UNIVERSITY OF CALIFORNIA AGRICULTURAL EXPERIMENT STATION 
 
 ~~. . ~~- .«..- . «*_._.. .. ..... BENJ. IDE WHEELER, PRESIDENT 
 
 COLLEGE OF AGRICULTURE 
 
 THOMAS FORSYTH HUNT, Dean and Director 
 
 BERKELEY h. e. van norman, vice-director and dean 
 
 University Farm School 
 
 CIRCULAR No. 200 
 May, 1918 
 
 GROWING THE FALL OR SECOND CROP 
 OF POTATOES IN CALIFORNIA 
 
 By STANLEY S. EOGERS 
 
 It is possible and profitable, over a large portion of California, to 
 grow a second or fall crop of potatoes, and this practice should be 
 encouraged where conditions are favorable, for practical experience 
 has shown that a heavier yield of better quality is realized than in 
 the case of early spring potatoes. 
 
 It is difficult to store potatoes successfully during the warmer 
 months, but those maturing in the fall may be kept in a satisfactory 
 condition until the following spring, which is often an advantage to 
 the grower. As a rule, higher prices prevail during the winter and 
 spring than are offered in the summer; this coupled with the larger 
 yields obtained, appears to be very encouraging for the future pro- 
 duction of fall potatoes. 
 
 It is imperative, however, that the soil be adapted to the needs 
 of this crop, and that sufficient irrigation facilities be available so 
 that the water may be applied when needed. The absence of heavy 
 frosts up to the middle of November is also an important condition. 
 
 Hoiv to Obtain Seed. — The seed may be obtained from the potatoes 
 stored over winter, or from the spring crop of the same year. Under 
 ordinary conditions the latter source of seed is preferable. 
 
 Growing Seed for Second Crop. — When home-grown seed is used, 
 the crop should be planted as soon in the spring as possible, the exact 
 time depending largely upon the climatic conditions. Under central 
 California conditions the seeding may be done during February and 
 March, but in the warmer sections it is possible to advance the time 
 of planting considerably. In the vicinity of Sacramento, the planting 
 is done from February 1 to March 15. 
 
 If an early maturing variety, such as the American Wonder, is 
 used, the crop may be dug during the latter part of June to the first 
 week in July. When using this crop for seed, experience has shown 
 that it should be harvested before full maturity. The most desirable 
 time to harvest is when the vines are changing from a yellow to a 
 brownish color. 
 
Harvesting and Curing the Seed. — If the crop is harvested at the 
 period shown above, the potatoes will not be fully matured and the 
 skin will slip very easily. After digging they should be exposed to 
 the sun from one-half to one hour before being picked up. If the day 
 is very hot, care should be taken not to allow them to be on the ground 
 too long, as they will sunburn very easily and become unfit for food, 
 storage, or seed. 
 
 After the crop has been exposed to the sun the desirable length of 
 time, the seed should be placed immediately in piles from two to four 
 feet high and covered with straw to a depth of from six inches to one 
 foot. These heaps, or stacks, should be sprinkled each day or so, 
 putting on enough water to soak into them thoroughly, but being 
 careful that no excess moisture is allowed to accumulate, for fear of 
 rotting the potatoes. The water may be applied through the straw. 
 
 If there is no danger of tuber-moth infestation, these piles may 
 be made under a tree or shade where they will be protected from 
 the heat, or at least partially shaded. Where this pest is troublesome, 
 it is best to store the potatoes in a building where the moth can not 
 gain entrance, or cover the piles each night with canvas. 
 
 The length of time the potatoes should remain in these piles is 
 somewhat dependent upon the condition of the tubers, climate and 
 season, but generally from one to two weeks is sufficient. After being 
 removed they should be dipped, cut and planted as soon as possible, 
 for the longer they are exposed, the weaker will be their germination 
 power. 
 
 The selection of seed potatoes should be made at the time of har- 
 vesting, and it is best to dig a certain portion of the crop by hand, 
 keeping the individual hills separated, and to select from these the 
 potatoes best suited for future propagation. If this method is pur- 
 sued, the condition of the hill, as a whole, should be noted and not 
 the individual potato. If the grower does not wish to use the hill 
 selection, he should at least save only those potatoes which conform 
 closely to the ideal of the type and variety; a medium sized potato, 
 free from disease, will be found more advantageous than the very 
 small or large tubers. 
 
 The proper selection of the seed is of extreme importance; where 
 this is carried on carefully and thoroughly, it will pay the grower to 
 select his own seed from one season to another. At the University 
 Farm vegetable garden, home-grown, selected potatoes have been used 
 for four years and the quality of the eight crops produced has im- 
 proved regularly. Should home-grown seed be used continually, 
 without proper regard to selection, it is probable that the quality 
 would soon deteriorate to a degree where new seed would have to be 
 imported. 
 
 Preparation of the Soil. — It is sometimes difficult to obtain a satis- 
 factory stand of potatoes when planting during very hot weather. 
 This is due to poor curing of the seed and especially to an unfavorable 
 condition of the soil. In preparing the field for planting the great 
 problem is to cool the soil sufficiently so that the seed will not be 
 burned. Following is the method commonly used by many of the 
 
market gardeners and at the University Farm, and appears to be 
 entirely satisfactory for the interior valleys and warmer sections of 
 the state. 
 
 From one week to ten days before planting, the exact time depend- 
 ing largely upon the character of the soil, the field should be irrigated 
 very heavily, so that the soil is thoroughly saturated. A second irri- 
 gation is given from two to four days before planting and as the 
 chief advantage of this irrigation is to cool the soil, a small amouut 
 of water is used. Where possible, the land should be flooded rather 
 than applying the water in furrows. It is not customary to work the 
 land between irrigations. 
 
 Planting. — Just previous to planting, the potatoes should be im- 
 mersed from one and one-half to two hours in a corrosive-sublimate 
 solution of a strength of one ounce of the material to eight gallons of 
 water. Extreme care should be exercised in handling this dip, as it 
 is very poisonous. A wooden receptacle, such as a barrel, should be 
 used for this purpose. 
 
 As soon as the soil is in proper condition, the field is plowed to a 
 depth of eight to twelve inches and the potatoes immediately planted. 
 In planting large areas, better success will be attained if the field is 
 worked in small tracts, planting as soon as possible after plowing. 
 The seed should be put in the ground at least five inches deep, prefer- 
 ably six or seven inches, in order to protect it as much as possible 
 from the heat and to prevent drying. Heavier seeding should be 
 practiced in planting at this season than is customary when seeding 
 under more congenial growing conditions. At least eight sacks of 
 medium sized potatoes per acre should be used. 
 
 The time of planting is governed by the locality and time at which 
 the first crop is in condition to be dug. For the central interior 
 valleys the planting season extends from July 7 to August 1. In the 
 southern part of the state the planting may be done from July 1 to 
 August 10. Many potatoes are planted after the dates given above, 
 but this is done at a considerable risk, owing to the liability of early 
 frosts which may kill the plants before they are mature, resulting in 
 a partial or total loss of the crop. 
 
 In many of the hot interior valleys, the potatoes maturing in 
 June and July are often internally discolored. This condition is 
 known as the Internal Brown Streak, and is not transmitted through 
 the seed, so that the affected tubers may be used for this purpose. 
 The grower, however, should not confuse this condition with several 
 of the parasitic diseases which discolor the potato, making it absolutely 
 unfit for seed. Should any doubt exist, a sample may be submitted 
 to the University of California, College of Agriculture. 
 
 Future Care of Crop. — The future care differs only slightly from 
 the methods used for growing the spring crop. After planting, the 
 field should be harrowed at least once a week until the plants appear, 
 for every effort must be made to keep as much moisture as possible in 
 the soil, since it is unwise to irrigate before a month to six weeks 
 after planting and the loss of moisture during the heat of the summer 
 is very rapid. As soon as the plants are four to eight inches high, 
 
the field should be irrigated and a second irrigation is given about 
 the time the plants are in full bloom. It is often desirable to apply 
 the water a third time, viz., before the vines start to mature. 
 
 Harvesting. — When an early or medium-early variety is used, the 
 crop may be harvested in November. Should it be desirable to store 
 the potatoes, they should not be dug until the vines have been killed 
 by frost, for in order that the crop may be held successfully, it should 
 be thoroughly matured. Should rain come before the crop is har- 
 vested, the tubers will not be injured, provided the soil drainage is 
 such that the water will not stand on the field. During periods in 
 which frosts are likely to appear, the potatoes should not be left 
 exposed over night. It is best to leave them on the ground from two 
 to four hours before sacking, in order that they may dry; this will 
 also help to mature them properly. 
 
 Storing. — There are several methods for storing during the winter. 
 Some leave the crop in piles in the field, protected from frost by straw 
 or sacks. This method is only used where the soil is of a sandy nature 
 so that no excess water will accumulate. The most common practice 
 for keeping potatoes in California over winter is to put them in sacks 
 and store in a weather-proof building. This should be well ventilated, 
 rain-proof, and as dark as possible. During warm days the house 
 should be closed and opened during the nights, provided the tempera- 
 ture is not too severe. 
 
 The third method is storing the potatoes in crates, placed in a 
 suitable building. Even under good storage conditions, losses are 
 sometimes sustained ; in order to store potatoes in a satisfactory man- 
 ner, they must be fully matured when dug and kept out of the light 
 as much as possible. 
 
 Varieties. — The American Wonder and White Rose varieties are 
 most commonly used when two crops are grown in one season. The 
 former is produced throughout the Sacramento and San Joaquin 
 valleys, and southern California. The latter is used chiefly in the 
 southern part of the state. 
 
 SUMMARY 
 
 The production of a second or fall crop of potatoes in many sec- 
 tions of California should be encouraged. 
 
 Potatoes ripening in the fall will keep much longer than, those 
 maturing during the spring or summer. 
 
 It is preferable to use the potatoes maturing in the spring for seed 
 from which to grow the fall crop. 
 
 A second crop of potatoes should be grown only where the soil 
 is adapted to its needs and where adequate irrigation is available. 
 
 It is often difficult to procure a satisfactory stand of plants when 
 planting during the extreme heat. This may be largely overcome by 
 curing the seed properly, and irrigating twice just previous to 
 planting. 
 
 In central California, the seed should be planted between July 7 
 and August 1 ; in southern California from July 1 to August 10. 
 
 Under ordinary conditions the crop will be ready to harvest during 
 November, but should not be dug until the plants have fully matured.