Saving brassica seed
The hardest family to save from, because most are biennial and must survive a winter before they flower. But one plant gives thousands of seed, and the method is genuinely satisfying.
- Life cycle
- Biennial (oleracea) / often annual (rapa)
- Pollination
- Insect-pollinated
- Isolation
- 800 m–1.6 km, or time separation
- Seed life
- 4–5 years
- Yield
- 1 plant gives 1,000+ seed
Brassicas are the group that teaches you why seed saving is a skill rather than a chore. Brassica oleracea — cabbage, kale, broccoli, cauliflower, kohlrabi — is biennial. You grow the plant in year one, it survives the winter as a stump, and in spring it sends up a two-metre spike of yellow flowers.
Brassica rapa — pak choi, mizuna, tatsoi, turnip — is faster and often sets seed in the same season, because it bolts so willingly.
The protocol
- 1
Select the best plant, not the first
Mark your healthiest, truest-to-type plant during the growing season. Do not save from a weak one.
- 2
Overwinter it
For oleracea: lift the stump with roots intact, trim the outer leaves, and heel it into a sheltered bed or a large pot in a frost-free but cold place. It needs cold to trigger flowering, but not to freeze solid.
- 3
Let it flower in spring
A tall spike with yellow four-petalled flowers. It will flower for three weeks and is covered in bees.
- 4
Bag or separate in time
This is where most people lose the crop. Bag the flowering head in fine mesh and hand-pollinate with a brush, or grow only one variety per species that year.
- 5
Harvest the pods
Seed is in long thin pods that turn from green to brown. Pick as they brown, before they split — brassica pods shatter readily.
- 6
Dry and shell
A week in paper bags, then crush the pods and winnow.
What goes wrong
Assuming distance will save you. The honest figure for brassicas is 800 m to a mile. In a garden that is not achievable, so use time (stagger flowering) or bags.
Winter kill. Most kale and cabbage take −8 °C, but not sitting in waterlogged ground. Lift and heel them in somewhere sheltered.
Crossing within the species. Kale and Brussels sprouts are the same species and will cross. So will pak choi and mizuna.
Shattering pods. Check daily once the pods start to brown.
Saved seed from this crop?
Germination rates, what came true and what crossed — post it and let other growers learn from it.
All 14 protocols
Annual, biennial and vegetative crops all save differently. The index compares them side by side.