Anyone who had success with a first-time vegetable patch last year should now be prepared for crop rotation this season. Many vegetables don't like being grown in the same place two years running because the nutrients they need from the soil have been so depleted.

Crop rotation prevents a build-up of pests and diseases in the soil, such as clubroot in brassicas, eelworms in potatoes and tomatoes and root rots in peas and beans.

Some crops, such as potatoes and squashes, can suppress weeds, minimising problems for following crops. Crop rotation also helps soil fertility, as different crops have different soil requirements and benefits. Changing crops from year to year minimises deficiencies and allows the soil to replenish. Alternating between deep-rooted and fibrous-rooted crops also improves soil structure.

As each vegetable group is prone to the same disease and attracts the same pests, it makes sense to rotate them each year. Groups should be moved around in sequence so they don't return to the same spot for at least three years.

Divide your vegetables for rotating into groups - potatoes, legumes, brassicas and roots. The potato family includes potatoes, aubergine, peppers, tomatoes and chilli. Roots include carrots, parsnips, celery and celeriac, Florence fennel and parsley; brassicas include Brussels sprouts, broccoli, cabbage, cauliflower, kale, pak choi, rocket, cabbage, swede, turnip and kohlrabi, while legumes consist of the pea and bean family.

Different crops have different nutrient requirements. If you have four areas, two should be given manure or compost each year, while the other two should be limed to make them alkaline. In alternate years each plot should receive the other treatment to help to keep the soil pH balanced.

In the first year, grow potatoes on the manured ground, in the second year, the same patch should be suitable for roots which prefer a light soil on the alkaline side, so you may need to add lime if the pH is low.

In year three, manure the plot again and move the legumes there. Peas and beans take nitrogen out of the air and store it in their roots, which are left in the soil after harvest. The nitrogen will suit the brassicas well, which should be put in, in year four.

Of course, you can add other vegetable families to your four plots. Plant beets and onions with your roots, as they don't need rich soil. Put cucumbers into rich soil with the legumes. Lettuces can slot in almost anywhere, while rhubarb, sorrel and artichokes are perennial so they will need a permanent position. Fruiting vegetables, the squash family and salads can be fitted in with any of the groups.

Some mixed cropping in the vegetable garden can prove unfruitful if you plant from different families within the same bed. For example, don't plant asparagus with beetroot, cabbage with onions or tomatoes with fennel.

Other vegetable neighbours which seem to make good companions include leeks and carrots, marrows and green beans and peas and sweetcorn.