in this circular, should be tried 
 first. It may be modified later by experi- 
 ment if found necessary. 
 
 DIRiCTtONS FOR THE water-culture method 
 
 The preceding discussion dealt with 
 general considerations bearing on the use 
 of any soilless method of plant growth, 
 especially by those who contemplate com- 
 mercial ventures. What follows, deals with 
 specific directions on how to proceed. 
 These are given in response to numerous 
 inquiries received from amateurs, pros- 
 pective growers, teachers, and many 
 others. As stated earlier, this circular 
 describes only one technique for growing 
 plants without soil, namely, the water- 
 culture method. Other publications avail- 
 able elsewhere (see footnote 7, page 9) 
 give details of other techniques. 
 
 The type of container 
 
 The selection of a container depends 
 on the kind of plant to be grown, the 
 length of the growing period, and the 
 purpose for which the plants are grown. 
 
 In investigational work, 1- or 2-quart 
 Mason jars provided with cork stoppers 
 often serve as culture vessels (fig. 5). 
 
 Sometimes 5- or 10-gallon earthenware 
 jars are more suitable. Small tanks of 
 various dimensions have been extensively 
 used. For certain special investigations, 
 shallow trays or vessels of Pyrex glass 
 are required. Figure 6 shows the varied 
 types of containers used at the Station 
 for nutrient solutions in research prob- 
 lems. 
 
 For demonstrations in schools. Mason 
 jars covered with brown paper to exclude 
 light are excellent for demonstrations in 
 schools (fig. 5). The jars should have 
 cork stoppers in which one or more holes 
 have been bored (sometimes a slit is also 
 made in the cork ; see fig. 1 ) . Plants are 
 fixed in the holes with cotton. Wheat or 
 barley plants are very suitable for these 
 
 15 A number of inquiries have been received 
 regarding the culture of mushrooms. The water- 
 culture method under discussion is unsuited to 
 the culture of mushrooms. These plants require 
 organic matter for their nutrition and differ in 
 this way from green plants, which can grow 
 in purely mineral nutrient solutions like those 
 described in this circular. 
 
 [23] 
 
demonstrations, since they may be grown 
 in the jars without any special arrange- 
 ments for aeration. 
 
 For small-scale cultures. Two or 4- 
 gallon crocks may be serviceable for 
 small-scale cultures. Perforated corks 
 fitting into specially constructed covers, 
 or a porous bed of the kind described 
 later, support the plants. Other useful 
 containers are sheet metal tanks, such as 
 those shown in figure 6. The dimensions 
 of tanks are determined by the objective. 
 A tank of moderate size, adapted to many 
 purposes, is 30 inches long, 30 inches 
 wide, and 8 inches deep (fig. 2, p. 9 and 
 fig. 6, B) . A smaller one, 30 inches long, 
 12 inches wide, and 8 inches deep, is con- 
 venient for use in many experiments (fig. 
 6, C) . In general, the tanks should be 
 shallow, their length and width deter- 
 mined by convenience and economy. 
 They should have metal or wooden covers 
 perforated to hold corks (fig. 6, A, C, 
 D) which support the plants and in which 
 the plants are fixed with cotton (fig. 2). 
 
 For commercial water culture. For large- 
 scale experimental installations or for 
 commercial water culture, long, narrow, 
 shallow tanks have been employed. They 
 may be constructed of wood, cement, 
 sheet metal, or other sufficiently cheap 
 materials which do not give off toxic sub- 
 stances. Wooden tanks must be made 
 water tight. Redwood has been reported 
 to give off toxic substances and, therefore, 
 may require their removal by prelimi- 
 nary leaching. Concrete tanks should 
 also have thorough leaching before use. 
 Caution: All tanks should be painted on 
 the inside with asphalt or some other 
 paint harmless to plants. Most ordinary 
 paints cannot be used because of their 
 toxic substances. Galvanized iron, even 
 when coated with asphalt paint, may 
 cause trouble if any of the paint scales 
 off. Black iron tanks, well painted with 
 asphalt (fig. 6, A) have proved satis- 
 factory for experimental work. 
 
 In experimental installations requiring 
 large tanks, plants such as tomatoes were 
 
 Fig. 5. Corn and sunflower plants grown in 
 nutrient solution contained in 2-quart Mason 
 jars. Note method of placing plants in perfo- 
 rated corks. The jars are covered with thick 
 paper to exclude light. 
 
 supported in perforated cork, fitted into 
 specially constructed metal covers. In 
 commercial culture, however, a porous 
 bed is commonly used. 
 
 Nature of the bed 
 
 Any good carpenter or mechanic can 
 design and construct tanks and frames 
 suitable for commercial nutriculture. 
 Such installations generally consist of 
 large tanks with porous beds for support- 
 ing the plants. (In experimental work, 
 the perforated cork often serves this pur- 
 pose.) The beds in turn are supported by 
 heavy chicken wire netting (1-inch mesh) 
 coated with asphalt paint and stretched 
 tightly across a frame that fits the top of 
 
 [24] 
 
the container. This technique was first 
 suggested by W. F. Gericke. 30 
 
 Some suggestions for building the frame. 
 
 1. The wire-netting must be stretched 
 tightly across the frames and must be 
 immediately above the surface of the solu- 
 tion when the tank is full. 
 
 are: pine excelsior, peat moss, pine shav- 
 ings or sawdust, rice hulls. Certain mate- 
 rials are toxic to plants. For this reason, 
 redwood should usually be avoided. In 
 experiments carried on in Berkeley with 
 tomatoes, potatoes, and certain other 
 plants, a layer of pine excelsior 2 or 3 
 
 Fig. 6. Various types of containers for carrying on water-culture experiments: 
 
 A, Large iron (not galvanized) tank painted inside with asphalt paint, outside 
 with aluminum paint. Dimensions: 10 ft. x 2V2 ft. x 8 in. Shows one section of 
 metal cover. Perforated corks for supporting plants are fixed in the holes (fig. 2). 
 Wooden frames containing bedding material may also be set over these tanks, 
 as shown in figure 7. 
 
 B, Iron tank of dimensions: 30 in. x 30 in. x 8 in. 
 
 C, Iron tank of dimensions: 30 in. x 12 in. x 8 in. 
 
 D, Iron tank of dimensions: 15!/2 in. x IOV2 in. X 6 in. 
 
 E, Graniteware pan 16 in. x 1 1 in. x 2V2 in. used for growing small plants. Per- 
 forated metal covers, as shown in A, C, and D, may be used on all metal tanks 
 or trays. The number of holes in the cover can be varied according to the number 
 and size of plants to be grown. 
 
 F and G, Pyrex dish and beaker used for special experiments designed to study 
 the essentiality of certain chemical elements required by plants in minute quantity, 
 such as zinc, copper, manganese, and molybdenum. The covers for these con- 
 tainers, shown in the illustration, are molded from plaster of Paris and then 
 coated with paraffin. 
 
 2. Cross supports may be needed to 
 keep the wire from sagging (fig. 7) . 
 
 3. Several narrow sections of the frame 
 may be left uncovered by wire and fitted 
 with wooden covers instead. The latter 
 may be removed easily for inspection of 
 roots and for adding water or chemicals 
 to the solution. 
 
 Some porous materials that may be 
 used. The layer of the porous material is 
 generally 3 or 4 inches thick— thicker 
 when tubers or fleshy roots develop in the 
 bed. Some inexpensive bedding materials 
 
 inches thick, with a superimposed layer 
 of rice hulls about 1 or 2 inches thick, 
 has produced no toxic effects. For plants 
 that develop tubers or fleshy roots, some 
 finer material may possibly need to be 
 mixed with the excelsior. This is also 
 essential when small seeds are planted in 
 
 10 Gericke, W. F. Aquaculture : a means of 
 crop production. American Journal of Botany 
 16: 862. 1929. The general arrangement of this 
 type of bed was described by: Gericke, W. F., 
 and J. R. Tavernetti. Heating of liquid culture 
 media for tomato production. Agricultural Engi- 
 neering 17: 141^12, p. 184. 1936. 
 
 [25] 
 
the bed to prevent their falling into the 
 solution and to effect good contact of the 
 moist material with the seed. In all cases 
 the bed must be porous and permit free 
 access of air. 
 
 Care of the porous material. Seeds may 
 be planted in the moist beds, or young 
 plants from flats may be set in them with 
 
 for plants differ greatly in this require- 
 ment. In general, shallow, open tanks 
 with porous beds facilitate aeration of 
 the root system. It need not be assumed, 
 however, that these beds assure the best 
 growth for such plants as tomatoes, which 
 have a high oxygen requirement. In one 
 series of experiments, 17 tomato plants 
 
 Fig. 7. General arrangement of tank equipment and method of planting: A, a 
 frame supporting a wire screen fits over the metal tank (fig. 6, A) filled with the 
 nutrient solution; B, tomato plants are placed with their roots immersed in 
 the nutrient solution; a layer of excelsior is spread over the netting, as shown 
 in the far end of the tank; C, the planting is completed by spreading a layer of 
 rice hulls over the excelsior. 
 
 their roots in the nutrient solution. When 
 seeds are planted in the bed, they must 
 of course be kept moist until the roots 
 grow into the solution below. Occasional 
 sprinkling will provide enough moisture 
 for the development of tubers, bulbs, and 
 fleshy roots. Great care should be ob- 
 served to prevent waterlogging of the bed. 
 This results from immersion of the lower 
 portion of the bed in the solution and 
 leads to exclusion of air and to undesir- 
 able bacterial decompositions. 
 
 Aeration of the root system 
 
 In water culture, special attention has 
 to be given to aeration of the root system, 
 
 were grown in large shallow tanks pro- 
 vided with porous beds, but without any 
 special provision for aeration. A parallel 
 culture was aerated by bubbling air 
 through the solution. The latter showed a 
 significant improvement in growth and 
 yield, although the yields from the un- 
 aerated beds were at least as large as any 
 previously reported for this technique. 
 
 Roots may develop in beds as well as 
 in the solution, when porous beds are 
 used. It has been suggested that for such 
 plants as tomatoes, the additional roots in 
 the bed may be essential for supplying 
 certain factors required for the growth 
 
 17 See footnote 11 on page 14. 
 
 [26] 
 
of stem and for the prevention of chloro- 
 sis. According to this hypothesis, even 
 with adequate aeration, normal growth 
 would be impossible if the roots were con- 
 tinuously submerged in the nutrient solu- 
 tion. No support for this hypothesis was 
 found in an experiment with tomatoes in 
 Berkeley. The plants were grown in metal 
 tanks provided with metal covers, so con- 
 structed that the level of the nutrient solu- 
 tion was automatically maintained at the 
 top of the tanks. When adequate aeration 
 was provided, normal growth and devel- 
 opment resulted without a porous bed 
 and with the roots continuously sub- 
 merged. 
 
 Bubbling air through the solution. It is 
 sometimes difficult to supply adequate 
 oxygen when plants are grown in small 
 containers and a large root system is to 
 be developed. Bubbling air or circulating 
 the solution is helpful in such cases. Va- 
 rious devices, such as porous carbon 
 pipes and glass tubes, can be used for 
 this purpose. In general, too vigorous agi- 
 tation of the solution should be avoided 
 as it may harm tender roots. A continuous 
 stream of small bubbles of air gives good 
 results. Certain methods of circulating 
 culture solutions not only bring about 
 effective aeration but, in addition, equal- 
 ize the supply of nutrients. Circulation of 
 the nutrient solution from a central reser- 
 voir was used successfully in one com- 
 mercial greenhouse. For small scale or 
 experimental installations, special devices 
 for bubbling air or circulating the nutri- 
 ent solution have been described. 18 
 
 Planting procedures 
 
 How to plant. Seeds may be planted 
 directly in the moist bed. In that case, 
 the whole bed must be installed and 
 moistened before planting is begun. 
 
 Other seeds— cereals, for example- 
 may be germinated between layers of 
 moist filter paper or paper toweling. This 
 method is recommended if plants are to 
 be fixed in corks and grown in jars or 
 tanks with perforated metal or wooden 
 
 covers. As soon as germination begins, 
 the upper layer of moist paper is removed 
 and the seedlings allowed to grow on the 
 moist paper bed until they are large 
 enough to be placed in corks. An excess 
 of water is then added to the paper and 
 the seedlings carefully removed without 
 damage to the roots. 
 
 Sometimes it is preferable to grow 
 seeds in flats of good loam and then 
 choose the most vigorous seedlings for 
 transplanting into the bed. Just before 
 transplanting, the soil must be thoroughly 
 soaked with water so that the plants may 
 be removed with the least possible injury 
 to the roots. These should be rinsed free 
 of the soil with a light stream of water 
 and immediately set either in corks or in 
 beds with the roots immersed in the solu- 
 tion. In the latter case, the layer of excel- 
 sior is built up over the wire screen as 
 the roots are placed in the solution, and 
 the layer of rice hulls is added last 
 (%• 7). 
 
 How to space plants. No general advice 
 can be offered as to the best spacing. 
 This depends on the kind of plant and on 
 light conditions. Individual experience 
 must guide the grower. In our experi- 
 ments, tomato plants were set close to- 
 gether, in some instances 20 plants to 25 
 square feet of solution surface. 
 
 Managing the solutions 
 
 When to add water to tanks. In starting 
 the culture, the tank is filled with solution 
 almost to the level of the wire netting on 
 the bottom of the bed. As they grow, the 
 plants absorb water, or it evaporates from 
 the surface of the solution, thus reducing 
 its level in the tank. After the root system 
 is sufficiently developed, this level is 
 usually maintained from one to several 
 inches below the lower part of the bed 
 to facilitate aeration. Since the solution 
 
 18 Furnstal, A. F., and S. B. Johnson. Prepara- 
 tion of sintered Pyrex glass aerators for use in 
 water-culture experiments with plants. Plant 
 Physiology 11: 189-94. 1936. Compare also J. 
 W. Shive and W. R. Robbins in the citation 
 given in footnote 7, page 9. 
 
 [27 
 
level should not be permitted to fall very 
 far, however, water must be added at reg- 
 ular intervals. 
 
 As pointed out earlier, when large 
 amounts of water have to be added, ex- 
 cessive accumulations of certain salts 
 contained in the water may occur. This 
 is especially likely to happen if the salt 
 content of the water is high. To avoid this 
 difficulty, the entire solution is changed 
 whenever the salt concentration becomes 
 high enough to influence the plant ad- 
 versely. Should plants be injured, how- 
 ever, by the presence in the water of high 
 concentrations of elements like zinc, 
 changing solutions will not prevent in- 
 jury. Because of the wide variation in the 
 composition of water from different 
 sources, no specific directions to cover 
 all cases can be given. 
 
 When to change the nutrient solution. 
 As they begin to grow, the plants absorb 
 the nutrient salts, thus causing the acidity 
 of the solution to change. More salts and 
 acid may be added. To know how much, 
 requires chemical tests on the solution. 
 When these cannot be made, an arbitrary 
 procedure may be adopted of draining 
 out the old solution every week or two, 
 immediately refilling the tank with water 
 and adding nutrients as at the beginning 
 of the culture. The number of changes of 
 solution required will depend on the size 
 of plants, how fast they are growing, and 
 on the volume of the solution. 
 
 The nutrients should be distributed to 
 different parts of the tank. To effect 
 proper mixing, fill the tank at first only 
 partly full (but keep most of the roots 
 immersed), add the salts, and complete 
 the filling to the proper level with a rapid 
 stream of water, so directed as not to in- 
 jure the roots. 
 
 How to test and adjust acidity of water 
 and nutrient solution. Ordinarily some 
 latitude is permissible in the degree of 
 acidity (pH) of the nutrient solution. For 
 most plants, a moderately acid reaction 
 (from pH 5.0 to 6.5) is suitable. If dis- 
 tilled water is used in the preparation of 
 
 nutrient solution, no adjustment of its 
 reaction is necessary. If tap water is used, 
 a preliminary test of its reaction should 
 be made. Water found alkaline should be 
 acidified before adding the nutrient salts. 
 This should be done when the solution is 
 first made up and at each subsequent 
 change of solution. 
 
 The chemicals required for testing 
 acidity of water or nutrient solution are: 
 
 1. Bromthymol blue indicator. This can 
 be obtained, with directions for use, from 
 chemical supply houses, in the form of 
 solutions or impregnated strips of paper. 
 
 Strips of other test papers covering a 
 wide range of acidity are also now avail- 
 able on the market. The amateur who 
 understands their use will find them con- 
 venient for adjusting the acidity of water 
 as well as that of the nutrient solution. 
 
 2. Sulfuric acid. Purchase a supply of 
 3 per cent (by volume) acid of chemically 
 pure grade. (Concentrated, chemically 
 pure sulfuric acid may be purchased and 
 diluted to 3 per cent strength, but the con- 
 centrated acid is dangerous if handled 
 by inexperienced persons.) This 3 per 
 cent acid may be further diluted with 
 water, if a preliminary test indicates the 
 need of only small additions of acid. 
 
 Test the degree of acidity of a measured 
 sample of the water or nutrient solution 
 (a quart, for example) by noting the 
 color of the added indicator or test paper 
 immersed in the solution. When bromthy- 
 mol blue indicator is used, a yellow color 
 indicates an acid reaction (with no 
 further adjustment necessary) ; green, a 
 neutral reaction ; blue, an alkaline one. 
 
 If the original color is green or blue, 
 add the dilute sulfuric acid (3 per cent 
 or less in strength), slowly with stirring 
 until the color just changes to yellow 
 (indicating approximately pH 6). Do 
 not add more beyond this point, since the 
 yellow color will also persist when exces- 
 sive amounts of acid are added. Record 
 the amount of acid required. 
 
 Finally, add a proportionate amount 
 of the acid to the water or nutrient solu- 
 
 [28] 
 
tion in the culture tank or vessel, having 
 first determined how much it holds. 
 
 Modification of the solution. Since con- 
 siderable latitude is permissible in the 
 composition of nutrient solution, analysis 
 of tap water is not indispensable, unless 
 the content of mineral matter is very high. 
 Some waters may contain so much cal- 
 cium, magnesium or sulfate, however, 
 that further additions of these nutrient 
 elements are unnecessary, or even un- 
 desirable. As the objective should be to 
 approximate the intended composition of 
 the nutrient solution, taking into account 
 the salt already present in the water, 
 analysis of it is useful. 
 
 Prepared salt mixtures not recom- 
 mended. Many amateurs have become in- 
 terested in the purchase of mixtures of 
 nutrient salts ready for use. Various in- 
 dividuals and firms have offered such 
 mixtures for sale in small packages. 
 Clearly a prepared salt mixture does not 
 obviate the difficulties which may be met 
 in growing plants in water culture. Re- 
 cently, some firms have made highly mis- 
 leading claims for the salt mixtures they 
 sell. The Station makes no recommenda- 
 tion with regard to any salt mixture. The 
 fact that a mixture is registered with the 
 California State Department of Agricul- 
 ture, as required by the law governing 
 sale of fertilizers, implies no endorsement 
 for use of the product. The directions 
 given later will, we hope, help the amateur 
 to prepare his own nutrient solutions. 
 
 Chemically pure salts commonly em- 
 ployed in making nutrient solutions for 
 scientific experiments would be too ex- 
 pensive for commercial practice. A num- 
 ber of ordinary fertilizer salts can serve 
 in the production of crops by nutricul- 
 ture methods. Recent developments in 
 the fertilizer industry have made avail- 
 able cheap salts of considerable degree 
 of purity. Some commercial salts, how- 
 ever, contain impurities (fluorine, for 
 example, is commonly found in phosphate 
 fertilizers) which may be toxic to plants 
 under water-culture conditions. 
 
 Selecting the nutrient solution 
 
 As stated before, there is no one nutri- 
 ent solution which is always superior to 
 every other solution. Many solutions may 
 be used with good results. Those de- 
 scribed below have been found satisfac- 
 tory with various species of plants in 
 experiments conducted in Berkeley, with 
 a source of good water. 
 
 The composition of the solutions is 
 given in two forms: (A) by rough meas- 
 urements adapted to the amateur without 
 special weighing or measuring instru- 
 ments, and (B) in more exact terms for 
 those with some knowledge of chemistry 
 and the proper facilities for more ac- 
 curate experimentation. These facilities 
 would include chemical glassware, a 
 chemical balance, and a supply of C.P. 
 (chemically pure) chemicals. 
 
 Preparing the nutrient solution 
 
 Directions for amateurs. Either one of 
 the solutions given in table 2 may be 
 tried. Solution 2 may often be preferred 
 because the ammonium salt delays the 
 development of undesirable alkalinity. 
 The salts are added to the water, prefer- 
 ably in the order given. 
 
 To either of the solutions, add the ele- 
 ments iron, boron, manganese, and in 
 some cases, zinc, and copper, which are 
 required by plants in minute quantities. 
 There is danger of toxic effects if much 
 greater quantities of these elements are 
 added than those indicated later in the 
 text. Molybdenum and possibly other ele- 
 ments required by plants in minute 
 amounts will be furnished by impurities 
 in the nutrient salts or in the water, and 
 need not be added deliberately. 
 
 a) Boron and Manganese Solution. 
 Dissolve 3 teaspoons of powdered boric 
 acid and 1 teaspoon of chemically pure 
 manganese chloride (MnCl 2 • 4H 2 0) in 
 a gallon of water. (Manganese sulfate 
 could be substituted for the chloride.) 
 Dilute 1 part of this solution with 2 parts 
 of water, by volume. Use 1 pint of the 
 
 [29 
 
diluted solution for each 25 gallons of 
 nutrient solution. 
 
 The elements in group a are added 
 when the nutrient solution is first pre- 
 pared and at all subsequent changes of 
 solution. If plants develop symptoms 
 characteristic of lack of manganese or 
 boron (see plate 4, B, and plate 3, H) , 
 solution a, in the amount indicated in the 
 preceding paragraph, may be added be- 
 tween changes of the nutrient solution or 
 between addition of salts needed in large 
 quantities. 10 But care is needed, for injury 
 may easily be produced by adding too 
 much of these elements. 
 
 b) Zinc and Copper Solution. Ordi- 
 narily this solution may be omitted, be- 
 cause these elements will almost certainly 
 be supplied as impurities in water or 
 chemicals, or from the containers. When 
 needed, (plate 4, C) additions are made 
 as for solution a. To prepare solution b, 
 dissolve 4 teaspoons of chemically pure 
 zinc sulfate (ZnS0 4 • 7H 2 0) and 1 tea- 
 spoon of chemically pure copper sulfate 
 
 (CuS0 4 • 5H 2 0) in a gallon of water. 
 Dilute 1 part of this solution with 4 parts 
 of water. Use 1 teaspoon of the diluted 
 solution for each 25 gallons of nutrient 
 solution. 
 
 c) Additions of Iron to Nutrient Solu- 
 tion. Generally, iron solution will need to 
 be added at frequent and regular inter- 
 vals, perhaps as often as twice a week. If 
 the leaves of the plant tend to become 
 yellow (see plate 4, A) even more fre- 
 quent additions may be required. A yel- 
 lowing or mottling of leaves, however, 
 can also arise from many other causes. 
 
 The iron solution is prepared as fol- 
 lows: Dissolve 1 level teaspoon of iron 
 tartrate (iron citrate or iron sulfate can 
 be substituted, but the tartrate or citrate 
 is often more effective than the sulfate) 
 in 1 quart of water. Add % cup of this 
 solution to 25 gallons of nutrient solution 
 each time iron is needed. 
 
 10 The University is not prepared to diagnose 
 symptoms on samples of plant tissues sent in 
 for examination. 
 
 TABLE 2. — Composition of Nutrient Solutions* 
 
 (The amounts given are for 25 gallons of solution) 
 
 Salt 
 
 Grade 
 of salt 
 
 Approximate 
 amount, 
 in ounces 
 
 Approximate 
 
 amount, in 
 
 level tablespoons 
 
 Solution 1 f 
 
 
 
 Potassium phosphate (monobasic) 
 
 Potassium nitrate 
 
 Technical 
 Fertilizer 
 Fertilizer 
 Technical 
 
 y 2 
 
 2 
 3 
 
 V/2 
 
 l 
 
 4 (of powdered salt) 
 
 Calcium nitrate 
 
 7 
 
 Magnesium sulfate (Epsom salt) 
 
 4 
 
 Solution 2f 
 
 
 
 Ammonium phosphate (monobasic) 
 
 Potassium nitrate 
 
 Technical 
 Fertilizer 
 Fertilizer 
 Technical 
 
 V2 
 
 2V 2 
 2V 2 
 
 2 
 
 5 (of powdered salt) 
 
 Calcium nitrate 
 
 6 
 
 Magnesium sulfate (Epsom salt) 
 
 4 
 
 * The University does not sell or give away any salts for growing plants in water culture. Chemicals may be 
 purchased from local chemical supply houses, or possibly may be obtained through fertilizer dealers. Some of 
 the chemicals may be obtained from druggists. If purchased in fairly large lots, the present price of the in- 
 gredients contained in 1 pound of a complete mixture of nutrient salts is approximately 5 to 10 cents for either 
 solution described above. 
 
 f To either of these solutions, supplements of elements required in minute quantity must be added; see 
 directions in the text. 
 
 [30] 
 
Directions for schools or technical lab- 
 oratories. For experimental purposes, the 
 use of distilled water and chemically pure 
 salts is recommended. Molar stock solu- 
 tions (except when otherwise indicated) 
 are prepared for each salt, and the 
 amounts indicated below are used. 
 
 Solution 1 ... , 
 
 cc in a liter of 
 nutrient solution 
 M KH2PO4, potassium acid 
 
 phosphate 1 
 
 M KNO3, potassium nitrate 5 
 
 M Ca(NOs) 2, calcium nitrate .. . 5 
 M MgSCX, magnesium sulfate. . . 2 
 
 Solution 2 . ... . 
 
 cc in a liter of 
 nutrient solution 
 
 M NH4H2PO4, ammonium acid 
 
 phosphate 1 
 
 M KNOs, potassium nitrate 6 
 
 M Ca(N0 3 )2, calcium nitrate ... 4 
 
 M MgSCX, magnesium sulfate. . . 2 
 
 To either of these solutions, add solu- 
 tions a and b below. 
 
 a) Prepare a supplementary solution 
 which will supply boron, manganese, 
 zinc, copper, and molybdenum, as fol- 
 lows: 
 
 Grams dissolved 
 Compound in 1 liter of H 2 
 
 H3BO3, boric acid 2.86 
 
 MnCl 2 • 4H 2 0, manganese 
 
 chloride 1.81 
 
 ZnS0 4 • 7H2O, zinc sulfate 0.22 
 
 CuSCX • 5H 2 0, copper sulfate. . 0.08 
 H2M0O4 • H 2 0, molybdic acid 
 
 (assaying 85 per cent M0O3) 0.02 
 
 Add 1 cc of this solution for each liter 
 of nutrient solution, when solution is first 
 prepared or subsequently changed, or at 
 more frequent intervals if necessary. 
 
 This will give the following concen- 
 trations : 
 
 Parts per million of 
 Element nutrient solution 
 
 Boron 0.5 
 
 Manganese 0.5 
 
 Zinc 0.05 
 
 Copper 0.02 
 
 Molybdenum 0.01 
 
 b) Add iron in the form of 0.5 per cent 
 iron tartrate solution or other suitable 
 iron salt, at the rate of 1 cc for each liter, 
 about twice a week, or as indicated by 
 appearance of plants. 
 
 [31 
 
 The reaction of the solution is adjusted 
 to approximately pH 6 by adding 0.1 N 
 H 2 S0 4 (or some other suitable dilution) . 
 
 Molar Solutions. The concentrations 
 of stock solutions of nutrient salts used 
 in preparation of nutrient solutions are 
 conveniently expressed in terms of mo- 
 larity. A molar solution is one containing 
 1 gram-molecule (mol) of dissolved sub- 
 stance in 1 liter of solution. (In all 
 nutrient-solution work, the solvent is 
 water.) A gram-molecule or mol of a 
 compound is the number of grams cor- 
 responding to the molecular weight. 
 
 Example 1, how to make a molar 
 solution of magnesium sulfate: The mo- 
 lecular weight of magnesium sulfate, 
 MgS0 4 -7H 2 is 246.50. One mol of 
 magnesium sulfate consists of 246.50 
 grams. Hence, to make a molar solution 
 of magnesium sulfate, dissolve 246.50 
 grams of MgS0 4 ■ 7H 2 in water and 
 make to 1 liter volume. 
 
 Example 2, how to make a one-twentieth 
 molar (0.05 M) solution of monocalcium 
 phosphate, Ca(H 2 P0 4 ) 2 ■ H 2 (used in 
 deficiency studies, below) : The molec- 
 ular weight of monocalcium phosphate, 
 Ca(H 2 P0 4 ) 2 • H 2 is 252.17. Hence 0.05 
 
 252.17 grams 
 
 molofCa(H 2 P0 4 ) 2 -H 2 Ois- 
 
 20 
 
 = 12.61 grams. Therefore, to make a 0.05 
 M solution of monocalcium phosphate, 
 dissolve 12.61 grams of Ca(H 2 P0 4 ) 2 # 
 H 2 in water and make to 1 liter volume. 
 
 Nutrient solutions for use in dem- 
 onstrating mineral deficiencies 
 in plants 
 
 In any experiment to demonstrate min- 
 eral deficiencies in plants, solution 1 or 
 solution 2 should be used as a control to 
 show normal growth in a complete solu- 
 tion. Below are given six solutions, each 
 lacking in one of the essential elements. 
 Similar solutions were used in producing 
 the deficiency symptoms shown in plates 
 2 and 3, with plants which had previously 
 been grown for several weeks in complete 
 nutrient solutions. 
 
Distilled water should be used in mak- 
 ing these solutions. 
 
 cc in a liter of 
 nutrient solution 
 
 a, Solution lacking nitrogen 
 
 0.5 M K 2 S0 4 5 
 
 M MgS0 4 2 
 
 0.05MCa(H 2 PO 4 ) 2 10 
 
 0.01MCaSO 4 200 
 
 b, Solution lacking potassium 
 
 MCa(N03) 2 5 
 
 M MgS0 4 2 
 
 0.05MCa(H 2 PO 4 ) 2 10 
 
 c, Solution lacking phosphorus 
 
 MCa(N0 3 ) 2 4 
 
 M KN0 3 6 
 
 M MgS0 4 2 
 
 d, Solution lacking calcium 
 
 M KNO3 5 
 
 M MgS0 4 2 
 
 M KH 2 P0 4 1 
 
 e, Solution lacking magnesium 
 
 MCa(N0 3 ) 2 4 
 
 M KNO3 6 
 
 M KH 2 P0 4 1 
 
 0.5 M K 2 S0 4 3 
 
 /, Solution lacking sulfur 
 
 MCa(N0 3 ) 2 4 
 
 M KNO3 6 
 
 M KH 2 P0 4 1 
 
 MMg(N0 3 ) 2 2 
 
 To any of these solutions, add iron and 
 the supplementary solution supplying 
 fjoron, manganese, zinc, copper, and 
 molybdenum as previously described (p. 
 29-31). For use with solution /, lacking 
 sulfur, a special supplementary solution 
 should be prepared in which chlorides 
 replace the sulfates. Also, sulfuric acid 
 should not be used in adjusting the re- 
 action of the nutrient solution. 
 
 In order to produce iron-deficiency 
 symptoms, plants should be grown in 
 glass containers; no iron should be added 
 to the otherwise complete nutrient solu- 
 tion. Similarly, it may be possible to 
 produce boron- or manganese-deficiency 
 symptoms with certain plants (tomatoes, 
 for example) by omitting either one of 
 these elements from the supplementary 
 solution. Zinc-, copper-, and molybdenum- 
 deficiency symptoms can usually be pro- 
 duced only by the use of a special 
 technique, the description of which was 
 published in a technical paper. 20 
 
 20 Stout, P. R., and D. I. Arnon. Experimental 
 methods for the study of the role of copper, 
 manganese, and zinc in the nutrition of higher 
 plants. American Journal of Botany 26: 144-49. 
 
 25m-l,'50(B7321) 
 
 [32]