City Fruit | Grow: Thinning

This article is excerpted from the Fruit Handbook for Western Washington: Varieties and Culture by G.A. Moulton and J. King. WSU Northwestern Washington Research and Extension Center (Mt Vernon, WA).

A tree doesn’t need all the fruits it produces: if only five percent of the blossoms on a tree grew into fruit, it would be a full crop.

Thinning is the process of removing some of the fruits on a tree so that the remaining fruits will grow larger. Removing some fruits—especially when cells are dividing rapidly—means that the remaining fruits have more cells—and will get larger.

Other advantages of thinning fruit

Thinning fruit can make the tree more productive in the following year because the immature fruit contains a hormone that inhibits the formation of fruit buds. Removing some of this immature fruit allows for more fruit buds the following year. Thinning also helps even out the crop load from year to year. Trees can get into a cycle of alternate bearing, overloaded with fruit one year, and producing low yields the following year. In a heavy bearing year, removing half or more of the blossom clusters at bloom time can help reduce this problem.

When to thin

Early thinning is better. In the month or so after fruit blossoms are pollinated, the newly set fruit undergoes rapid cell division and growth. Since the total number of cells determines the potential size of the fruit, thin fruit early so that the remaining fruit will have more cells – and can grow larger.

How to thin

Remove the smaller fruits and leave the larger ones: small fruit have fewer cells and will remain relatively small, even after thinning. Remove fruit with disease spots, hail damage or other defects. Aim for even spacing. Imagine what size the fruit will be at maturity and leave enough room so that fruits won’t crowd each other along the branch.

Grow Fruit

Overview
General Care
Pests & Diseases
Planting Fruit Trees
Pollination
Pruning
Fruit Varieties
Thinning
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Quick Reference Guides

Apples, Pears,

& Asian Pears

Apple and pear trees almost always need heavy thinning. Apple varieties that bear heavily year after year can be thinned at the bloom stage. The ‘king’ bloom, in the center of the blossom cluster, is the first to open, and it produces the biggest fruit. Remove all other flower buds on that spur. After the fruit has set, check back and thin again where the spurs are too close together. A good spacing for apples and pears is one fruit per 6” of branch. Asian pears should be spaced at one per 6 – 8”.

Plum & Peach

Peaches should be spaced at one fruit per 6 – 8”, and fruits that are joined should be removed. Plums, especially European plums such as Stanley or Italian plums, need thinning when the fruit set is heavy. They can be spaced closer than apples and pears, depending on the size of the fruit.