There are several reasons why an apple tree might be dropping fruit before they become ripe. Most of the time, it is natural for apples to fall from the tree, but the time of year and the size of fruit will give us a hint as to what is actually happening behind the scenes.
Apple trees can drop fruit from poor pollination, to reduce a heavy fruit set, from lack of nutrients or water, from summer pruning, or from pest damage. Read below to determine what exactly is affecting your apple tree.
Cold and rainy weather can prevent honeybees and other insects from pollinating apple blossoms. If you notice small apples falling off your apple tree at the beginning of the spring after the petals have fallen off the apple blossoms, this can indicate the blossom was not properly pollinated, and the tree will start dropping any blossoms that did not get pollinated.
Apple blossoms are also susceptible to freezing temperatures and can fall off after a cold snap in your area. Once the flowers start to bud, freezing temperatures would kill off the flower buds and the apple tree will naturally shed the blossoms and small apples it started producing.
An apple tree will produce many more flower blossoms than it can possible grow into mature apples, knowing that not all the blossoms will get pollinated. A normal pollination rate of 5-10% would result in a ‘full’ crop of apples, so don’t worry if some young apples start dropping once they reach 1/2 inch to 1 inch in diameter. If your apples start falling at this time, it’s natural, and referred to as the ‘June drop’.
The ‘June drop’ happens between mid-June and mid-July and it is a way for the apple tree to prune itself from over pollination that would result in a heavy fruit set that the branches or the roots would not be able to support. The apple tree produces a hormone that will limit the number of apples it can produce. Instead of producing a large number of stunted apples, it concentrates its energy on fewer fruit so that these apples may grow to their fullest potential.
Apple trees produce clusters of 4-8 apple blossoms. You can help out the apple trees natural culling by manually pruning off all but the best apple in each ‘cluster’ once they grow to about 1 inch in diameter. Using sharp scissors, cut the stem of the smallest, diseased, or mis-formed apples in each cluster, leaving the largest and healthiest to grow to maturity. Each apple should be no less than 4-6 inches apart, so prune any that are too close together. Apples grown too close together can actually ‘push’ each other off as they grow.
Pruning young apples from your apple tree will also prevent the apple tree from becoming a biennial. When an apple tree produces too many apples one year, it will skip a year to rest and restock its carbohydrate reserves before producing another bumper crop in the following year. Proper apple pruning will prevent this, and allow the apple tree to produce a consistent crop of apples every year.
Pruning out extra apples will also help the overall health of the apple tree in the long run, by preventing stress from forcing it to produce too many apples at once.
Another reason why semi-mature apples can fall off an apple tree is from heavy summer pruning. Apple trees should be pruned in the winter or early spring while the tree is still dormant. Read our in-depth guide on how to prune apple trees to fully understand what happens when you over-prune. Pruning an apple tree in the peak of summer will cause problems like a lack of carbohydrates from too many leaves being removed, especially younger and more functional leaves. The reduction in photosynthesis will cause a shortage of carbohydrates which is needs to produce healthy apples. Apples will drop if the leaf to fruit ratio falls below 20:1 – that is 20 leaves for every 1 apple on the tree.
A carbohydrate shortage can also occur naturally through environmental conditions like cloudy weather or low temperatures, which reduces the rate of photosynthesis, thus producing less carbohydrates. High nighttime temperates can also lower carbohydrate reserves as the apple tree respiration rate increases.
As apples grow larger and begin to ripen, they produce ethylene, a hydrocarbon gas which is a ripening hormone that triggers a few changes in the apples. It softens the texture of the apple, intensifies the flavour, and changes the colour of the skin.
Ethylene also triggers the production of enzymes that break down complex sugars and help loosen the stem from the branch to help free the apple from the tree when you go to pick it. As the complex sugars start to break down and the abscission is formed, the apple looses strength and is only connected by small vascular strands, which can easily be broken by wind, animals, or simply the weight of the apple itself. This is called ‘pre-harvest’ drop.
Some varieties, such as McIntosh, are very prone to pre-harvest fruit drop. Ripening of the fruit and loosening of the stem is an irreversible process. Once the stem loosens, there is no way to strengthen it back up.
If your apples fall off the tree before they are ripe year after year, there are growth regulators that can be sprayed on to the tree before the fruit starts to ripen that will slow the ripening process and the loosening of the stem. These growth regulators should be applied between 7 days and 4 weeks before the peak ethylene production or harvest date – depending on the apple variety. These growth regulators are mostly used in commercial orchards to extend the growing season, or increase the size of the apples.
Fun Fact: An extra week on the tree can add 1/4 inch in size to the apple.
Water and Nutrition
Another reason why apples drop pre-maturely is water and nutrition levels in the soil. Low magnesium, high potassium, and high boron can all contribute to early dropping of apples.
The type of soil will also play a role as to when the apples will ripen and drop. Sandy soils will drop apples before apple trees planted in heavier clay soils. Read our guide on the best soil types for apple trees to learn more about their effect and growing conditions.
Lack of water can also contribute to apples falling off the tree from drought related stress. The apple tree will begin dropping as many apples as it thinks it needs to in order to survive, and for the remaining apples to fully mature. Be sure to water your apple tree deeply once a week, especially while the flowers blossom, and as the apples start to mature.
Pests on both the apples and leaves of your apple tree can cause the apple to fall off the tree pre-maturely.
A high number of leaf eating insects can affect the photosynthesis of the leaves, which reduces the carbohydrates it can produce, which it needs in order to produce apples.
Apple maggots are one of the most common pests affecting apple trees. The apple maggot fly will lay eggs just under the skin of the apple. Once the eggs hatch, they feed on the flesh of the apple. This causes the pulp to break down and rot and the apple falls to the ground.
The plum curculio are small beetles measuring 1/4 inch long. The female adults will cut a 1/8 inch crescent shaped hole through the skin of the apple and hollow out a small cavity where she will lay eggs. About 5 days later once the larvae hatch they will burrow into the fruit. The flesh will start to rot, and the apple will fall to the ground.
The codling moth is the most serious pest for apples, who lay eggs at night on the leaves and fruit of the apple tree. As the larvae emerge, they tunnel their way through to feed on the flesh and seeds of the apple. As they mature, they push frass out the entry hole. You can identify codling moth damage by finding entry holes surrounded by darker skin.
All of these pests can cause damage to apples, and cause them to fall off the tree pre-maturely.
By now you should be able to identify what is causing your tree to drop apples pre-maturely, whether it be pests, or natural culling, and give you a better understanding of the growth cycle of apples.
How many apples should be left on a tree? In the first few years, it is best to pull off all the flower blossoms to prevent the tree from producing any fruit, in order to use that energy to create a strong root system. Read our guide on apple tree roots to understand how a healthy root system can affect fruit production.
After the first few years, the apples should be pruned to be no less than 4-6 inches apart for maximum growth.