A number of pests and diseases can affect brassicas, and they’re often easier to prevent than cure. Crop rotation, good soil preparation and care of the plants will lessen the likelihood of many problems. Crop rotation reduces the build-up of soil-borne diseases and disorders; brassicas shouldn’t be grown in the same position within two years. In the rotation cycle, brassicas normally follow beans and onions, which allows plenty of time for autumn preparation of the brassica bed. The brassicas also benefit from the extra nitrogen peas and beans add to the soil.

Avoid acid soil, which promotes the fungal disease clubroot. Liming the soil, providing good drainage, for instance, by using raised beds, and using plants raised in 15cm (6in) pots can allow fairly good crops to be grown even if clubroot is present.

The best defence against the three main brassica pests – caterpillars, the cabbage root fly and pigeons, is enclosing the plants in a cage covered by insect-proof netting. This is best put in place on planting, before insect pests begin to lay their eggs, or pigeons can peck at, or uproot, the seedlings.

To prevent cabbage root fly, place a 7.5cm (3in) disc or collar of roofing felt or carpet underlay around the base of the stem when planting out to prevent it laying its eggs. Growing garlic or chives nearby is said to throw them off the scent. Discourage slugs and snails with a biological control such as Nemaslug, or use other non-biological controls, such beer traps or a barrier of crushed eggshells.

Brassicas need good amounts of space between the individual plants to allow air to circulate around them, which helps to prevent diseases from taking hold. For the same reason, it is also important to remove weeds and any old, withered foliage as they appear.

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