Brassicas: Broccoli, Cabbage, Kale & More
Advanced seed saving from biennial crops that cross readily within species.
Overview
Brassica seed saving is challenging because most are biennials (requiring two seasons) and they cross freely within species. All cabbages, broccoli, cauliflower, Brussels sprouts, kale, and kohlrabi are the SAME species and will cross! Plan carefully.
Crops Covered:
insect-pollinated
dry processing
2-3 weeks after harvest
4-5 years (often longer)
Understanding Pollination
Brassicas are insect-pollinated and cross readily. All common brassicas are Brassica oleracea and will cross with each other.
Isolation Distance
1/2 mile or more (or grow under insect netting)
Key Tips:
- ALL are same species: cabbage, broccoli, Brussels sprouts, kale, kohlrabi, cauliflower
- Grow only ONE variety for seed each year
- Can cage plants with insect screen and introduce flies
- Wild mustard and canola will also cross with brassicas
- Isolation by caging is most practical for home gardeners
Step-by-Step Guide
Brassicas are biennials - select best plants in fall to overwinter.
- Choose healthiest, most typical plants in first year
- Select 6+ plants to maintain genetic diversity
- Overwinter in ground (mild climates) or root cellar
- Kale is hardiest; cabbage needs protection
- In spring, replant stored roots or let overwintered plants grow
In second year, plants bolt and produce yellow flowers.
- Plants will send up flower stalks in spring
- Yellow flowers are typical of brassica family
- Bees are primary pollinators
- Cage with screen and add flies if isolating
- Flowering period lasts several weeks
Harvest when pods are dry but before they shatter.
- Pods (siliques) form after flowers fade
- Turn from green to tan/brown when mature
- Seeds rattle inside dry pods
- Harvest before pods shatter and drop seeds
- Cut whole stalks and dry further on tarps
Break pods to release seeds and winnow clean.
- Place stalks in bag or on tarp
- Crush pods by walking on them or hitting with stick
- Winnow in breeze to remove chaff
- Screen to remove large debris
- Seeds are small and round
Harvest Timing
| Crop | Harvest Stage | Days After Flowering |
|---|---|---|
| Kale/Collards | Pods tan and dry, seeds brown | 30-40 days |
| Broccoli | Pods dry, seeds hard | 30-40 days |
| Cabbage | Pods papery, seeds brown | 30-45 days |
| Brussels Sprouts | Pods dry | 35-45 days |
Processing: Dry Method
Let pods dry on plant or cut and dry on tarps. Thresh to release seeds.
- 1Cut stalks when most pods are dry
- 2Hang or lay on tarp to finish drying
- 3Thresh by walking on pods or hitting in bag
- 4Winnow in breeze
- 5Screen out large chaff
Drying & Storage
2-3 weeks after harvest
Dry, warm location with good airflow
Test for Dryness: Seeds hard and don't dent when pressed with fingernail
Glass jars, Paper envelopes
Cool, dark, dry. Excellent long-term storage.
4-5 years (often longer)
- Very long-lived seeds when properly stored
- Test germination if seeds are old
- Small seeds - easy to store in small containers