Biennial bearing facts for kids

Biennial bearing, also called alternate bearing, is when a fruit tree produces a lot of fruit one year, and then very little fruit the next year. Imagine your favorite apple tree giving you tons of apples this year, but hardly any next year! This is what biennial bearing means.

In the "on" year, the tree makes too much fruit. This can lead to small fruits because there isn't enough energy for all of them to grow big. Sometimes, the branches can even break because they are carrying too much weight! After such a busy year, the tree doesn't have enough energy to make many flowers for the next year. So, the next year becomes an "off" year, with very little fruit.

Scientists think this happens because of special plant chemicals called plant hormones, especially one called gibberellin. When there's a lot of fruit, these hormones are produced in the tiny seeds inside the fruit. They might tell the tree to slow down on making new flowers. Also, making so much fruit uses up all the tree's stored energy, like its food reserves.

Which Trees Do This?

Biennial bearing is common in some fruit trees. These include mango trees, apple trees, pear trees, apricot trees, and avocado trees. You almost never see this problem in grape vines, though!

It's also a big deal for Arabica coffee plants, especially in places like Ethiopia and other parts of East Africa. A year with a huge coffee harvest is often followed by a year with a very small harvest. This can happen even if the weather is perfect for growing coffee. Sometimes, the difference between an "on" year and an "off" year can be huge, with ten times more coffee in a good year!

Why Does It Happen?

This up-and-down pattern happens because of how the plant uses its energy. In a busy "on" year, the coffee plant puts almost all its energy into making coffee beans. It doesn't have much left for growing new stems, shoots, or flower buds. So, in the "off" year, the plant needs to catch up on its own growth. It focuses on growing bigger and stronger, instead of making flowers and fruit.

How to Help Trees

Luckily, farmers and gardeners can do things to reduce or even stop biennial bearing. Here are some ways:

• Pruning: This means carefully cutting off some branches. It helps the tree focus its energy better.
• Thinning: This involves removing some flowers or very young fruits early in the season. It helps the tree not make too much fruit in the "on" year, so it has energy left for the next year.
• Fertilizer and Water: Giving the tree the right amount of food (fertilizer) and water helps it stay strong and healthy, even after a big harvest.
• Special Trees: Using certain types of trees, called cultivars, that are known to produce fruit more evenly each year can also help.

See also

In Spanish: Contrañada para niños