Does your apple or pear tree crop heavily one year and then produce little or nothing the next? This is not uncommon. It’s known as biennial bearing. Some cultivars have a natural tendency to this condition, such as the Blenheim Orange and Bramley’s Seedling, but weather conditions and soil fertility can also contribute to the problem.
The causes of biennial bearing are not well understood.
The flowers that produce the following year’s crop begin to develop when the current year’s fruit is forming. If the tree is producing a heavy crop, its energy will be focussed on developing the fruit and not next year’s flowers. This, in turn, can lead to a much smaller crop the following year. Without a crop to support, the tree’s energies are directed to flower production and so the cycle continues.
In some cases, it’s possible that this pattern of alternate cropping is triggered by external factors i.e. the tree did not receive sufficient moisture or nutrients, or frosts and rain interfered with the fruit set. The tree produces a poor crop as a result, which stimulates the tree to produce excessive flowers the following year.
Once a tree is in a pattern of biennial bearing it can be difficult to break the habit. One strategy is to control how much fruit the tree produces. Thinning fruit buds [see Identifying fruit buds and growth buds] is considered by some to be more effective than thinning the fruit. This is done by rubbing off some of the fruit buds, leaving two or three per spur. The theory is that the tree will produce a moderate crop which will leave it with the resources to produce blossom for the following season. However, this does not always cure the problem.
It may be easier just to accept that your apple tree only produces fruit every other year, and learn to enjoy the bumper crop when it arrives. However, in years when there is a heavy yield, it is still advisable to remove some of the developing fruit to avoid the weight of the crop causing damage to the branches.