Fruit tree thinning
Want the best fruit? Think about thinning your fruit trees.
Fruit trees often set more fruit than they can support or develop adequately, especially if the trees were not properly pruned during the previous season, Excessive fruit compete with each other for carbohydrates (stored energy) and remain small. This carbohydrate drain, or “sink" can also weaken the tree and make it more susceptible to pests and sunburn damage. Leaving too much fruit on a tree can also lead to alternate bearing (a cycle in which the tree bears excessively in one year and little the next year) or limb breakage. Thinning the fruit helps prevent these problems from developing.
Species That Require Thinning
All stone fruits (peaches, apricots, nectarines, cherries, plums, etc.) require thinning. Of pome fruits, all apples and Asian pears as well as most European pears require thinning. Bartlett pears often thin themselves, and harvesting larger fruit early (early to mid-July) allows the smaller fruits to increase in size for a second pick 1 to 2 weeks later.
Timing of Thinning
Fruit should be thinned when they are fairly small, typically from early April (for early-ripening fruit) to mid-May (for late-ripening fruit). Stone fruits are thinned when they are about .3/4 to 1 inch in diameter, and pome fruits (apples and pears) are thinned at l/2 to 1 inch, or within about 30 to 45 days after full bloom. Thinning too early can result in split pits in stone fruits, especially peaches; thinning too late reduces the chances that fruit size will increase.
How Much Fruit to Thin
The amount of fruit to thin depends on the species and the overall fruit load on the tree. For example, stone fruits such as apricots and plums are fairly small, so they should be thinned to 2 to 4 inches apart on the branch. Peaches and nectarines should be thinned to about 3 to 5 inches. If spring conditions for pollination were ideal, excessive fruit may have set, requiring even more thinning. If the fruit load is light, but one or two branches have a large amount of fruit, less thinning is required because the total number of fruit is low.
Unlike stone fruits, which produce one fruit per bud, pome fruits (apples and pears) produce a cluster of flowers and fruit from each bud. Thin to no more than one to two fruit per cluster, depending on the total fruit set and growing conditions. Retain the largest fruit whenever possible. When the crop is heavy, fruit should be spaced no less than 6 to 8 inches apart.
Methods of Thinning
There are two main ways to thin fruits: by hand or by pole. Thinning by hand is more thorough and accurate than the pole method, but it is much slower.
Hand-thinning involves removing enough fruit to leave the remaining fruit with sufficient space so they do not touch at maturity. On short spurs, this may mean leaving only two or three fruit per spur. If a long branch produces fruit on its entire length, thin more heavily, especially near the terminal end. Remove "doubles" (two fruit fused together) and small, disfigured, or damaged fruit when you have the option. Many times, it is possible to leave more fruit by selecting those on alternating sides of the branch.
Pole-thinning is used mainly on large trees where hand-thinning would be cumbersome or impractical. Pole-thinning is much faster, and although it is less accurate, the results are often acceptable. Attach a short rubber hose, cloth, or thick tape to the end of the pole to reduce scarring or bruising of branches. Strike individual fruit or clusters to remove a portion of the fruit. With experience, you will be able to strike a cluster once or twice with just enough force to adequately break up the cluster.
Original ANR publication by CHUCK INGELS, University of California Cooperative Extension Farm Advisor, Pomology, Viticulture, and Environmental Horticulture, Sacramento County; PAMELA M. GEISEL, University of California Cooperative Extension Farm Advisor, Environmental Horticulture,
Fresno County; CAROLYN L. UNRUH, University of California Cooperative Extension
Fresno County staff writer; PATRICIA M. LAWSON, illustrator.
Edited for use on the Marin Master Gardener website by N Londeree, 3/12