Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Fruits such as apples are prone to alternate bearing. A heavy crop as seen above may lead to a light crop the next year.
Biennial or alternate bearing refers to the tendency of perennial fruits to put on a heavy crop one year and then little or no fruit the second year. This is most common in tree fruits such as apples.
Next year’s flowers are initiated this year. If there are too many fruits on the plant in the current season, most of the energy goes to fruit development and less to flower initiation for next year. As a result, a fruit tree often produces a small number of flowers and fruits the year after a heavy crop.
Alternate year bearing is often variety related, so choose varieties that do not have alternate bearing habits when possible.
The main tool that we use to prevent alternate bearing is fruit thinning. Apples are commonly chemically thinned during bloom. If the chemical thinning was incomplete, hand thinning may be required if fruit loads are too high. In peaches, fruit thinning starts with dormant pruning to remove fruiting wood in vigorous varieties. This is followed by mechanical blossom thinning and the hand thinning to reach the optimal fruit load.
Hand thinning of apples should be done within six weeks of full bloom. Leave the largest apple in a cluster unless it is damaged. After thinning, apples should be spaced about 8 to 10 inches apart on the branches. Pears, apricots, and peaches may also need to be thinned. Fruit should be spaced 6 to 8 inches apart on the branches. Plums and cherries will generally thin themselves.