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Gardening in Washington State

Why Didn’t My Onions form Big Bulbs?

Onions form bulbs in response to day length or the number of hours of daylight. There are two main types of onions: those grown in northern latitudes that bulb in response to long days, and those grown in southern latitudes that bulb in response to short days. The long-day onions grown in Washington will start to bulb when there are 14 hours of daylight. If they are not planted early enough in the spring, bulbing will begin before the plant grows enough to produce a large bulb. When purchasing onion seed, Washington gardeners should be sure to select only long-day onion cultivars.

onion

Big and small onion bulbs

This material is excerpted from the WSU publication Growing Onions in Home Gardens FS097E.

Submitted by: Marianne Ophardt, August 31, 2015

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