If crops are grown in the same place every year there is a risk that soil borne pests will increase and that plants will lose their vigor. It is best to have a system of rotating crops so that particular nutrients required by a specific are not used up and pests do not have a chance to multiply.The most basic crop rotation system is to split vegetables into 4 families: potato, root, legume, brassica. Using a 4 courses system means that each type of crop is only grown in the same place every 4 years.
It is not always easy to get a good rotation going as different crops need different amounts of space. In small gardens it is questionable whether rotations work as roots from different crops can spread into adjoining beds. The pragmatic approach is to try to rotate crops if possible and to avoid growing the same crop in the same place year after year.
The diagram and table below give basic information for a 4 course rotation. There are other rotations and the scheme can be modified to suit individual requirements.
|A||Early potatoes, potatoes, tomatoes|
|B||Carrots, beetroot, parsnips, spinach, chard, lettuce|
|C||Overwintered onions*, garlic*, leeks*
followed by peas and beans.
|D||Summer cabbage, winter brassicas, spring cabbage, other brasicas|
|A||Grazing rye or phacelia (Cover crops or green manures)|
|B||Autumn planted onions, leeks, garlic, leeks, green manure|
|C||Winter tares (Green manure)|
|* = planted in the previous year|