An abundance of water is especially important during the first two or three years after the tree is planted, if rapid healthy growth is to be maintained. In Florida, particularly in sections where the soil is deep, many young groves have in the past suffered for lack of water. One of the most experienced growers near Miami states that trees which have had abundant irrigation are as large at four years of age as non-irrigated trees at six years. Their larger size enables them to yield commercial crops earlier than non-irrigated trees.
In California it is the general practice to irrigate avocados in the same manner as citrus fruits. The amount of water necessary for maximum development varies considerably on different soils, but during the first few years a thorough irrigation every ten days during the dry season is not too much.
The importance of an abundance of moisture in the soil at the time the fruit is setting has already been mentioned in the discussion of the climatic requirements of the avocado. Several crop failures in Florida have been blamed on unusually dry weather during this period. A drought probably does little harm if it occurs when the trees are just beginning to bloom, but if it continues the flowers are likely to drop and the crop to be a failure. This has been the experience with Trapps when grown on deep sand; on heavy soils, which are more retentive of moisture, the danger is less.
In order to avoid crop failures from this cause, the grower should certainly be prepared to irrigate at the time the fruit is setting. In southern Florida this is usually in March and April. When a prolonged dry spell occurs just at this time, as is sometimes the case, two or three thorough irrigations, a week apart, may suffice to save a considerable amount of fruit.
In California, if the soil is allowed to become too dry during the hot summer months, young trees are frequently given a setback from which they are slow to recover. This has been observed in Florida as well, particularly on deep sandy soils.
The method of applying water varies in different regions. In California the basin system is commonly used, especially when the number of trees to be irrigated is small. Basins should be filled with coarse strawy manure to serve as a mulch. In many orchards the trees are irrigated by the furrow system which is used with citrus fruits, the soil being cultivated after each irrigation. In southern Florida other methods are made necessary by the fact that water cannot be run in furrows over the sandy soil. Revolving sprinklers, placed at the proper distance so that all the ground will be covered by their spray, are sometimes employed. Where economy of water is a factor, these are less desirable than the basin system. Taken in all, it seems that the best method of irrigating is to form around the tree a basin as wide as the spread of the branches (or wider during the first two years), to fill it with weeds, straw, manure, seaweed, or other loose mulch, and then to apply water at least once in two weeks when the rainfall is not sufficient to maintain the tree in good growing condition.