Pollination: Brassicas are insect pollinated and cross within species only (see chart above ).

Isolation: Seed to Seed says you must have 1 mile between flowering cultivars of the same species, but I’ve found the distance can be far less, depending on hills, valleys and what is inbetween. Too hard you think – then become member of the Koanga Institute or your local seedsaving organisation and help us to do it. It will certainly always be a very big challenge to keep this seed strong.

Minimum Numbers:  If you want to grow your own seed that has the strength to remain a strong  cultivar over time, you must plant a minimum of 300 plants, rogue out the 100 least true to type, and save the seed from the rest. This kind of grow out needs to be done on a regular basis every few years to keep the seed alive, however on its own it is not rigorous enough to keep the seed line strong.
To keep the seed line strong for the long haul you must dig out the 6-10 best examples of your brassica at the ready-to-eat stage (from a grow out of 300) and plant them far away from each other, so that they can not be cross pollinated (maybe 2 km apart). This means they will self pollinate. After you have saved the seed from these plants the next step is to grow 50 plants from each of these 6 separate plants all together in one place. There will be lots of variation in these plants as any weaknesses will be amplified. When they get to the eating stage chose the ten best plants. It is unlikely that many home gardeners will be able to do this as it is a long and costly exercise. Traditionally villages held only 1 brassica line each, and it would have been a cultivar developed over time in that place that probably also had lots of variation unlike the cultivars we know today. If we are going to keep our various more modern cultivars alive we must  engage in the rigorous selection process described above.

When To Plant: The following members of this family are best planted in early spring to harvest a good seed crop in the following Summer. broccoli, cauliflower, mustard. The rest of this family will produce a far stronger seed crop, and you have a chance to rogue out the bolters if you plant them in the Autumn and over winter them, to save seed the following summer. cabbages are tricky in that they must actually be fully mature before the solstice if you want them to head to seed in Spring/ Summer.

Rogueing: Remove and eat any which are not true to type.

Support /Protection: brassicas will grow very tall when they go to seed. We use different methods for keeping them up off the ground for different crops. Sometimes it is good to put a strong stake in the round by individual plants and tie them to it, sometimes best if they grow through a grid and others we put stakes in the ground around the outside of the bed and strong string around that so they stay above the bed.
The hardest part of growing brassica seed is often keeping the birds off it until it is mature enough to harvest. . I would recommend being prepared to cover the ripening seed, as the birds seem to regard brassica seed as their favourite food, just as the bees regard the flowers as theirs!
We always cover the seed heads with bird netting, so often make the support structure tall enough to hold up the bird netting when it’s needed.

Harvest: Take a large sheet out to the garden and place it right beside your seed crop, then use sissors or a garden shark to cut the stems just below the seed heads and place them on the sheet. Brassica seed pods often break open when they are harvested so be sure to harvest just before they are totally ready, or do the job very carefully.

Drying: Place the sheet in the greenhouse until all heads/pods are crunchy dry,

Threshing: Once we have our dry seed pods we then throw them into our half barrels (cut off length wise) and dance on the pods, or put them onto a tarp on the ground and dance on them there. The seed all falls out very easily and can be winnowed to clean it.

Winnowing: Brassica seed can be easily winnowed in the breeze or in front of a fan and it can also easily be separated from the chaff using seedscreens.

Seed Life Expectancy: When stored in cool, dry, dark conditions, cabbage seed will remain viable for 4 years, broccoli and cauliflower 5 years, kale and collards 4 years, Chinese cabbage and Chinese mustard 5 years, turnip 5 years, radish 5 years.