Brassica

What counts as a brassica?

Brassicas are members of the cabbage family (Brassicaceae). It's a big group, and once you know the shape of the leaves you'll start spotting the family resemblance. The main ones a UK grower meets are:

• Cabbage — including red, savoy and pointed types
• Kale — one of the easiest and hardiest crops you can grow
• Broccoli and calabrese — the purple-sprouting and green-headed kinds
• Cauliflower — fussier, but rewarding
• Brussels sprouts — the classic winter crop
• Turnips, swede, kohlrabi and pak choi — plus rocket and radish, which are brassicas too

Why they're grouped together

The reason brassicas get lumped into one bunch is crop rotation — the practice of moving crop families to a different bed each year. They belong together because they share the same problems and the same appetites.

They're hit by the same pests and diseases: cabbage white caterpillars that strip the leaves in summer, flea beetle, cabbage root fly, and above all clubroot — a soil-borne disease that swells and distorts the roots and can linger in the ground for years. Grouping brassicas means you can move the whole family on together and avoid building these problems up in one spot.

They're also hungry, thirsty feeders. Brassicas want rich, firm soil that's been well manured for a previous crop, and they prefer it on the limey side — a slightly alkaline soil helps keep clubroot at bay. They like to be planted firmly; loose soil gives wobbly, disappointing plants.

Following legumes in rotation

Here's the neat bit. In a rotation, brassicas traditionally follow legumes — peas and beans. Legumes pull nitrogen from the air and leave it behind in the soil through their roots. Brassicas, being leafy and greedy for nitrogen, make excellent use of that leftover fertility. Pea bed one year, cabbages the next.

If you'd rather not dig your beds over each season, brassicas sit happily in a no-dig system too — a yearly layer of compost on top keeps them fed, and the firm, undug soil actually suits them.

Growing notes for the UK

Brassicas love the British climate — cool, damp summers and mild winters are exactly their thing. Sow from spring into early summer depending on the type, and start most under cover or in a seedbed before transplanting to their final firm spot.

The single biggest job is protection. Cover plants with fine insect netting from late spring to keep cabbage white butterflies off, and protect young plants from pigeons, which adore them. Watch out for slugs on small transplants too.

Many brassicas are at their best in the cold half of the year: kale, sprouts and purple-sprouting broccoli all stand through winter, and a frost sweetens their flavour. That makes the family one of the most useful things you can grow for filling the hungry gap when little else is cropping.