Fruit thinning for homeowners is one of the most difficult jobs to do when producing tree fruit. With all the expense and hard work that has gone into producing a healthy productive tree, the last thing homeowners want to hear is that they should knock the majority of the young fruit on the ground. However there are a couple of important reasons why fruit crops should be thinned. The most important reason to thin fruit is to increase fruit size. Another significant reason to thin fruit is to reduce over bearing that often leads to a heavy crop in one year and almost no crop in the second year. A third reason to thin fruit is to reduce limb breakage that occurs when too much fruit is left and the fruit begins to size.
Most deciduous fruit trees benefit from fruit thinning. Apples, pears, Asian pears, apricots, plums, peaches, kiwi, and persimmons all respond positively to fruit thinning. Cherries and nut trees are usually not thinned. Why do these fruits benefit from thinning? Because thinning balances the amount of fruit left on trees with the leaf surface that provides the energy to grow and ripen fruit. Leaving too much fruit on a tree creates a burden for the tree and takes energy from other processes occurring at the time of fruit development. One of those processes is fruit bud development for the coming crop. When too much fruit is left on a tree, fruit bud production for next year will be limited, causing the tree to have a light crop next year. Also, when too many fruit are left on a tree the competition between fruit for scarce nutrients will limit the size of each individual fruit.
Learning how much fruit to thin off your tree will take some practice. Each fruit type will require a little different method. When working with apples, Asian pears, and European pears, thin fruit to one per spur. The spur is the short woody structure where flowers arise. You should leave only one fruit for about every six inches of branch. If your tree is healthy and vigorous it will have more than one spur every six inches along a branch. So you will need to leave some spurs with no fruit on them. This helps to balance your crop for next year. When choosing which fruit to leave look for the largest fruit. Fruit that is small or damaged should be dropped first. Homeowners should thin fruit as early as possible. Thin before each apple reaches the size of a dime in diameter. This usually occurs within the first 20 days after petal fall. Removing these small fruit early will keep energy available for the fruit that remain and fruit buds for next year. Thinning by homeowners is typically done by hand. Be careful not to break off the spurs while thinning. Spurs will produce flowers and fruit for many years if not broken during thinning and harvesting.
When working with apricots, peaches, nectarines, and plums you will notice fruit is borne mostly on one year wood and does not come off a spur. Plums will be borne on both one year wood and small spur like structures. When thinning these trees try to space young fruit along the branches as singles with about six to eight inches between fruit. Young fruit should be thinned off trees within 30 days of the end of bloom. Be advised that peaches, nectarines, cherries and plums will have a natural drop that occurs near early June. This is referred to as June drop. This is the trees way of lightening the crop load. You may want to leave a little heavier crop than the final crop to see which fruit the tree intends to drop for you. And, with time you will learn how to adjust for the June drop. Some peach growers use sticks or lengths of plastic pipe to knock branches to speed up thinning. If you have just a few trees I would recommend staying with hand thinning. It will be more accurate at leaving the proper amount of fruit per branch. As the fruit matures and branches begin to bow from the weight you may need to take more fruit off each limb to protect your tree from limb breakage, especially when the tree is young. If you do not want to thin more fruit from the tree limbs you may need to use poles or props to hold up the limbs.
Remember when raising dwarf fruit trees to thin a little extra fruit off after bloom because the tree is not as strong structurally as a semi dwarf or standard tree. Dwarf fruit trees are precocious and tend to bloom and set heavier fruit crops at an early age. Protect their young branches from being overloaded in the first few years.
It is my feeling that a good pruning job helps to maintain a healthy tree by removing wood that contributes to over fruiting. Pruning is the first stage of fruit thinning. Without proper pruning fruit thinning is not a feasible practice.