How Onions Grow

by National Gardening Association Editors

There are more than 300 widely scattered species of onions in the world, and the bulb onion we grow is just one of them. The onion is a biennial plant, which means that it grows one year and produces its seeds the second. Between these two seasons onions have a dormant phase, which helps us gardeners.

Onion's Growth Cycle

The first-year onion plants begin their growth by putting out green top leaves during the cool weather. They store a lot of energy in those leaves. When the weather gets warmer and the days longer, the plants stop putting out new top leaves. Instead, they take the energy from the leaves and store it in the expanding bottom bulbs. Eventually the leaves fall over and shrivel up and the plants appear dormant. Inside the bulbs, however, the plants are storing the energy to put out flowering seed stalks when they start growing again. That's the goal of any plant - to produce the seed to keep its species going.

Onion bulbs are best for eating, cooking and storing before they've started to put their energy into making seed. That's why gardeners harvest onions after just one season and pick off any seed pods as soon as they appear.



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