- Author: Ed Perry
When you remove young fruit from a limb, the remaining fruits benefit from the reduced competition for mineral nutrients, light, water and plant foods produced by the leaves. By thinning early, you also increase shoot and leaf growth. This results in extra leaves that produce more sugars and other materials necessary for sizing the remaining fruits. Thinning also helps prevent limb breakage caused by heavy crops.
You already thin fruit when you prune your trees, since nearly every pruning cut removes some flower buds. In fact, pruning is the only practical way of thinning cherries and nut crops. However, it is still necessary to hand thin stone fruits such as apricots, nectarines, peaches and plums and pome fruits such as apples and Asian pears. Species that rarely need hand thinning are almonds, avocados, bushberries (such as Boysenberries), cherries, citrus, European pears (such as Bartlett), pistachios and persimmons.
How much to thin depends upon the tree species. With peaches and nectarines, it's important to make room on the branches for each fruit to grow to 2-1/2 to 3 inches in diameter. Thin by pulling off 3/4 to 1-inch long fruit in April and May, leaving one fruit every 6 inches. This results in more fruit on the ground than on the tree, but it's important to produce large, flavorful fruit and to minimize limb breakage.
While it's best to thin early in the season, it is never too late to do some thinning where trees are having difficulty sizing the crop. Removing small fruit from overloaded trees, even shortly before harvest, will pay off in larger average fruit sizes.
Grape varieties such as Thompson seedless may also benefit from fruit thinning. Removing entire clusters after the berries have set helps to enlarge the berries on the remaining clusters. Remove undersized or misshapen clusters first.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
- Author: Ed Perry
Home gardeners often become concerned when their fruit trees begin dropping fruit prematurely. In some cases, fruit drop is nature's way of reducing a heavy fruit load. In other cases, premature fruit drop may be caused by pests and diseases, adverse weather conditions or poor cultural practices.
Apples may have a couple of periods when fruit drop occurs. The first is often after the flower petals fall off and may last two to three weeks. The very small dropping fruits are the ones that were not pollinated, so will not develop further. Many fruit species need to be pollinated by bees. Lack of pollination may be the result of cold or wet weather during the bloom period, or by a lack of honey bees. Also, if there is freezing weather just before the flower buds open, more fruit drop may occur.
Other adverse weather conditions may also contribute to fruit drop. For example, persimmons may drop if the weather turns suddenly hot in spring, just as the small fruits begin to develop. Trees not receiving adequate irrigation water would be more prone to dropping fruit.
Pests and diseases may contribute to the problem of premature fruit drop. Cool wet weather during the bloom period of walnuts often results in infections of walnut blight, a bacterial disease that damages catkins, leaves, and newly-pollinated nuts. Infected nuts may drop prematurely. Premature ripening and fruit drop often occurs in apples and pears that are infested with codling moth larvae.
In apples and pears, a second drop occurs once the fruits are about the size of marbles, usually in May or June. This is commonly referred to as “June drop.” Fruit drop at this time of year is thought to occur as a result of competition between fruits for available resources.
Some fruit tree species, such as plums, may experience a mid-summer fruit drop. Proper fruit thinning can help to prevent this. How much to thin depends upon the tree species. With peaches and nectarines, it's important to make room on the branches for each fruit to grow to 2 ½ to 3 inches in diameter. Thin by pulling off ¾ to 1-inch long fruit in April and May, leaving one fruit every 6 inches. This results in more fruit on the ground than on the tree, but it's important to produce large, flavorful fruit and to minimize limb breakage.
Thin apricots when the fruit is about ¾ inch in diameter, leaving 1 apricot every 3 inches. Thin plums when the fruit is ¾-inch-long, leaving 1 plum every 4 to 6 inches. Thin apples after the usual May or June drop. Leave 1 apple every 6 inches or allow only 1 apple to remain per spur. Asian pears should be thinned to leave only 1 fruit per spur.
When mature fruit begins to drop, it's a sign that the fruit is ready for harvest.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County.