How to thin fruit trees
Thinning is the process of reducing the number of fruitlets on the tree so that the remaining fruit reaches good size and quality. It also helps prevent broken branches in some heavy-cropping varieties. Thinning helps guarantee a crop next year, by discouraging biennial bearing – the tendency to crop heavily one year and only lightly the following year. The amount of thinning that you have to do depends on many factors, such as variety, and the fruit set. The latter is in turn caused by weather conditions and the success of pollination.
Sometimes, the tree itself makes the decision, and abandons many of the fruitlets, which end up dropping off the tree. In some years this can be very intense, and you may be surprised to see a carpet of fruitlets on the ground under the tree. For example, in 2013 weather in the UK was very different to normal particularly in spring. Usually a tree starts growing at the end of May, but in that year, the cold conditions and cold soil meant that the tree didn’t get the incentive to start growing until the second week of June. So the tree started producing loads of new shoots. New shoots need energy, just like the fruit which was also developing. This reduces the energy available for seed growth. When the seeds do not develop properly, the tree abandons the fruit around it, and it drops.
This tendency to self-thinning by dropping excess fruit is known as June drop, though the exact time that it occurs depends on the variety and its blossom period.
Different varieties have different thinning characteristics. James Grieve has a perfect, automatic thinning. No manual thinning is required.
Climate effects on thinning
Spring frosts can have a dramatic effect on fruit set and therefore on whether thinning is necessary and to what degree. The effect of spring frost damage is not always visible straight after the event. In apples, after frost damage, the usual June drop occurs earlier: instead of taking place in late June, the fruitlet drop will start in early June and will be completed by the end of June. The tree provides an indication of what is going to happen: the fruitlets that are going to drop have a dull appearance, and those that are going to stay are shiny, and grow rapidly in size.
Triploid varieties are highly sensitive to spring frost damage. If you have both diploid and triploid trees, it is a good idea to start thinning the diploid varieties first, and in particular, those that produce smaller fruit at picking time.
Another factor to take into consideration is that the blossom on 2 and 3-year-old wood always opens earlier than flowers on 1-year-old wood. So when you are thinning, not only are you regulating the amount of fruit that the tree will produce this year, but you are also affecting next year’s crop. So it is a good idea to complete thinning only later in the season, after the tree’s natural June drop has been completed, and when you have a good picture of the number of viable fruitlets on the tree.
How to thin apples by hand
You can start to thin early apple varieties in late May, when the fruitlets are still small – under an inch in diameter. Use a narrow-tipped cutter to remove some of the fruitlets so that they are better spaced. Leave the best-sized fruitlets. Cut just underneath the fruitlet, leaving the stalk. Always cut out the central fruitlet in a group, because this is the king fruit and it is misshapen. Typically you may find groups with as many as 12 fruitlets. These can be reduced to about 5, which are still too many, but it is still early in the season, so it’s a good idea to thin the fruitlets down to this degree at the present time, late May. In July you can take another look at the tree and reduce the number of fruits down to 2 per group. Three apples per group are too many in any variety. When thinning, save the largest, healthiest fruitlets, and those that have the best exposure to light and air.
Watch a video on how to thin apples of early varieties.
How to thin pear trees
Pear trees generally do not need thinning, but in the case of a heavy fruit set, you can thin as per apples. Manual thinning of pear trees should be performed only when the fruit has begun showing a drooping tendency, so in late June-early July. Thin with a narrow-tipped cutter, leaving the stalk on the tree. Remove any small, misshapen or injured fruit, and then work on the clusters of fruit. Doubles can be reduced to singles, and in each group, two is enough. Ensure that fruit is spaced at about 4-6 inches apart.
How to thin plum trees
Plum trees and greengages are liable to overcropping, and so thinning helps to protect the tree from damage as well as achieving good fruit size. It also helps prevent the tendency to biennial bearing. You can start thinning out plums in late May-early June, if the set of fruit on plum trees is strong. Use a narrow-tipped cutter, leaving the stalk on the tree. Start by removing any plums that are damaged, or smaller than the others. Then remove some plums so that the ones left are a couple of inches apart. Where there are two together, cut them down to one. When plums overcrop, the branches break, and the fruit is not as good.
Watch a video on thinning the Golden Gage greengage.
How to thin apricots, peaches and nectarines
Apricot, nectarine and peach trees are subject to setting heavy crops and so they should be thinned to avoid damage to trees. They should be thinned using a cutter, so that the fruits are about 4 inches apart. Clusters of fruit will have to be thinned accordingly.
How to thin cherry trees
Usually, thinning is not necessary for cherry trees. If you think that there is too much fruit on the tree – particularly if the tree is stressed by weather conditions or disease – you can thin the fruit from April to mid-May. Reduce the groups to about 10 cherries per spur.