How to Harvest Onion Seeds

With some plants, it’s obvious how to save seeds. Others? Not so much.

Onions certainly fall into that “not so obvious” category.

Thankfully, once you know where and how the seed is produced on an onion plant, you can easily seed save it!

Harvesting Onion Seeds

Onions seeds are only produced after the onion has bolted—aka when it has produced a flower stalk.

This means that if you want to produce your own onion seed you’ll need to leave a few onions in the ground until warmer weather hits, which will trigger the bolting process.

To harvest the onion seeds, wait until the seed heads are sufficiently dry on the plant. The flower heads—where the seeds are located—will appear dry, brown, papery.

Separating Onion Seed From the Chaff

To separate the seeds, rub the dried flower pods against a rough surface to separate the seed from the dried flower covering. A wire mesh strainer works well for this. Be careful not to press down too hard and crush the seed.

Next, use airflow to further separate the seed from the chaff. One way to do this is to slowly pour the seeds into a bowl, and use a fan (or wait for a windy day) to create airflow. 

As you pour the seed over a bowl, gently shake it back and forth. Repeat this process three to four times until you have 80-90% clean seeds.

It’s hard to adequately explain this process in words, so be sure to check out the video tutorial above.

Finally, pick out any remaining chunks of debris by hand.

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Storing Your Onion Seeds

Store the seeds in an old pill bottle or other small container and label them accordingly. Store in a cool, dry place out of direct sunlight.

When stored properly, onion seeds can remain viable for up to 5 years. I like to err on the side of caution and only save about two year’s worth of seed after each harvest.

Happy gardening!