Many apple trees naturally tend to flower and bear fruit heavily one year and very little the next, a trait referred to as biennial or alternate bearing. A heavy crop one year inhibits flower development the following year. Regular flowering and bearing is potentially achieved by hand-thinning small fruit within two to four weeks of bloom, or spraying trees with a hormone thinning spray shortly after petal drop during the heavily flowering years.
Lack of Pollination
If an apple tree blooms well but fruit fails to develop, insufficient pollination is likely responsible. Most apple varieties are self-unfruitful, with sterile pollen, or partially self-fruitful, with only some viable pollen. So for most apple trees to successfully produce fruit, multiple varieties of apple trees with overlapping periods of bloom must be planted within 100 feet of each other. Bees are primarily responsible for transferring pollen between trees, so disruptions of bee activity -- such as broad-spectrum, persistent pesticide use, rain or wind -- during the bloom period will reduce pollination and limit fruit development.
Improper Care or Site Problems
Apple trees require ample sunlight to bear fruit and will suffer if grown in the shade. Competition for light, moisture and nutrients from other plants grown near the apple can also impact fruiting. Pest infestations, diseases and poor nutrition or insufficient moisture that have an impact on overall tree vigor also negatively affect bearing. Additionally, choosing an apple cultivar well suited to the amount of chilling hours that a site receives is important for blossoming and fruit development.
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