The amount of pruning required by the avocado depends largely on the variety. Some make short stocky growths and form shapely trees without the assistance of the pruning-shears, while others take long straggling shapes and do not branch sufficiently to form a good crown. These latter must be cut back heavily. Trapp, and other varieties of the West Indian race in general, usually make low stocky trees, branching abundantly and forming plenty of fruiting wood. With such forms, pruning is reduced to the minimum, consisting principally in removing fruit-spurs which die back after the crop has been harvested, and in the occasional cutting back of a branch to produce a crown of symmetrical form and good proportions. Beyond this very little pruning is done in Florida orchards.
With the Guatemalan race, more training is often necessary to produce a tree of ideal proportions, since some varieties tend to make long unbranched growths. In others the lateral branches are very weak and scarcely able to bear their own weight if allowed to develop unhindered. With these, careful attention should be given during the first few years to producing a well balanced tree capable of carrying good crops of fruit.
The Mexican race usually shows a tendency to grow more stiffly erect than the others, and make stout rigid branches which are capable of bearing heavy crops. In order to keep some of these varieties from becoming too tall and slender, it is necessary to top them when young, perhaps pinching out the buds of the main branches later on to induce branching.
It is not desirable to have the crown so dense that light will not reach all parts freely. When the crown is too thick, fruit is produced only on its outer surface, and much of the fruit-bearing capacity of the tree is thus wasted.
Thus it can be seen that no specific rules for pruning, covering all varieties, can be laid down, other than that the object should be to produce a tree having a broad, strong, well-branched crown of good proportions and great fruiting capacity, preferably headed low (about 30 inches above the ground), in order to shade the soil beneath it. After the tree has reached maturity little pruning is required, provided it has had the benefit of careful training during the first few years. Experience along this line is meager, however, and the future will bring out many new points of importance.
In top-working old seedlings, it is often necessary to cut off large limbs. The stubs should be smoothed off and covered with a coating of grafting-wax. The same rule applies to cuts made in the course of ordinary pruning with young as well as old trees. When secondary branches are removed, they should be cut as close to their junction with the main branch as possible, and the cut should be parallel with the main branch. The cut surface should be treated with a coating of grafting-wax. Paint is sometimes used for this purpose, but in Florida it has been found injurious, especially to young trees. If the stubs are not waxed, they often allow fungi to start and destroy the wood. The entrance of such fungi is facilitated by the fact that the pith sinks in the cut ends of large limbs, leaving a small cavity to collect water and maintain the moist conditions which are so favorable to fungous growth.
Opinions differ as to the best time for pruning. In Florida late fall and winter, November to February, have proved suitable. In California the best growers seem to favor spring or fall. According to Krome, pruning in hot weather often results in serious injury. The most favorable times seem to be early spring, before growth has commenced and before the heat of summer, and autumn after hot weather is past.