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Onion bolting: What can the gardener do when onions flower?

Gardeners growing onions may in one season or another find their onions have bolted and wonder what to do for the crop.

This bolting occurs when an onion stalk begins to flower at the top, according to the article “Onions” by Texas AgriLife Extension Service of Texas A&M University.

“Flowering of onions can be caused by several things, usually temperature fluctuation,” as explained in the article.

Because “an onion is classed as a biennial, it usually takes two years to go from seed to seed,” according to Texas AgriLife Extension Service. But onions can bolt, meaning the plant has been tricked into developing seed due to extreme weather where temperatures change from cold to warm and back again in a short period of time, the article explains.

When this type of weather occurs, the onion goes from a dormant state during cold temperatures to a growing state when the weather warms up. And just as it resumes growing, the onion experiences cold weather again, making it return to the dormant state. As a result, “the onion bulbs prematurely flower or bolt,” according to the article.


Though some gardeners cut the flower off the top of the onion stalk, they won’t prevent the bolting.

“The onion bulbs still will be edible but probably will be smaller,” the article explains.

To offset losses, gardeners might want to use the bolted onion as soon as possible since bolted onions with the flower stalk growing through the middle make storage difficult, according to the Extension Service.

An onion plant with a bloom at the top indicates bolting, which can be caused by extreme temperature fluctuations.
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