Crop Rotation
Crop rotation is a system where different vegetable crops are grown in the same space in sequence; either in consecutive years or within one season. For example, a cool-season crop (such as lettuce) may be grown in the spring, followed by a warm-season crop (such as tomatoes) in the summer.
Crop rotation avoids a decrease in soil fertility, as growing the same crop repeatedly in the same place will eventually deplete the soil of various nutrients. This may be prevented by following a crop that leaches the soil of one kind of nutrient with a crop that returns that nutrient to the soil. For example, legumes, such as peas and beans, have nodules on their roots which contain nitrogen-fixing bacteria and make it available for the next crop. It therefore makes good sense to alternate them with plants such as leafy brassicas or potatoes that are nitrogen-hungry.
Crop rotation is also used to control pests and diseases that can become established in the soil over time. As families of plants tend to be attacked by similar pests and diseases, regularly changing the planting location can break or limit the pest cycles. This is particularly useful for in organic gardening, where pest control is achieved without synthetic pesticides, herbicides and fungicides. For example, clubroot, which attacks brassicas and potato eelworm (nematodes) may be alleviated by rotation.
Rotation Groups
The majority of vegetables can be broken down into the four following rotation groups:
| Legumes & Pod Crops Broad beans Dolichos beans French beans Okra Peas Runner beans |
Alliums Bulb onions Garlic Leeks Shallots Spring onions Welsh onions |
| Brassicas Brussels sprouts Cabbages Calabrese Cauliflowers Kales Kohl rabi Oriental mustards Purple sprouting broccoli Radishes Swedes Turnips |
Solanaceous, Root & Tuberous Crops Aubergines Beetroot Carrots Celeriac Celery Cocoyams Parsnips Potatoes Sweet peppers Sweet potatoes Tomatoes |
The vegetable plot should be divided up into four sections, each one filled with plants from one particular rotation group. The next year they should all be moved on into the next section as shown in the diagram below. In this way, each group will return to its original section every four years.
However, several vegetables, including perennials and many salad plants, do not fall into a major rotation group. As salad plants stay in the ground for a relatively short time, they are useful for filling temporary gaps in vegetable beds or for intercropping. However, you should ensure that they are not grown in the same patch of soil year after year. Perennials should be grown in a permanent bed at one end of the plot, and should not be rotated.