xO **C4, 
 
 
 Division of Agric 
 UNIVERSITY OF 
 
 PROPAGATION 
 
 of AVOCADOS 
 
 R. G. Piatt 
 Edward F. Frolich 
 
 CALIFORNIA AGRICULTURAL 
 
 ^ Experiment Station 
 
 Extension Service 
 

 THE PROPAGATION 
 
 of avocado trees for commercial production requires 
 attention to detail and extreme care at each step. The 
 avocado is a tree sensitive to weather and soil condition 
 and susceptible to certain pests, but the careful grower 
 can successfully propagate tree- with minimum trouble 
 by following the directions in this publication. This cir- 
 cular replaces the former Circular 463. 
 
 THE SEED AND SEEDLING 
 
 Selecting the seed . . . planting the seed . . . cart 1 of the 
 seedbed . . . the nursery . . . digging the seedling . . . care 
 of the nursery 
 
 page 3 
 
 BUDDED TREES 
 
 Budding the seedling . . . selecting the bu< 
 methods . . . digging the trees 
 
 budding 
 
 page 7 
 
 TIP GRAFTS 
 
 Container-grown seedlings . . . grafting the seedlings 
 
 page 10 
 
 TOPWORKING 
 
 Reasons for topworking . . . best time for topworking . . . 
 the bark graft . . . the notch graft . . . selecting the scion 
 
 tools for topworking . . . care of the grafted tree 
 
 page 13 
 
 THE AUTHORS 
 
 R. G. Piatt is Extension Subtropical Horticulturist. Riv- 
 erside. Edward F. Frolich is Technician IV, Department 
 of Plant Biochemistry, Agricultural Sciences. Los An- 
 geles. 
 
 JANUARY, 1965 
 
 In order that the information in our publications may be more intelligible it is sometimes necessary 
 to use trade names of products or equipment rather than complicated descriptive or chemical 
 identifications. In so doing it is unavoidable in some cases that similar products which are on the 
 market under other trade names may not be cited. No endorsement of named products is intended 
 nor is criticism implied of similar products which are not mentioned. 
 
AVOCADO PROPAGATION 
 
 A. 
 
 vocados may be propagated in a num- 
 ber of different ways. Nursery trees are 
 produced by budding or grafting selected 
 varieties on seedling rootstocks. Trees can 
 be grown from cuttings but the perform- 
 ance of such trees has not shown any 
 advantage over budded trees and most 
 varieties are difficult to root and estab- 
 lish. Older trees may be topworked to new 
 varieties by various types of grafts or by 
 budding into vigorous new shoots. This 
 circular describes the more common pro- 
 cedures for avocado tree production in 
 California, and methods that are used 
 under special conditions. 
 
 Avocado trees grown from seed usually 
 come into bearing slowly. The tree varies 
 extremely in yield and fruit type; the 
 fruit is rarely of acceptable quality. Even 
 if the fruit were good it would be difficult 
 to market because each tree would bear 
 fruit differing in size, color, shape, and 
 quality. In cold locations where it is diffi- 
 cult to establish nursery trees, growers 
 sometimes plant hardy seedlings directly 
 in the orchard. After the seedlings have 
 grown two or more seasons they can be 
 grafted to the desired variety. Seedling 
 trees are occasionallv used as windbreaks. 
 
 Avoid root rot infection 
 
 In the production of avocado nursery 
 trees every precaution should be taken to 
 insure freedom from infection with cin- 
 namon fungus (Phytophthora einna- 
 momi) . Infection of trees in the nursery 
 by this fungus has been a major cause of 
 spread of avocado root rot disease. 
 
 Under a voluntary program of the Cali- 
 fornia State Department of Agriculture, 
 avocado nursery stock may be certified if 
 grown under certain conditions. The gen- 
 eral provisions include hot water treat- 
 ment of the seed, growing the trees in 
 containers on raised benches or well- 
 drained, unbroken paved areas, fumigat- 
 ing or steam-sterilizing the soil, and 
 sanitation and isolation of the nursery. 
 
 Details of the regulations and methods 
 governing certification are available from 
 your local University of California Farm 
 Advisor or County Agricultural Commis- 
 sioner. Instructions for the hot water seed 
 treatment and soil fumigation are con- 
 tained in University of California Exten- 
 sion Circular 511, "Avocado Root Rot." 
 
 Whether or not trees are grown for 
 certification, by following the general 
 procedures of the program the grower 
 will minimize the risk of infection in his 
 nursery trees. 
 
 THE SEED AND SEEDLING 
 
 Rootstocks 
 
 In California, seedlings of the hardy Mex- 
 ican varieties are preferred for rootstocks. 
 Seedlings of the Guatemalan varieties are 
 not recommended because although they 
 make strong growth and produce vigor- 
 
 ous trees when budded or grafted, the 
 stocks are more susceptible to disease and 
 injury from cold. Mexican seedlings are 
 more resistant to lime-induced chlorosis, 
 dothiorella canker and verticillium wilt 
 than are Guatemalan seedlings. 
 
 [3 
 
Selecting the seed 
 
 Select seed from trees of a hardy Mexican 
 variety known to produce seedlings that 
 make vigorous, disease-free trees. It is 
 best to discard seed that is small for the 
 variety. If possible, the tree or trees 
 should be isolated so that they will not 
 receive pollen from less desirable varie- 
 ties. Topa Topa and Mexicola are the 
 varieties most commonly used as sources 
 of seed. Ganter and a number of other 
 Mexican varieties are also used. Certain 
 selections of the Duke variety have shown 
 moderate tolerance to phytophthora root 
 rot fungus, but they are not immune to 
 the disease. Nurserymen have not used 
 Duke seed extensively, due to its rela- 
 tively slow germination and variation in 
 seedling uniformity. 
 
 Seed sometimes carries the virus dis- 
 ease, sun blotch. Since some trees carry 
 the virus without visible symptoms, it is 
 important to know that seedlings from 
 trees used as a seed source produce dis- 
 ease-free trees when budded or grafted. 
 Seed can also carry the avocado root rot 
 disease. Fruit that has lain on infected 
 soil may be invaded by the fungus, and 
 many of the seeds will then infect the 
 nursery. Therefore it is wise to take seed 
 from sound, mature fruit, avoiding the 
 windfalls. Your Farm Advisor can assist 
 you in locating reliable seed. 
 
 Plant the seed soon after it is removed 
 from the fruit. Protect it from drying. 
 Since fruit of the Mexican varieties ma- 
 tures in the fall it will, in some cases, be 
 necessary to store the seed until spring if 
 the nursery is to be located out-of-doors. 
 If seed is packed in dry moss, sand, or 
 >;iv\<lust and stored in a cool location 
 (40° to 45° F), it may be kept for sev- 
 eral months. 
 
 Planting the seed for 
 
 standard nursery trees 
 
 Avocado seedlings should be grown in a 
 soil that has riexer been planted to avo- 
 cados or other crops which carry the root- 
 
 rotting cinnamon fungus or verticillium 
 wilt fungus. To insure freedom from dis- 
 ease it is best to treat the soil with a 
 recognized soil fumigant. Methyl bromide 
 and Vapam are currently recommended. 
 Sandy soil that has not recently been 
 manured is best; some growers prefer a 
 mixture of half sand and half loam. 
 
 A convenient and economical way to 
 grow seedlings for field planting is in 
 beds 12 inches deep, 3 to 4 feet wide, and 
 long enough to accommodate the number 
 of seeds desired. It is often desirable to 
 build a frame of 1- x 12-inch boards on 
 the soil surface and fill it with soil spe- 
 cially prepared or selected for the seed- 
 bed. If rodents are likely to be a problem, 
 place a wire netting under the frame be- 
 fore filling. It is sometimes necessary to 
 screen the top of the beds until the seed- 
 lings are well established, to prevent their 
 removal or damage by rats and squirrels. 
 
 Seed can also be planted directly in the 
 field in nursery rows. This requires spe- 
 cial care and does not permit culling 
 weak and offtype seedlings without leav- 
 ing blank spaces. In addition, some seeds 
 sprout more slowly than the rest, causing 
 an irregular stand. Some growers place a 
 paper cup or a hot cap over each seed to 
 protect it from drying and to facilitate 
 weed control. Covering seed in this way 
 allows the grower to use contact weed- 
 killing sprays in the nursery. 
 
 Plant seed with the large, flat end 
 down, leaving the tip flush with the soil 
 surface. Germination can be hastened by 
 cutting a thin slice off the tip and base of 
 the seed. This is not necessary when the 
 seed is planted immediately after it is re- 
 moved from the fruit. Be sure that the 
 soil makes firm contact with the seed. 
 Spread a layer of clean sand, sawdust, or 
 ground peat moss over the beds, deep 
 enough to cover the seeds Y± to % inch. 
 This prevents formation of a crust over 
 the soil after irrigation and will protect 
 the seeds from drying. Provide shade to 
 prevent sunburn of tender sprouts as they 
 emerge during hot weather. 
 
 [4] 
 
Seed spacing in the seedbed depends 
 upon the method of transplanting from 
 the seedbed to the nursery row. If seed- 
 lings are to be transplanted bare root, 
 that is without soil adhering to the roots, 
 seed can be planted at 2-inch intervals. If 
 seedlings are to be transplanted with soil 
 around their roots, plant them at 4-inch 
 intervals to permit easy digging. Seed 
 planted directly in the nursery row 
 should be spaced 14 to 16 inches apart. 
 
 Some growers prefer to plant in 2- x 
 2- x 8-inch paper pots to facilitate mov- 
 ing the seedlings into the nursery. If the 
 grower has a hothouse or hot bed, he can 
 plant seed as it becomes available. Seed- 
 lings grown in this way from fall or early 
 winter plantings will be ready to line out 
 in the nursery by spring. 
 
 In warmer locations seed planted in 
 the fall out-of-doors, or in a lath or cloth 
 shelter will also be ready to transplant by 
 spring. Seedlings lined out in spring 
 should be ready to bud by summer. 
 Under favorable conditions seedlings 
 from fall plantings made directly in nurs- 
 ery rows can also be budded during sum- 
 mer. In cooler locations field plantings 
 are made in March or April and budding 
 can begin in the fall. 
 
 Care of the seedbed 
 
 Keep the seed bed moist at all times. This 
 will require sprinkling every two or three 
 days. In cool locations germination is 
 hastened if the beds are covered with 
 plastic or black paper, which warms the 
 soil, decreases moisture loss, and discour- 
 ages weed growth. The paper must be 
 removed at the first sign of germination 
 to avoid injury to the tender shoots. 
 
 Germination requires about 30 days 
 when seed is planted in a hothouse or 
 out-of-doors in spring. Most of the seed- 
 lings will be ready to transplant 60 to 90 
 days after the seed is planted. Seed 
 planted out-of-doors in fall or winter usu- 
 ally requires 60 or more days to germi- 
 nate and the seedlings will be ready to 
 transplant 30 to 60 days after germina- 
 
 tion. Seedlings are ready to transplant 
 when they are 5 or 6 inches high. 
 
 It is neither necessary nor desirable to 
 fertilize avocado seedlings at this stage. 
 The seeds provide adequate nutrients. 
 
 The nursery 
 
 The nursery site should be as free as pos- 
 sible from frost, strong wind and ocean 
 breezes. The soil should be free from 
 rocks and well drained but should con- 
 tain enough clay to form a good ball 
 when the trees are dug. As with the seed- 
 bed, the soil should not have been planted 
 to avocados or other crops that may have 
 carried the cinnamon or verticillium fun- 
 gus. Avoid locations below established 
 avocado orchards or land formerly 
 planted to avocados, where drainage 
 water may carry disease to the nursery. 
 It will save expense and trouble if the 
 site is also free of noxious weeds such as 
 nutgrass, bermudagrass or morning glory. 
 It is important to have an ample supply 
 of good water available at all times. 
 
 Before planting, the soil should be 
 moist and worked to form a good plant- 
 ing bed. If furrows are used for irriga- 
 tion they should be established and tested 
 for grades before planting. Furrows 
 should rarerly be more than 100 feet 
 long. Adjust planting distances for equip- 
 ment. The usual practice is to space the 
 rows 3 feet apart and plant the seedlings 
 14 to 16 inches apart in the rows. 
 
 Digging the seedlings 
 
 When the seedlings are ready to trans- 
 plant, moisten the soil in the seedbed. 
 Begin at one end of the bed, draw the 
 soil away from the seedlings and remove 
 them with as many small roots as possi- 
 ble. Use special care to leave the seed 
 attached to the seedlings; otherwise they 
 will not make satisfactory growth. Plant 
 the seedlings immediately and protect 
 them from drying at all times. They can 
 be kept in moist burlap, moss or shavings 
 for a short time. Discard all weak and 
 ofTtype seedlings. They rarely produce 
 
 [5] 
 
good trees. Sort the good seedlings into 
 two or three sizes and plant the different 
 sizes in separate rows. This will give 
 a more uniform and better-appearing 
 nurser) . 
 
 Seedlings with four and five leaves can 
 be planted w ithout reducing the leaf sur- 
 face. Larger seedlings will do better if 
 half of each leaf is clipped off before 
 planting. Do not clip or damage the grow- 
 ing tip of the seedling. 
 
 It is I »est lo dig seedlings to be trans- 
 planted from the seedbed into large pots 
 or other containers with a ball of soil 
 around their roots. Seedlings grown in 
 small paper pots must have the pot re- 
 moved when transplanted to the nursery 
 
 
 
 —fo**k* 
 
 PtPE 
 
 A dibble 
 is easy 
 to make 
 
 
 
 
 V. 
 
 —3/8 OR S// 6 " 
 
 3" 
 
 Holes for planting are usually made 
 with a large dibble, and should be deep 
 enough to accommodate the whole root 
 system without bending. If the holes are 
 made deeper than necessary, the root can 
 be inserted to the full depth of the hole 
 and then lifted to the proper planting 
 level to straighten the tender root tips and 
 prevent formation of crooked taproots. 
 Plant the seedlings at the same level as in 
 the seedbed and press the soil firmly 
 around the roots and seed. 
 
 As soon as the seedlings are planted, 
 water them to settle the soil. For late 
 plantings when sudden hot spells are ex- 
 pected, provide protection from the sun 
 by placing a shingle on the south side of 
 each plant. Irrigate the seedlings again 
 the day after planting. 
 
 Care of the nursery 
 
 After the seedlings are established, they 
 need irrigation every week to ten days. 
 The success of the nursery depends on 
 careful irrigation more than upon any 
 other operation. Examine the soil at fre- 
 quent intervals to make sure it never 
 becomes dry. This keeps the seedlings 
 growing without interruption and pro- 
 duces the most desirable type of seedling 
 for budding or grafting. 
 
 It is important to keep the nursery free 
 of weeds ; they compete with the seedlings 
 and retard their growth. Be especially 
 careful to keep noxious weeds out of the 
 nursery; otherwise, state regulations may 
 forbid moving the trees. 
 
 Fertilization is usually necessary. Use 
 1 pound of a chemical nitrogen carrier to 
 150 feet of nursery row avS needed. The 
 amount must be determined for each by 
 seedling color and vigor. Seedlings lack- 
 ing nitrogen are pale green to yellow and 
 grow slowly, if at all. Those with ade- 
 quate nitrogen have dark green leaves 
 and grow vigorously. 
 
 Except in cool coastal areas, most seed- 
 lings will be large enough to bud by fall 
 and the rest will be ready by spring. 
 
 [6 
 
BUDDED 
 
 nii~* 
 
 Budding the seedlings 
 
 Budding can be done in the fall or in the 
 spring as soon as the bark will slip. Bud- 
 ding may also be done during the sum- 
 mer but it is difficult to get a good stand ; 
 the eyes of the buds tend to fall out. 
 Seedlings should be at least % inch in 
 diameter where the bud is to be inserted 
 before budding. Discard those that have 
 not made vigorous growth or that show 
 diseased or ofTtype growth; they usually 
 produce poor trees. 
 
 Selecting suitable buds is the most dif- 
 ficult part of the job. Buds will be found 
 on mature terminal growth which is not 
 producing new growth. Those nearest the 
 terminal end are usually best. Select 
 plump dormant buds on mature wood. 
 For late summer or fall buds, select new 
 growth with fully expanded mature 
 
 leaves. For spring budding the best time 
 to obtain buds is in late winter before 
 growth begins. 
 
 Since varieties differ in growth habits, 
 only experience will enable one to select 
 the best buds for the various varieties. 
 Some varieties bear good buds at most 
 seasons. Others have acceptable buds 
 only during short periods. Buds cut be- 
 fore spring growth begins can be kept in 
 polyethylene bags at temperatures be- 
 tween 40° and 45° F for one or two 
 months. When suitable buds are located, 
 cut the leaves off % inch from the bud 
 and keep the sticks in moist burlap until 
 used or placed in storage. Always protect 
 them from drying. It is often best to em- 
 ploy a professional propagator to bud the 
 trees. This insures a good set of buds and 
 saves time and money. However, with a 
 
 Scions selected for budding. Left: Fuerte. Right: Haas. 
 
T 
 
 W 
 
 I 
 
 Budstick with 
 bud removed 
 
 T-cut 
 
 Bud 
 inserted 
 
 Bud tied 
 
 little practice most growers can bud suc- 
 cessfully. 
 
 When the seedlings are ready to bud, 
 use a sharp, thin-bladed knife with a 
 rounded point. Make a T cut in the bark 
 of the seedling at a smooth place, about 
 3 or 4 inches above the soil. The T cut 
 may be either upright or inverted. When 
 making the cut crossing the T, hold the 
 knife at an angle so as to raise the edge 
 of the bark slightly. This makes it easier 
 to insert the bud. 
 
 Next, cut a bud from one of the bud- 
 sticks with a single smooth stroke of the 
 knife. It is important to have the cut sur- 
 face smooth. If the upright T is used, start 
 about % inch below the bud and remove 
 a shield-shaped chip about l 1 /^ to 2 
 inches long. Cut deep enough to take a 
 sliver of wood under the bud. As the cut 
 is completed, hold the top of the bud 
 against the knife with the thumb and as 
 quickly as possible insert the bud down- 
 ward under the bark. Wrap all of the cut 
 surface but leave the eye of the bud ex- 
 posed. Various kinds of budding tape are 
 available but plastic materials are best. 
 
 The wrapping can be removed from 
 spring buds in about six weeks and from 
 summer buds in about four weeks. Fall 
 buds may be left eight weeks or more 
 before the wraps are removed. Always 
 remove wraps before the stock is con- 
 stricted. With fast-growing seedlings it 
 may be necessary to loosen the wraps in 
 about three weeks to prevent constricting 
 the stock. 
 
 At the time of budding or shortly there- 
 after, remove the tip of the rootstock 
 seedling. This will retard growth and 
 help force the bud. When the wraps are 
 removed, examine the buds to see if they 
 have taken. Successful buds will be green 
 and the bud or eye will be firmly in place. 
 If the bud has taken, cut the seedling 
 stock back to 10 inches above the bud to 
 force growth. 
 
 Staking 
 
 When the bud has grown about 6 inches, 
 tie it to the seedling stock for support. 
 Trees are sometimes dug at this stage 
 and planted in the orchards as tied-up 
 buds. 
 
 When the bud is ready for the second 
 tie, the trees should be staked, using lath 
 or 4-foot long, %- to %-inch redwood 
 stakes which are available for this pur- 
 pose. The buds grow rapidly and need 
 tying at frequent intervals. When the bud 
 has grown 12 or 14 inches the seedling 
 stock can be cut off close to the bud union. 
 This should be done not less than two 
 weeks before the trees are to be dug. Use 
 a coping saw or other fine-toothed saw. 
 Slant the cut down and away from the 
 bud union so that the scar will heal 
 quickly. Cover the wound with a good 
 pruning compound, such as emulsified 
 asphalt. Be careful to prevent all sprouts 
 on the rootstock from developing. Trees 
 can be dug any time after they are 18 
 inches high. 
 
 Digging the trees 
 
 Standard budded avocado trees are usu- 
 ally dug with a ball of soil about 10 
 
 [8 
 
inches in diameter and 14 to 16 inches 
 deep. A special balling spade is used. The 
 soil should be moist but not wet. Insert 
 the spade 5 inches from the tree trunk to 
 a depth of 14 to 16 inches on all four 
 sides. This will cut the roots on all sides 
 and make a ball 10 inches in diameter. 
 Next, remove the soil from one side of 
 the ball, leaving the balling spade in place 
 on the opposite side of the ball. Using a 
 shovel, cut the bottom of the ball 14 to 16 
 
 inches below the soil surface. Remove the 
 ball with the balling spade and lay it on a 
 piece of burlap or material suitable for 
 wrapping the ball. Burlap grain sacks are 
 commonly used; one sack will make two 
 wraps. Paper can be used if the trees are 
 to be planted immediately. 
 
 To tie the wrap slip the spade from 
 under the ball and fold the wrap around 
 the ball. Gather the wrap around the 
 trunk of the tree and tie it in place as 
 
 a. First cut on a budded seedling retards 
 growth and helps force bud. 
 
 b. Second cut on budded seedling gives 
 bud further nourishment. 
 
 * I - ;*.--.. 
 
close to the soil surface as possible. Next, 
 make three half-hitches around the ball 
 and pass the twine under the ball and up 
 the opposite side to the trunk where it is 
 then tied securely. Form the lower half- 
 hitch near the bottom of the ball to pro- 
 tect it from spreading when wet. The 
 tree is then ready to plant. 
 
 Always lift the ball from the bottom, 
 never by the tree. Trees can be handled 
 with less damage to the balls if they are 
 kept in a shady place and watered lightly 
 for several days. If trees are to be held for 
 some time after digging, the twine used 
 to tie the ball should be treated to resist 
 decay. 
 
 Growing tip grafts 
 
 Many avocado trees are produced by 
 whip-grafting (see illustration, p. 12) 
 seed I inn rootstocks when they are ap- 
 proximately ] /4 inch in diameter. This 
 kind of tree is known as a tip graft. 
 Field-grown seedlings can be tip grafted, 
 but this is not common practice. Tip 
 grafts are usually produced in a hothouse 
 where temperatures can be maintained 
 above 55° or 60° F. Some growers main- 
 tain a soil temperature of 70° or 80° by 
 means of bottom heat and pay little atten- 
 tion to air temperature. Trees can be 
 grown more rapidly by these methods. 
 Seed is planted as early in the fall as it 
 becomes available and the seedlings are 
 grafted in late winter or early spring. The 
 trees are usually ready to plant in the 
 orchard by spring or early summer. 
 
 In cooler areas where fruit matures 
 later and trees develop more slowly it is 
 often desirable to store seed from the pre- 
 vious season for summer planting. This 
 gives the seedling an early start so that 
 the trees will be ready for spring planting. 
 
 Tip grafts are also grown out-of-doors 
 or in lath or cloth shelters. Cloth shelters 
 are best because they exclude wind and 
 maintain more favorable temperatures. 
 Seed planted in late summer or early fall 
 will usually be ready to graft in spring 
 and the trees will be ready to plant the 
 following spring or early summer. 
 
 Since tip grafts are usually grown in 
 tar paper pots, greater control of soil- 
 borne diseases is possible through careful 
 
 i 
 
 choice of soil and the use of soil fumiga- 
 tion. Tip grafts require more care after 
 planting in the orchard but this is offset 
 by the lower initial cost and the reduced 
 hazard of soil-borne diseases. 
 
 Seedlings to be tip-grafted are usually 
 grown in individual open-bottom pots 
 made of 30-pound felt roofing paper. 
 Some growers prefer 40- to 60-pound 
 roofing paper. The most popular pot size 
 is 12 inches deep by 5 inches in diameter. 
 Pots are made by cutting the roll into 
 three 12-inch sections. These strips are 
 then cut into lengths to give the size of 
 pot desired. Eighteen-inch pieces make 
 5-inch pots. The pots are made by rolling 
 the pieces into cylinders, sealing the lap 
 with hot tar or stapling the seams to hold 
 them in place. 
 
 Some growers, especially those who 
 produce trees without artificial heat, cut 
 90-pound felt roofing paper rolls in half, 
 and make pots 13 inches deep and 6 
 inches in diameter to allow for greater 
 root development. Pots this deep tend to 
 buckle near the base unless given support. 
 This support can be provided by cutting 
 the top and bottom out of gallon tin cans, 
 slitting the side, wrapping them around 
 the pots and tying them in place with 
 wire. 
 
 It is important to choose soil for pot- 
 ting that has not been used to grow avo- 
 cados or other crops subject to cinnamon 
 root rot or verticillium wilt. It must drain 
 readily and remain in good condition 
 under frequent irrigation. It is a good 
 idea to pot some of the soil and see how 
 
 10] 
 
it works before making large-scale plant- 
 ings. A sandy loam is usually preferred. 
 Drainage can be improved by adding 
 peat moss, compost or well-rotted ma- 
 nure. (These materials sometimes contain 
 excessive amounts of salt and should be 
 checked for salinity before use. Avocados 
 are unusually sensitive to salty soils. Be 
 sure the soil has a low content of soluble 
 salts and always irrigate the pots to get 
 adequate leaching.) Clay loams can be 
 used to advantage if treated with a suit- 
 able soil conditioner. Krillium used at 1 
 pound to 500 pounds of clay loam soil has 
 given good results. 
 
 To fill the pots place about 2 inches of 
 moist soil in the bottom and tamp it 
 firmly so that it will not fall out when 
 the pot is handled. Then fill the pot to 
 within 1% inches of the top, making the 
 soil firm but not too compact. To keep 
 the soil in the pots from being contami- 
 nated by the cinnamon fungus, place 
 them on a plank bench. If there is no 
 infected soil in the area, gravel or sand 
 beds are satisfactory. It is often best to 
 fumigate the pots with a good fungicide 
 after they are filled and in place, treating 
 the whole bench. The seed may then be 
 planted directly in the pot, leaving the 
 tip flush with the soil surface. Because 
 avocado seed does not germinate uni- 
 formly some growers prefer to sprout the 
 seed in moist sand, moss or vermiculite. 
 This practice is especially desirable with 
 seed of questionable germination. (Care 
 must be used in planting sprouted seed 
 to avoid injury to the tender root.) It 
 insures more uniform development of 
 seedlings and simplifies their care. The 
 seed should be covered with % inch of 
 clean sand, vermiculite or other suitable 
 material to prevent drying and to keep a 
 crust from forming on the soil. After 
 planting the seed, irrigate at once. Ex- 
 amine the soil in the pots frequently and 
 keep it moist at all times. It is important 
 to keep the seedlings growing vigorously 
 without setbacks. 
 
 With most soils some fertilization will 
 
 be necessary after the seedlings are 4 to 
 6 inches high. A convenient method is to 
 dissolve % pound of a chemical nitrogen 
 fertilizer in 10 gallons of water and give 
 each pot % pint. One application is usu- 
 ally enough but it should be repeated if 
 the trees do not retain a good green color. 
 
 Grafting the seedlings 
 
 Seedlings are ready to graft when they 
 are about ^ inch in diameter. The size 
 must be determined by the scion wood 
 available; the seedling and the scion 
 should have about the same diameter. 
 Slow growing or offtype seedlings should 
 be discarded. Select wood for grafting as 
 described for budding but keep in mind 
 the size of the seedlings to be grafted. 
 
 To make the graft, cut the seedling off 
 3 or 4 inches above the soil, making a 
 smooth slanting cut about 1 inch long, 
 depending on the size of the stock. Next, 
 choose a piece of graft wood 2 to 3 inches 
 long, with at least one good bud. This is 
 called a scion. Make a sloping cut on the 
 base of the scion to match the cut on 
 the seedling stock. 
 
 A second cut is sometimes made on 
 both scion and stock. Begin about a third 
 of the way down from the tip of the stock 
 and the base of the scion make a cut a 
 third as long as the first cut. This cut is 
 not made with the grain of the wood but 
 is slanted somewhat across the grain 
 toward the first cut. This cut is not neces- 
 sary but it is convenient because it holds 
 the scion while it is being wrapped. 
 
 Fit the scion to the stock as illustrated 
 and wrap firmly with plastic tape. Seal 
 the end of the scion with asphalt emulsion 
 or other good grafting compound. Under 
 usual growing conditions the wraps can 
 be removed in four to eight weeks. Never 
 leave the wrap on long enough to con- 
 strict the growth of the tree. Tip grafts 
 are ready to plant in the orchard when 
 they are 12 to 18 inches high. Trees in 
 18-inch pots can be held until they are 
 larger. 
 
 Trees produced in a hothouse should 
 
 [in 
 
Scions for tip grafting. Left: scions selected for knuckles. 
 Right: scions selected for axillary buds. 
 
 A 
 
 y 
 
 A common 
 splice graft 
 
 •:4» 
 
 (* 
 
 Whip and 
 tongue graft 
 
 A tip graft. Note 
 slanting junction and 
 careful wrapping of 
 joined area. 
 
be hardened before planting. This can be 
 done by moving the trees to a lath house 
 or a location providing light shade. Allow 
 enough space so that the trees do not 
 
 shade each other. Planting can begin in 
 10 days or two weeks. After planting, the 
 trees should be staked and cared for in 
 the same way as standard nursery trees. 
 
 TOPWORKING 
 
 Avocado growers frequently have reasons 
 for topworking trees that are unprofitable 
 because of their low production or poor 
 fruit quality. If the trees are thrifty and 
 free of disease they can be topworked to 
 more desirable varieties. The resulting 
 trees are entirely satisfactory and will 
 come into production more quickly than 
 nursery trees put in as replants. Varieties 
 suited to the area will usually bear fruit 
 in two to five years after topworking. It 
 is not difficult to topwork avocado trees 
 but if a large number of trees are in- 
 volved an inexperienced person will usu- 
 ally find it less costly in the long run to 
 employ a commercial propagator. 
 
 Avocados can be topworked at any 
 time, but late winter or spring is best. 
 Grafts made at this time have a full grow- 
 ing season in which to develop before 
 winter. Late grafts are more susceptible 
 to cold injury. 
 
 The two methods of topworking most 
 commonly used for avocados are the bark 
 graft and the saw kerf or notch graft. 
 Some growers prefer to top the trees and 
 bud or graft into the vigorous shoots that 
 develop. This method is not commonly 
 used; it requires more time and is not 
 recommended. 
 
 Most propagators place the scion di- 
 rectly in the tree stump. Grafts can be 
 placed in the frame branches but this 
 requires more work and the sprouts are 
 difficult to manage. With avocados it is 
 not necessary to leave a nurse limb. 
 
 Trees to be topworked are cut off at a 
 convenient working height where the 
 bark is smooth. If there is a poor bud 
 union, or if for any reason the trunk is 
 damaged, the cut can be made below the 
 bud union. The trees are usually cut when 
 
 the grafts are placed but can be cut ahead 
 of time. Within a day or two after the cut 
 is made the bark begins to tighten and 
 will not slip again for several weeks. For 
 this reason if a bark graft is used the cut 
 is made at the time of grafting or four 
 to six weeks in advance. If the trees are 
 cut some time before grafting, a fresh cut 
 is made when the grafting is done. 
 
 After the tree top is removed, the bark 
 is susceptible to sunburn. On hot days 
 injury may result in a few hours. For 
 this reason the stump should be white- 
 washed or provided with other suitable 
 protection from sunburn immediately 
 after the top is removed. 
 
 Scions for topworking should be se- 
 lected from mature growth. Choose thick 
 wood with plump buds. Some propagators 
 prefer scions with a ring of buds, com- 
 monly called a knuckle, that develop 
 where growth was retarded between 
 flushes of growth. Avoid immature wood 
 near the terminal bud. Always protect 
 scion wood from drying. It can be stored 
 for several weeks in polyethylene bags at 
 temperatures of 40° to 45° F. 
 
 The bark graft 
 
 This graft is easy to make and can be 
 used at any time when the bark will slip. 
 In early spring the bark may not slip 
 until the buds are too far advanced for 
 grafting. For this reason, it is wise to 
 select scions for early bark grafting be- 
 fore spring growth begins and store them 
 until needed. The three most commonly 
 used methods are described below. 
 
 To prepare the stump, make a single 
 2V2-mch vertical slit in the bark at each 
 point where a scion is to be placed. On 
 small stumps there should usually be two 
 
 [13] 
 
scions and on larger ones the scions 
 should be placed at 4- to 6-inch intervals. 
 They may not all be needed but the\ will 
 keep the bark from dying back until the 
 scions selected to form the new tree are 
 ready to take over. 
 
 \\ocado bark is sometimes too thick 
 and stiff to fit snugly around scions. In 
 such cases it can be thinned around the 
 slits to about % inch. 
 
 The -(ions are prepared as illustrated. 
 A sloping cut 21/) to 3 inches long is made 
 on one side of the scion. Be sure the cut 
 surface is smooth so that it makes good 
 contact with the wood of the stump. It 
 may be desirable to make a second cut 
 about y<2, inch long on the opposite side 
 of the scion. This cut removes the soft 
 Hexible bark at the base of the scion and 
 makes it easier to insert without dam- 
 aging the bark. Leave at least two good 
 buds on the scion but do not make it un- 
 necessarily long. If too much of the scion 
 is exposed it may dry out and fail to take. 
 The scions are pushed down under the 
 bark, leaving only a little of the cut sur- 
 
 How to prepare scion for bark graft 
 
 Face toward 
 wood surface 
 
 Face toward 
 bark surface 
 
 Scions selected for topworking are 
 heavier than scions used for budding. 
 Bottom left: scions selected for knuckles. 
 Bottom right: scions selected for axillary 
 buds. 
 
face exposed. The cut surface must face 
 inward and fit close to the wood of the 
 stump. The scions are held in place by 
 several turns of stout tape or by driving 
 one or two flat-headed nails through the 
 scion into the stump. The bark may be 
 held in place by a nail on each side of 
 the scion. Number 19 and 20 nails are 
 usually about right; nails are preferred 
 on very large stumps. 
 
 A slightly different way to make a bark 
 graft is used by some propagators. The 
 bark is slit and the scions are prepared 
 as described above. The scion is then 
 inserted by raising the bark on one side 
 of the slit only. This gives close contact 
 between one side of the scion and the 
 undisturbed bark of the stump. The scion 
 is nailed or tied in place. 
 
 A third method is also used. The scion 
 is prepared as before. Then two slits are 
 made just far enough apart to admit the 
 scion without raising the bark. The 
 tongue of bark between the cuts is raised 
 and the scion is inserted. The tongue of 
 bark remains on top of the scion. The 
 
 Bark graft. Left: thinning bark. Right: inserting scion into vertical cut in bark. 
 
 [15] 
 
 ' 
 
scion is held in place by two nails driven 
 through the tongue of bark and the scion 
 into the wood of the stump. 
 
 As soon as possible seal the upper end 
 of the scion; next, seal the cut surface of 
 the stump and cover the thinned bark. 
 I se an asphalt emulsion, grafting wax or 
 any good grafting compound for this pur- 
 pose. Some materials shrink and crack 
 after a time so it is a good idea to check 
 the work in 10 days or two weeks and 
 seal any cracks that may develop. As an 
 added protection in warmer areas, some 
 propagators cut a circular piece of white 
 paper and place it over the cut surface of 
 the stump to reflect the heat and protect 
 the scions from sunburn. 
 
 When the scions are in place, tie or nail 
 three or more light sticks to the stump 
 so that they extend about 12 inches above 
 it. Then place a paper sack over the end 
 of the stump, using the sticks as a sup- 
 port. Tie the sack to the stump and tear 
 a few holes in it to prevent accumulation 
 of excessive heat. Whitewash or shade 
 the trunks promptly to protect the bark 
 from sunburn, as a few hours' exposure 
 on a hot day will cause damage. 
 
 Another way to protect the grafts is to 
 wrap heavy white butcher's paper around 
 the stump, extending it a foot or more 
 above the stump. The larger the stump 
 the higher the paper must extend above 
 it. When tied firmly in place, the paper 
 is supported with three or more thin 
 sticks pushed down vertically between it 
 and the stump. Draw the top together and 
 pin it with nails, leaving openings to 
 admit light, prevent accumulation of 
 heat, and to permit the scions to grow out 
 into the light without further attention. 
 
 When the scions begin to grow, enlarge 
 the openings in the sack or paper to let 
 in more light. When scions are about 6 
 inches high, tear the bottom or upper 
 part off the sacks, or if paper is used, open 
 the upper end and let the scion grow out 
 into the light. Leave the paper or sack in 
 place to shade the top of the stump until 
 the scions provide adequate shade. 
 
 Instead of paper shading, a latex-base 
 white paint can be used for protection 
 from sunburn. When the grafts are in 
 place, cover all cut surfaces with asphalt 
 emulsion. As soon as the surface of the 
 emulsion is dry, apply a coat of latex- 
 base white paint. The scions and buds 
 should also be covered with white latex 
 paint for further protection. This treat- 
 ment reduces damage to the buds by 
 mealybugs and worms which often flour- 
 ish within the protection of paper bags 
 in the coastal areas. Use only water- 
 thinned polyvinyl latex-base white paint. 
 Paints which contain oils, thinners, or 
 turpentine injure the stump and usually 
 kill the scion. 
 
 Notch graft 
 
 The saw kerf or notch graft requires 
 more skill than the bark graft but it can 
 be made at any time of the year because 
 it is not necessary to have the bark slip. 
 A single cut is made with a saw for each 
 scion. The cut should extend inward 
 about 2 inches on the cut surface of the 
 stump and down the side about 3 inches. 
 With this method it is especially impor- 
 tant to choose thick, well-matured scion 
 wood with a greater diameter than that 
 used in a bark graft. The scion is pre- 
 pared by making a sloping cut 2% to 3 
 inches long on each side to make a wedge 
 with one side thicker than the other. The 
 saw cut is then widened to fit the scion. 
 Most propagators prefer a wide chisel or 
 a sharpened putty knife with the bevel 
 on one side for this purpose. The thick 
 side of the scion faces outward and the 
 scion is driven into the notch so that the 
 cambium of the scion matches the cam- 
 bium of the stump. The cambium is a 
 thin layer of cells between the bark and 
 the wood of both the stump and scion. 
 These are the cells that produce growth 
 and it is for this reason that the two 
 cambium layers must be brought together 
 in placing the scions into the cut in the 
 stock. Because of differences in thickness 
 of bark the scion will not be flush with 
 
 [16 
 
Saw kerf or notch graft. Left: sawing the notch. Right: widening the notch with 
 a chisel (or specially prepared putty knife) and inserting scion. 
 
 the bark of the stump. The scion may be 
 placed at a slight angle to insure that the 
 two cambiums make contact at least at 
 one point. The scion does not need to be 
 nailed or tied but it is a good idea to wrap 
 the top of the stump with tape to protect 
 the upper edge of the bark. The scions 
 are sealed and the stump prepared as 
 described previously. 
 
 Scion for 
 kerf graft 
 
 £=^ 
 
 outside edge must 
 be thicker than 
 the inside edge ' 
 
 Care of the grafted tree 
 
 The new sprouts will need support for 
 several years to prevent the wind blowing 
 them out. One or more stout stakes ex- 
 tending 4 or 5 feet above the top of the 
 stump provide such support. Except with 
 small trees it will be best to nail the 
 stakes to the stump. As the new shoots 
 develop they should be tied at frequent 
 intervals. Use soft twine and tie them 
 loosely. 
 
 Pinch back growth from the old stump 
 so that it never shades or interferes with 
 the scions. When the scions are about 
 2 feet tall, select the best graft to make 
 the new tree. It should have a strong 
 union with the stump and it will be less 
 likely to be blown out if it is on the wind- 
 ward side. All other scions should be re- 
 tained but they should be pinched back 
 occasionally so that they do not interfere 
 with the growth of the new trunk. The 
 extra grafts can be used to replace the 
 main graft if it is accidentally broken off. 
 This growth which shades the stump and 
 keeps the bark from dying back should 
 be eliminated gradually as the new tree 
 develops. 
 
 In windv areas it is often desirable to 
 
 [17] 
 
graft two or three scions together. After 
 they have grown enough (12 to 18 
 inches) so that they can be drawn to- 
 gether, select two or preferably three 
 scions from opposing sides of the stump. 
 Slice a 2%- to 3-inch strip of bark with 
 a little wood off the side of each scion in 
 a position so that the cut surfaces can 
 be brought together. Bind the scions 
 firmly together with budding tape, mak- 
 ing sure their cambium layers touch each 
 other. When the scions have grown to- 
 gether, select the strongest one to make 
 the new tree and pinch the others back 
 so that they will not interfere with its 
 development. Do not remove the wrap- 
 ping until the union is strong. It may be 
 
 necessary to loosen it occasional!} to 
 avoid constricting growth. 
 
 Ample moisture must be provided, but 
 since the top has been reduced the tree 
 will use less water than formerly. It is 
 important to avoid over-irrigation fol- 
 lowing topworking operations. 
 
 Fertilization is not usually needed until 
 a new top has been established. The new 
 top will need some training as it develops 
 but unnecessary pruning will delay fruit- 
 ing. The principal need is to prevent 
 upright-growing varieties becoming too 
 tall. As far as possible this should be done 
 by pinching new growth back before it 
 gets out of bounds. If the tree becomes 
 too tall, cut it back to a lateral branch. 
 
 Avocados can be grown from cuttings, 
 but the resulting plants are more difficult 
 to handle than are those on seedling root- 
 stocks. Trials have shown that there is no 
 particular advantage in this method of 
 propagation so far as fruit production is 
 concerned. Since most varieties are diffi- 
 cult to root by cuttings, it is doubtful that 
 this method will replace the use of seed- 
 ling rootstocks for commercial propaga- 
 tion. 
 
 Propagation by cuttings has the ad- 
 vantage of making it possible to produce 
 genetically identical rootstocks or trees, 
 in contrast to the wide genetic variation 
 found in seedlings. Thus, the cutting 
 method would provide a means of multi- 
 plying superior rootstocks, if such root- 
 stocks are developed. 
 
 Some varieties can be rooted by ordi- 
 nary methods; others require special 
 treatment. Among those that root easily 
 are Zutano and Ganter. Fuerte can be 
 rooted but results are only medium to 
 
 poor. The Duke, Mexicola, and Topa 
 Topa, and all Guatemalan varieties are 
 very difficult to root. Some rootstock 
 suckers are readily rooted, but others are 
 difficult. Varieties that root most readily 
 can be rooted under mist or in an ordi- 
 nary cutting box where humidity can be 
 held at saturation. 
 
 To make cuttings, select mature termi- 
 nal growth. Make the cuttings 3 to 6 
 inches long, with three or four leaves on 
 each cutting. Bottom heat is beneficial. 
 70° F gives good results but the best 
 temperature has not been determined. 
 Any of the common rooting media can be 
 used, provided drainage is good. It takes 
 two to four months to root the cuttings 
 and to grow enough roots to permit trans- 
 planting. The rooted cuttings are trans- 
 planted to pots and handled as other 
 trees. They must be hardened by slowly 
 reducing the humidity. This can be done 
 either in the cutting bed before trans- 
 planting or after transplanting to pots. 
 
 L8 
 
For varieties that are difficult to root 
 it is necessary to grow a shoot the base 
 of which has never been exposed to light. 
 This is accomplished by first budding or 
 grafting the variety to be rooted onto a 
 suitable stock, preferably in a small pot 
 or a 1-quart can. If grafted plants are 
 available they can be cut back near the 
 graft union. When buds on the scion start 
 to grow, these buds are covered to a depth 
 of 2 or 3 inches with vermiculite or a 
 mixture of peat and sand. This can be 
 held in place by a cylinder of black build- 
 ing paper or by a cylinder of tin. The 
 new shoots are then allowed to push 
 through this medium and develop three 
 to five leaves in the light. The same results 
 can be obtained by covering the stub with 
 an inverted tin can or by placing the 
 plant in a dark chamber. After the new 
 shoot has made 2 to 4 inches of growth 
 in the dark, it must be surrounded, as 
 
 described, with vermiculite or peat and 
 sand. 
 
 The tip of the new shoot is then allowed 
 to develop normal leaves in the light 
 above the covering medium. When three 
 to five leaves have developed, the shoot 
 can be detached at its junction with the 
 original stem and rooted as described 
 above. It can also be rooted in place by 
 girdling at the base of the shoot to be 
 rooted and surrounding it with moist 
 rooting medium. It is sometimes possible 
 to grow and root two to four shoots from 
 a single plant at one time. Four to eight 
 weeks are required for roots to appear. 
 
 When the shoots are removed for root- 
 ing, additional shoots usually develop and 
 the process can be repeated. It is often 
 possible to use the same plant twice, and 
 vigorous plants may be used as many as 
 five times. 
 
 15m-l,'65(E9786)L.P. 
 
Well, not exactly — you can't grow auto- 
 mobiles on farms, but farm products are 
 essential in manufacturing them. Consider 
 the annual agricultural needs of just one 
 major automobile company. 
 
 900,000 bushels of corn 
 
 736,000 bushels of flax- 
 seed 
 
 74,000 bales of cotton 
 
 or, in terms of approximate acreage: 
 
 15,000 acres of corn 
 
 80,000 acres of flax 
 78,000 acres of cotton 
 
 During the same period this company used products derived from 
 364,000 sheep and 36,000 cattle — plus many other items such as hog 
 bristles and beeswax. In all, produce equivalent to the output of 1,000 
 good-sized farms is needed yearly. No wonder a top executive in the 
 automotive industry has said: "Our plants, here and throughout the 
 world, would have to close their doors in a few days if their flow of 
 agricultural materials were to stop." 
 
 Supplying America's countless industries — and feeding the nation 
 bountifully — makes agriculture America's biggest and perhaps most 
 important business. That is one reason why anything which affects 
 agriculture affects everybody.