Alternate Bearing and Hand Thinning of Tree Fruits

The tendency of fruit trees to bear fruit in two-year cycles, consisting of a large crop followed by a small crop, is termed alternate or biennial bearing. Alternate bearing occurs in almost all tree fruits. 

 
The flowers that produce next year's crop are initiated during the development of the current season's crop. When a fruit tree is producing a large fruit crop, most of the tree's energy is utilized for fruit development, little energy remains for flower initiation. As a result, a fruit tree often produces a small number of flowers and fruits when preceded by a heavy crop the previous year. 
 
To discourage alternate bearing, home gardeners should thin apple and other fruit trees when fruit set is heavy. Thinning also promotes the development of large, high quality fruit at harvest and prevents limb breakage on trees heavily laden with fruit. 
 
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 will generally thin themselves.
Issue: 
Category: 

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on June 1, 2011. The information contained within may not be the most current and accurate depending on when it is accessed.