What To Do When Onions Bolt

Growing onions is so satisfying. However, you may not know what to do when onions bolt. Seeing flower stalks forming on your growing onions can be disheartening.

A bulb on the top center stalk of your onion means it has begun the process of flowering and making seeds. This is called “bolting,” which is terrible news for onion growers.

What Is Bolting?

Bolting is the term that describes when a vegetable plant starts to seed or flower before it should. When onions bolt, the bulb part of the onion stops growing and will not mature further. The energy that would make the onion bulb is now directed towards making the flower stalk. 

Onions and shallots are biennial crops, which means that they grow the first year and flower the second year. When an onion or shallot forms a flower in the first year, it is called bolting.

Why Do Onions Bolt?

An onion bolts in response to stress. Stress can happen in several ways: too hot, too cold, not enough water, or too much water. Temperature fluctuations can also cause onions to bolt.

Swings in temperature may cause the onion to think it is in the second year of growth when it is supposed to flower.

For example, warm temperatures followed by cool weather can encourage onions to go dormant. Once warm temperatures return, the onion may believe it is beginning its second growing season and produce seeds. Leeks bolt under stress the same way onions do. What makes leeks bolt walks you through it.

The onion reacts to the stress by putting its energy into reproducing and making seeds. If you would like more information about how to grow onions, read this blogpost.

What Should I Do When My Onions Bolt?

• Harvest and use (or preserve, see preserving tips below). 
• Cut off the flower on top, or cut the entire bolting stem, so the onion stops producing seeds. (This won’t restart bulb growth.) You can leave the onion in the ground for a few weeks. The onion won’t continue bulbing or get any larger, but it will “keep” in the ground and can be used later. 

• Do not wait to harvest until the onion leaves turn brown and fall over (as you do with onions that don’t bolt). Bolted onions may rot or become fibrous if left in the ground too long.
• Leave a couple of bolting onions to flower until they produce seeds. Save the seeds to plant next season.
• Use onions in my favorite garden salsa recipe to add body and balance to the flavor.

How Do I Preserve Bolted Onions?

Use bolted onions right away, just as you would other onions. Bolted onions will not store well, and you need to preserve them differently than onions that did not bolt.  

Here are a few ideas for ways to preserve bolted onions: 

• Chop and freeze.

• Cut up the onions and dehydrate them. Use dehydrated onions whole, or process them into onion powder. Store the dehydrated onions whole for the most robust flavor, and then blend small amounts for powder. 

• Slice onions and freeze dry them. (This is my FAVORITE way to preserve onions.) Freeze-dried onions can be stored and used “as is” or processed into a powder. Looking for more information about freeze-drying? Read this post, Freeze Drying Tips for Beginners.