In Florida it has been the custom to bud or graft West Indian varieties on seedlings of the same race. In California the Guatemalan race has usually been budded on the Mexican, in the belief that the superior hardiness of the latter would make the budded tree less susceptible to cold and also because seeds of the Mexican race are more easily obtainable. Recently in Florida the Guatemalan has been budded on the West Indian, the West Indian on the Mexican, and so on ; and these experiments, although not extensive, have served to indicate that the question of stocks is of great importance, and demands further investigation. Not only does it appear that the hardiness of the tree may in a measure depend on the nature of the root stock, but the congeniality of the various races, when budded on each other, seems to differ. Attempts to bud the West Indian on the Mexican have produced rather indifferent results in Florida, the buds making a poor union and growing very slowly. The Mexican race has not been tried on the West Indian extensively, but this practice appears to succeed better than the reverse. The Guatemalan buds well on the West Indian, but is perhaps preferable on Guatemalan roots.
Seeds are usually obtainable most abundantly in August and September in Florida, a month or two later in California, having reference to the West Indian race in the former state and the Mexican in the latter. These two races are those generally used for seedling stocks. The seeds should be planted soon after removal from the fruit, although they are viable for several weeks if kept cool and dry. Seeds of the Mexican race have even been kept for three or four months in good condition, in the dry climate of California.
Previous to the issuing of Quarantine Order No. 12 of the Federal Horticultural Board, prohibiting the importation of avocado seeds from Mexico, many thousands were imported annually to California from that country. In shipping these, the best results were obtained when the seeds were removed from the fruit, washed immediately, dried in the shade, and packed loosely in wooden boxes without the addition of moistened sawdust, charcoal, sphagnum moss, or other material. The percentage of loss with such seeds was insignificant. When shipping seeds from moist tropical regions, greater difficulty is experienced, decay being more troublesome. Good results are sometimes secured by shipping in slightly dampened charcoal, but where the distance is not too great the best method seems to be to wash and dry the seeds and then pack them loosely in wooden boxes, as above described.
Seeds are planted in pots, boxes, flats, or in the open ground. For nursery work on a large scale, planting in flats and seedbeds has given excellent results. The seedlings are transplanted almost as soon as they have sprouted. In California seeds planted in the seed-bed during autumn, October to December, will make plants six to twelve inches high by March or April, when they may be planted out in the field in nursery rows.
While seedlings are sometimes budded in pots or boxes, field budding is more satisfactory, as it is difficult to bring pot-grown trees into the vigorous growth essential to success in budding.
Planting in the field should be done in California as soon as danger from frost and cold weather is past. Nursery rows should be 3 to 4 feet apart, with the plants 18 inches apart in the row (or about 12 inches in Florida). Partial shade should always be given the young plants for a few days after they are set in the open, especially if they have been sprouted, as they should be, under a lath- or slat-house. In Florida, seeds planted in August may be set out in the field in November, and should make trees ready to bud by January or February, which is the proper season for budding in that state.
For germinating seeds, a light, loose, sandy loam is preferable, pure sand sometimes being used in California if the seedlings are to be transplanted as soon as they have germinated. Four-inch pots are large enough for seeds of the Mexican race, but frequently a five- or six-inch pot is necessary to accommodate the West Indian. In Florida, wooden boxes about 6 inches in each dimension are often used, while in California tin cans are employed, but the latter are much less desirable than clay pots. When planted in flats or seed-beds, the seeds may be placed close together. The pointed end of the seed, - or in the case of round seeds, the end which has been toward the stem in the fruit, - should be uppermost, and it is usually allowed to project above the surface of the soil, not more than four-fifths of the seed being below the surface. If the seed-coats are loose and come off easily, it is well to remove them before planting.
The soil should be kept moist while the seeds are germinating. The time required for germination varies greatly, sprouts sometimes appearing within two weeks from planting, while in other instances they may be two or three months in starting. A month is the average time in warm weather.