Stop harvesting from one plant entirely. It will send up a central stem, branch, and produce small yellow flowers. This takes two to three weeks from the decision to the first flowers.

Watch the seed heads?

After flowering, each head develops a dandelion-like pappus — a fluffy parachute. The seed is ripe when the fluff begins to show and the head starts to open.

Bag before they shatter?

This is the step people skip. Tie a paper bag or a fine mesh bag over the head while it is still tight, then check daily. When the head has opened inside the bag, cut the whole stem and shake the seed into the bag.

Spread the seed on paper in a dry room for a week. Rub gently to separate the seed from the fluff, then winnow by pouring between two bowls in a light breeze.

Ten seeds on damp paper in a warm place for seven to ten days. Seven or more germinating means the lot is good. Store in a sealed jar with silica in the fridge.

Saved seed from this crop?

Germination rates, what came true and what crossed — post it and let other growers learn from it.

Annual, biennial and vegetative crops all save differently. The index compares them side by side.

Growing brassica — 79 varieties, spacing and isolation

Varieties79 in the catalogue

Seed type34 heirloom, 44 hybrid, 1 open-pollinated

Days to harvest20–220 days

Germination3–7 days

Spacing0.1–0.61 m (4–24 in)

Soil pH6.0–6.0

Life cycleBiennial (oleracea) / often annual (rapa)

PollinationInsect-pollinated

Seed life4–5 years

Where to go next

Growing brassicaFull cultivation guide — sowing, feeding, pH, harvest.All 79 varietiesSortable comparison table with days to harvest and spacing.Saving brassica seedLife cycle, isolation, seed life and the step-by-step protocol.Isolation calculatorEvery crop, both units, with a verdict for your plot size.Download the dataCSV and JSON of all 891 varieties, CC BY 4.0.What goes wrongSeedlings, bolting, no germination, root problems.

At a glance

Fastest to harvestArugula 'Rocket'20-40 days

Longest seasonPurple Sprouting Broccoli 'Early Purple Sprouting'220-240 days

Can you isolate brassica?

Your plot, in metres and feet

Enter the longest side of the space you have. Two plantings go at opposite ends.

Longest side

Shortest side

Units