Seed Saving Guide – The Onions

Most people are familiar with the common garden onion, with its large, multi-layered bulb, that makes a person’s eyes water, when it is cut.

There are three basic groups of onions, within the Cepa species, and only one of them produces seed. A second group produces topsetting bulbils, and the third comprises those onions that divide vegetatively, such as shallots and potato onions.

1. Cepa group: Biennial onions that produce flowers and seed. This group includes our common garden onions. (Check out The Ultimate Guide to Growing Onions)
2. Proliferum group: produces topsetting bulbils. Besides the bulbils, these types of onions can occasionally produce flowers, which can cross with the cepa group. The onions of this group are known as Egyptian onions, tree onions, or walking onions. (Growing Guide for the Proliferum Group)
3. Aggregatum group: reproduces similarly to garlic – by ‘cloves’. This group includes shallots, potato onions, and multiplier onions. (Growing Guide for the Aggregatum Group)

Common onions are biennials, requiring two growing seasons to produce more seed. As for all biennials, it is best to dig the bulbs in the fall, roguing off-type bulbs (which can be eaten) and only keeping the bulbs that are true-to-type for planting in the spring. This is called the seed-to-bulb-to-seed method.

In mild winter areas, a gardener can plant onion seed in late summer, and leave the bulbs in the ground to overwinter, and the onions will produce flowers for seed saving the following spring. This is called the seed-to-seed method. It is less reliable at producing true-to-type seed, since off-type bulbs are not rogued out.

(For more details on growing onions, click here.)

The onion greens will begin to bend over toward the end of summer or in early fall. When you see this happening, you know it’s almost time to harvest the bulbs. The bulbs need to be dried (or ‘cured’) for 10 to 14 days, in a warm area out of the sun.

Many garden books tell you to just pull them and dry them in place in the garden, but if they get sunburned, they won’t store as long and they’ll rot more easily. Either remove them to a warm, dry area where they won’t be exposed to sunlight, or, if you do choose to leave them in the garden, you can spread a light layer of dry grass clippings over the top of them. They’ll still be able to dry out properly without the threat of being sunburned.

After the onions are dry, you can braid the onions as you would garlic, or remove the dried tops, before storage.

It is best to store them between 33℉ to 45℉, with humidity less than 70%. They can store this way for up to 6 months.

After a sufficient cool, resting period, (during which the onion will not sprout or grow, no matter how optimal the conditions you give it) the onion will enter dormancy. Once the onion is in dormancy, when the conditions are right the onion will break dormancy, sprout, and begin growing again.

Re-plant the best onions the following spring. They will soon send up a flower stalk with hundreds of little flowers in a globe shape.

These flowers will set seed better if insects are allowed to do the pollination work as they naturally do. If you have more than one onion flowering in your garden at the same time, either alternate day caging or try bagging with hand-pollination.

Harvest the seed heads when they begin to turn brown, but before they shatter. Bend the stalks and place the seed head inside a brown paper bag before cutting the stem, to avoid losing seed.

Allow the seed heads to continue to dry on a tarp in a warm, dry location out of the sun. Most of the seeds will fall from the seed heads quite easily once the individual pods are fully dry. To remove the rest, you can gently flail the seed heads, jog on them, or rub them with your hands.

To winnow, use a gently-blowing fan rather than wind so that the air flow is kept consistent.

Shallots, Potato Onions, and Multiplier Onions are propagated vegetatively. That is, they don’t produce flowers and seed. Instead, they produce underground bulbs, very similar to garlic cloves.

When harvesting shallots or multiplier onions, save the smaller ones for replanting. These bulbs are naturally identical to the mother plant.

Top-setting Onions

Egyptian onions, or walking onions, also reproduce vegetatively, though instead of growing many separate cloves underground, they grow bulbils at the top of a stem.

Occasionally these onions will produce flowers, which can cross with common onions. When this happens, the flower stalks should be bent over to prevent them reaching maturity. Do not break them off, or water could collect in the hollow leaves and cause rotting.

Harvest the bulbils when the stems begin to wilt. You can either eat them (use them fresh or store them in the freezer) or you can replant them to propagate Egyptian onions.

Plant the bulbils in the fall, throughout the United States. You can harvest them as onion greens, or bunching onions, in the spring.

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