Broccoli, Cauliflower, Cabbage, Kale, Swede and Brussels Sprouts are all members of the 'brassica' tribe of vegetables, and many of them enjoy similar growing conditions. As such, this section will have a general outline for brassica growing followed by specific requirements, planting times etc. for each species.
GERMINATION and PLANTING: Brassica seedlings are best started off in trays, punnets or home made newspaper pots. Sow seeds in seed mix about 5mm under the surface. Keep constantly moist until leaves emerge, then water regularly with a gentle spray. They are ready to transplant to the garden when they're 8-15cm tall. They should be spaced about 30cm apart for the smaller varieties and 50cm apart for larger varieties. Closer spacings will result in smaller heads but more of them, and wider spacing the reverse.
ENVIRONMENT: Plenty of sun and shelter from winds, espcially southerlies.
SOIL: A firm and well manured soil, that has had an application of lime a couple of weeks prior to planting if the pH of your soil is below 6.5 (A simple pH testing kit, with driving instructions, can be purchased from any good garden shop for less than $20). Brassicas are heavy feeders so the manure / compost addition is important. The soil should also be well drained. Boggy soils will likely cause problems with root diseases.
WATER and FERTILISER: Water regularly, especially when young. As with many veggies, a mulch layer around the plants and between the rows, such as straw or dried grass clippings, will help to hold the moisture in the soil for longer. Brassicas can be fertilised regularly through their growth cycle with liquid organic fertilisers such as comfrey tea, manure tea, liquid seaweed, and so on.
PESTS AND DISEASE: Take note that brassicas are quite vulnerable to both aphids and white cabbage butterfly. The white butterflies lay eggs which turn into green caterpillars that will munch on your plants. Aphids appear as grey or green clusters around the growing tips of the plants. Caterpillars can be plucked off by hand, if you can spot them. Aphids can be blasted off with a stream of water from the hose. However the best way to manage these pests is to ensure that there is a good level of biodiversity in the garden, with companion plants such as phacelia and marigolds to attract beneficial insects which kill aphids and caterpillars.
HARVEST and USE: For broccoli and cauliflower, the heads are best harvested when they are still tight. You may notice a head beginning to expand and become less dense. In a matter of days it can completely spread out and begin turning to flower heads. So if you see a head begin to do this, even if the head is not the size you might have hoped for, harvest it and cook up a nice meal. Cabbage and brussels sprouts are best harvested when the leaves are tightly bundled still. A slight doming or unfurling at the centre of a cabbage or brussel sprout is an indication that the flower head is on its way - harvest as soon as possible. Kale leaves can be harvested as required until the plant goes to flower.
Broccoli: Sow seeds September through to February.
Brussel Sprouts: Sow seeds from September to November.
Cabbage: Sow seed August through to January.
Cauliflower: Sow seeds September through to January.
Kale: Sow seeds in early spring (Aug-Oct) or summer (Jan-March). Kale thrives in cooler temperatures.
Kohl Rabi: Sow seeds September through to January
Swedes: Sow seeds September through to January
SEED SAVING: Brassicas are notoriously difficult to save seed from. In the end, it's not actually that difficult, you just need to take care to avoid cross pollination. Keep in mind that cabbage, broccoli, cauliflower and brussels sprouts are all the same species! You can imagine what a cabbage x broccoli might turn out like - not too useful!
As with any seed saving, we want to choose the best plants to save seed from. This might be a large, tight head, or frost hardiness, whatever qualities you're wanting to select for. Since brassicas produce side shoots which will make flowers and seed pods, you can actually still harvest the main head and still use the plant for seed production.
When I'm saving brassica seeds, I like to select the best 10 plants from a crop of at least 20. To free up space in my garden beds, I carefully dig up the plants and move them to a more 'wild' area of my garden, where I clear the turf with a grubber and prepare the ground for planting. The plants can then be planted in fairly close proximity which will further ensure good pollination.
The group of plants may need some support as the seed heads grow very tall. String can be strung between four stakes, placed at the corners of the stand of plants, to provide enough support to keep the seed heads upright until mature.
Seed heads are ready for harvest when they are plump and starting to dry out. Do not water the plants while the seed heads are maturing, dryness is good. When the seed pods are mature, harvest the whole plants and hang them upside down somewhere dry for the final maturation / drying stage of the seed pods. You can then get the seeds out by rubbing the pods between your hands.