Apple trees do not reliably produce a harvest every year; this irregularity is common in fruit production. The expectation of an annual crop is often interrupted by a natural cycle where a very heavy yield is followed by a year with little to no fruit. This fluctuation is a significant challenge for both commercial growers and home orchardists. The tree’s natural resource management drives this inconsistency, creating an alternating pattern of abundance and scarcity.
Understanding Biennial Bearing
This pattern of irregular cropping is formally known as biennial bearing, or alternate bearing. It describes a tree that yields a large crop one year, the “on-year,” and a significantly reduced or absent crop the next, the “off-year.” The difference in yield between these two years can be extreme. This cycle is a resource allocation mechanism that serves as a survival strategy for the tree.
During the heavy production year, the tree expends nearly all its energy developing fruit. The following year, the tree must recover its strength and vegetative growth, leaving minimal resources for reproduction. While almost any apple tree can fall into this pattern, certain varieties, such as ‘Honeycrisp’ or ‘Bramley’s Seedling,’ are genetically more prone to biennial bearing. This rhythm is undesirable for cultivation, leading to inconsistent supply and smaller, lower-quality fruit during the heavy cropping year.
Internal Factors Driving Production Cycles
The primary biological driver of this alternating pattern is the physiological trade-off between developing the current season’s fruit and initiating the flower buds for the next season. Flower bud initiation, the process where vegetative buds convert into reproductive buds, occurs during the summer before the fruit is set. A heavy crop year coincides with this critical period for next year’s flower formation.
Developing seeds within the current season’s fruit produce high levels of plant hormones, specifically gibberellins, which are translocated to the nearby buds. These gibberellins act as an inhibitory signal, preventing the vegetative buds from transforming into flower buds for the following spring. Since the buds are inhibited during the heavy crop year, the tree has very few flowers the next season, leading to the “off-year.”
Additionally, the immense energy demand of a heavy fruit load can deplete the tree’s stored non-structural carbohydrates. These stored sugars and starches are needed to fuel the growth of new flower buds and support the early stages of fruit development the following spring. The competition for these energy reserves, combined with the hormonal inhibition from the seeds, creates a physiological barrier to consistent annual production. The tree is unable to simultaneously ripen a large crop and prepare for a large crop the next year.
Strategies for Promoting Annual Yield
To break the cycle of biennial bearing, growers must intentionally reduce the crop load during the “on-year” to ensure resources are redirected toward future flower bud formation. The most effective management practice for promoting consistent annual production is fruit thinning, which involves the early removal of excess young fruitlets.
Thinning must be completed early in the season, ideally within the first month after bloom, before the developing seeds release the inhibiting gibberellin hormones. Removing the fruitlets early drastically reduces the total number of seeds, thereby removing the hormonal signal that prevents next year’s flower bud initiation. This action also conserves the tree’s carbohydrate energy, allowing it to be stored for the following season’s bloom and growth.
Pruning also plays a supportive role by maintaining a balanced tree structure and promoting light penetration, which is necessary for healthy fruiting wood. By removing older, less vigorous wood, pruning helps ensure the tree can support a moderate, consistent crop rather than an overwhelming one. Selecting varieties less prone to alternate bearing can help, but managing the crop load through early, timely thinning remains the most direct way to stabilize the tree’s annual yield.