What is crop rotation?
Put simply, it is growing specific groups of vegetables on a different part of the allotment each year.
Why is it important?
Rotating the crops helps reduce a build-up of crop-specific pests and diseases plus, since different crops take different nutrients from the soil, you are avoiding the risk of particular soil deficiencies. Some crops even put back nutrients into the soil that are helpful to other crop varieties. So crop rotation helps balance the nutrients in the soil.
Do all crops need rotating?
Short answer – No. Perennial vegetables (such as rhubarb and asparagus) are fine to leave where they are each year. Certain annual crops such courgettes, pumpkins, squashes, marrows and cucumbers can be grown where convenient. So too French and runner beans, sweetcorn and lettuces. (But it is still best to avoid growing each too often in the same place).
How do you go about rotation?
Whilst we will give examples in later posts on this site, the principles are simple. There are five main groups of vegetables:
1. Legumes: Peas and broad beans (French and runner beans suffer from fewer soil problems and, as explained earlier, don’t need rotation)
2. Brassicas: Brussels sprouts, cabbage, cauliflower, kale, kohl-rabi, oriental greens, radish, swede and turnips
3. Onions: Onion, garlic, shallots, leeks
4. Potato Family: Potatoes and tomatoes
5. Root vegetables: Parsnips, carrots, beetroot, celeriac, celery and fennel (NOTE: swedes and turnips are brassicas)

So, to run a 4-year rotation, divide out four roughly equal-sized plots (A,B,C,D) and then choose your rotation plan. e.g.

So potatoes are grown in Plot A in year 1, in Plot B in year 2. Plot C in year 3 and Plot D in year 4. Onions and Root Vegetables are grown in plot B in year 1, in Plot C in year 2 and so on…

Effective rotation will help keep your plants nourished, healthy and free from pests.