Why your fruit tree has ‘on’ and ‘off’ years – and what you can do about it

Have you ever noticed that your backyard apple or pear tree produces a large quantity of fruit one year, but a disappointingly small crop the next? This common occurrence is known as alternate bearing or biennial bearing. It is a natural tendency in many fruit trees, where a season of heavy fruit production (an On-Year) is followed by a season of extremely light or even no yield (an Off-Year), and vice versa.

This can be frustrating if you are hoping for a consistent supply of fresh fruit. Beyond the inconsistent yield, a heavy On-Year can actually damage the tree, breaking limbs from the weight of the fruit itself, and often results in smaller, lower-quality fruit. Understanding why your tree does this can help you manage it for better, more reliable harvests.

What causes this fluctuating fruit production?

Environmental factors

Adverse weather conditions can trigger this alternate bearing cycle. For example, a late frost during the crucial flowering period or unusually high temperatures during the fruit set can damage or kill the developing flowers and young fruits. Extended periods of cool, rainy, or hot, dry weather during bloom can reduce pollinator activity, leading to poor pollination and a light crop. If your tree loses its flowers early in the season from these conditions, it will likely end up being an Off-Year. On the other hand, if conditions are ideal an excessive amount of fruit can lead to an On-Year that sets the next season up for an Off-Year.

Fruit trees naturally drop fruit throughout the spring and early summer. This first drop occurs shortly after the petals fall, when the fruit is about the size of a pea. This can be caused by poor pollination, or because bad weather limited pollinator activity. The second drop, often called June drop, happens in early June when fruit is about ½ to 1 inch in diameter. This is a natural thinning process, where the tree sheds excess fruits due to competition for limited resources such as water and nutrients.

Biological factors

The leading theory behind alternate bearing is energy management. The flower buds that will produce next year’s crops begin forming while this year’s fruit is still developing. If there is a heavy crop this season, most of its energy (sugars) is diverted to maturing that fruit, leaving little available energy for creating new flower buds for the following spring.

Once the alternating bearing starts, it can become a self-perpetuating cycle due to hormonal changes within the tree. A heavy crop can suppress the growth of new vegetative shoots during the summer and fall, and these shoots are where the next year’s flowers form.

Some fruit trees varieties are simply more prone to alternate bearing than others due to their genetic makeup. For instance, apple cultivars like ‘Elstar’ are highly susceptible, while ‘Braeburn apples tend to bear more regularly. If you are planting a new fruit tree, research the bearing habits of different cultivars and the rootstock (if available) to help you select a more consistent producer.

What can you do?

Understanding the causes of alternate bearing is the first step. The most effective strategy to manage alternate bearing and promote consistent, high-quality fruit production is thinning. Although your tree naturally thins some fruit June drop, additional hand thinning is often necessary.

Hand thinning involves manually removing excess fruit from the branches and offers several benefits:

• Allows the remaining fruit to grow larger and develop better quality
• Reduces the energy demand on the tree, allowing it to put more resources into developing flower buds for the next year’s crop
• Minimizes limb breakage caused by overloaded branches

For apples, hand thinning should ideally be done within about six weeks of full bloom, but if that time has already passed now, thinning now is still better than not thinning at all. Try to leave the largest, healthiest apple in each cluster and space remaining fruit about 8 to 10 inches apart along the branch. Pears, plums and apricots also benefit from hand thinning, but these fruits can be spaced about 6 to 8 inches apart.

By actively managing your fruit trees though thinning and being aware of the environmental and biological factors at play, you can encourage more consistent production and enjoy a better harvest year after year.