This section is from the book "Manual Of Tropical And Subtropical Fruits", by Wilson Popenoe. Also available from Amazon: Manual Of Tropical And Subtropical Fruits.
The climatic requirements of the loquat, except as an ornamental plant, are distinctly subtropical. It is not successful in the hot tropical lowlands, nor can it be grown for fruiting purposes in regions subject to more than a few degrees of frost. Cool weather during part of the year and a rainfall of 15 to 50 inches (with artificial irrigation where the dry season is severe) suit it best. These conditions are found in southern Japan, in parts of southern California, along the shores of the Mediterranean, and in several other regions. It has been noted in Japan that the best loquat situations always lie close to the sea; and in California much finer fruit has been produced near the coast than in the foothill tracts twenty to thirty miles inland. Thus it seems that the mild climate of the seacoast is peculiarly favorable to the development of the fruit.
While mature trees have withstood temperatures as low as 10° above zero without serious injury, the flowers and young fruits may be killed by temperatures only a few degrees below freezing; hence loquats cannot be produced successfully where heavy frosts may occur at the time of flowering. Condit notes: "Frost coming when the fruit is less than half grown may result in killing the seeds only, while the flesh continues to develop, so that seedless fruits mature. On the other hand, frost may have somewhat the same effect as sunburn, injuring the tissues and causing them to shrink or to develop irregularly."
When grown in regions where the weather during the ripening season is extremely hot and dry, the fruit is subject to sun-scald or sunburn. The exposed surface withers and turns brown, and the product is rendered unfit for market. If, on the other hand, the weather is cool and foggy during the ripening season, the fruit lacks sweetness and flavor.
Sandy loam is considered the ideal loquat soil, and it should be of good depth. Several other types of soil have proved satisfactory; thus, in southern California good orchards have been produced on heavy clay of the adobe type, and in Florida the shallow rocky soils of the Homestead region on the lower east coast have given excellent results. Deep sandy soils, when of little fertility, are not suitable. Frank N. Meyer points out that the best loquat orchards in China are situated on low, rich, moist land.
In California orchards, loquat trees are planted 12 to 24 feet apart. When planted on the square system, they should not be nearer than 20 feet. Close planting has been practiced in Orange County, where the rows are set 24 feet apart and the trees 12 feet apart in the row. This is believed to result in greater regularity and uniformity of production than wider planting. March and April are good months for planting in California; late September and October are also suitable. In southern Florida the best time is probably in the autumn.
The amount of tillage given the orchard varies in different regions. Condit says: "Clean culture may be practiced throughout the season, but the growth either of a winter or a summer leguminous cover-crop is much more advisable." For a winter cover-crop, the natural vegetation which springs up in California with the arrival of the rains may be allowed to grow until it reaches its maximum development, when it should be cut with a mowing-machine and plowed under after the fruit is harvested. Following this the ground should be cultivated and a summer cover-crop such as buckwheat or the whip-poor-will cowpea should be planted. "Winter cover-crops may be planted as early as September, in which case they may have made sufficient growth to be turned under before the harvest begins. This is not always possible, especially if an early variety of loquat is grown; in fact, it is a question whether it is advisable to plow or work the ground deeply or at all during the setting and maturing of the fruit." In Florida and other regions different methods of cultivation may be required, but the liberal use of green cover-crops seems universally desirable.
In addition to cover-crops, stable manure is often used to enrich the land in California orchards. Bearing loquat trees exhaust the fertility of the soil rapidly and it is necessary to replenish the supply of plant-food annually if fruit of large size is to be expected. Condit observes: When the average California soil begins to fail from heavy production, nitrogen is likely to be the first crop limiter; after nitrogen, phosphoric acid, and after phosphoric acid, potash." Particular care should be taken, therefore, to see that the supply of nitrogen is sufficient to meet the demands of the tree. C. P. Taft, of Orange, California, has found the green cover-crops of great value in this connection. E. Pillans, Government Horticulturist at the Cape of Good Hope, says that a yearly application of well-rotted stable manure is amply repaid by larger crops and increased size of fruit. The loquat groves of Japan are said to be fertilized with litter, weeds from the roadsides, and, recently, with commercial fertilizers. Condit advises the application of 15 cubic feet of stable manure biennially to each bearing tree.
It is ordinarily considered that the amount of water required by loquat trees corresponds closely to that needed by citrus fruits. Probably it would be more accurate to say that the loquat is more drought-resistant than any of the citrus fruits, but that the best results are obtained when the orchard is irrigated as liberally as the citrus orchard. In California there is usually abundant rainfall at the time the fruits are approaching maturity; in other regions, or in California if the season is abnormally dry, it may be desirable to supply water at this time, since the fruits only develop to large size when there is abundant moisture in the soil. In southern France the tree is said not to do well on soils which are over-moist in winter.
The young tree should be headed 24 to 30 inches above the ground, and three to five main branches forced to develop. The loquat is a compact grower, and the mature tree requires much less pruning than most of the temperate-zone fruits. It has been found by C. P. Taft, however, that a certain number of branches must be cut out from time to time, in order to limit the amount of fruiting wood and to admit light to the center of the tree. It must be remembered that the tendency of the loquat is to overbear, and for the production of commercially valuable fruit this must be checked by pruning and thinning. The best time for pruning is soon after the crop has been harvested.