The Importance of Fruit Thinning

By Amy Grundling 

Fruit trees set more fruit than what they can structurally support or properly develop. This occur more often in trees that was not pruned during the previous season.  The excessive fruit remain small due to increased competition for carbohydrates and other nutrients. This increased demand for carbohydrates weakens the tree, which makes it more susceptible to pests, diseases and water stress. Excessive fruit in one season can also cause the tree to have alternate bearing or limb breakage. Thinning the fruit is therefore necessary to prevent these problems.

Fruit thinning is the removal of certain flowers and fruitletts after fruit and natural dropping have occurred. The benefits of thinning immature fruits include:

1. The remaining fruit receive more carbohydrates and therefore develop into bigger fruits.
2. The fruits receive more sunlight which improves the fruit colour and flavour.
3. The chance for limb breakage decreases due to the lighter load of fruits.
4. The spread of disease decreases. For example, fruits that are close to each other can spread brown rot from one to another.

 
Thinning Methods
There are two main thinning methods that are used, which include hand- and pole-thinning. Hand thinning is slower than pole thinning, but more accurate. Hand-thinning is when some fruits are removed to ensure the remaining fruits do not touch each other at maturity. Therefore, on short spurs only 2 to 3 fruits can be left. On long branches fruits that are double, small, disfigured and damaged fruits should be removed. Pole-thinning involves using a pole due to the size of the tree which is too large for hand-thinning. A cloth is attached to the tuber hose at the end of the pole, to decrease bruising of fruits and branches.

​The amount of fruits that should be thinned depends on the species and the individual tree’s fruit load. Stone fruits such as apricots and plums are small, therefore they should be thinned 5 cm to 10 cm apart from the branch. Nectarines and peaches are larger fruit, therefore they should be thinned 7.5 cm to 12.5 cm. Unlike stone fruits, which produce one fruit per bud, pome fruits produce cluster fruits on one bud. Therefore, pome fruits need to be thinned so that one fruit per bud are available to develop. The overall rule is that for every 15 cm of branch there should be one fruit.

Thinning should be done at the correct time of season depending on the type of specie. The method and amount of fruit thinning is also determined by the species of the tree. Thinning is an important management practice in the fruit industry to develop a constant fruit yield every year of high quality.