Saving Seeds from Onions and Leeks

Various varieties of onions (Allium cepa) are widely grown in home gardens. They, and related species such as leeks (Allium ampeloprasum), are usually grown as annuals for consumption in the year they are sown, but in fact, they are biennials. Biennials have a two year life cycle, with growth of roots (bulbs), stems and leaves in the first season and after a cold period, production of flowers, fruits and seeds in the second year. Thus seed saving this crop is a two year project!

In our regular monthly seed saving presentation, Cathy Christie reviewed the “how to” of saving seeds from these biennial species.

Saving Onion Seeds

As has been discussed previously, seed saving starts with open pollinated (OP) seeds, which will grow “true” to the parent plant. To save your own onion seeds, use fresh seeds rather than onion sets. This will result in stronger, healthier seedlings and will ensure biodiversity is maintained.

Onion Seedlings. Image credit:

To begin, start your onions from seed indoors and then transplant in spring, spacing to allow for bulb formation (about 15 cm depending on type being grown). Cathy recommends starting with about 150 plants, of which half will be harvested for seed. While 20-50 plants is sufficient for seed saving, at least 80 plants are needed to maintain genetic diversity.

Onion harvest. Image credit: Anna Sadura Healey

Once about half the tops have fallen over, knock down the rest and then wait a few days to dig up the bulbs to be cured. Chose an area outside protected from sun and rain, or inside in a well ventilated space.  Discard or eat any less than perfect bulbs, as you want the healthiest and most vigorous for propagation.

Drying onions. Image Credit: Anna Sadura Healey

In the second year, re-plant the bulbs as soon as possible and then wait for the scapes (leafless flower stalks) to emerge.  Hundreds of white flowers arranged in a spherical umbrel will appear and be pollinated by various insects. Each small capsule will eventually dry and split open, revealing three tiny black seeds.  To harvest these, just cut the scapes once the seed capsules have begun to split and allow them to dry further. 

Onion Seeds. Image credit:

Isolation Distance

In the second year, when flowers appear, different onion varieties must be separated from each other by a distance of at least 800 feet (244 metres) to ensure they do not cross pollinate. This can be a challenge in a city garden, but where it is not possible to maintain this distance, a physical barrier such as floating row covers can be used.

Growing Leeks for Seed

Leek seeds can be saved in a similar manner to onions, although they may not need to be dug up over winter. Many, but not all, varieties can winter in the ground and will produce flowers the following year. As with onions, the flowers will appear on long stalks, and when dry tiny black seeds can be harvested by threshing. Leeks are insect pollinated and like onions, require an isolation distance of 800 feet or more in the season in which they flower (second season).

Kingston Area Seed System Initiative leeks. Image credit Anna Sadura Healey

Seed Viability

Both onion and leek seeds are viable for a relatively short time, generally about two years if stored in a cool and dry environment. 


Lee Buttala and Shanyn Siegel, eds. The Seed Garden; The Art and Practice of Seed Saving. Decorah IA, Seed Savers Exchange Inc., 2015.

Seed Savers Exchange

Seeds of Diversity Canada