Vegetables belonging to the same family tend to be affected by the same pests and diseases, which can build up to damaging proportions if the same crops are grown in the same piece of ground for several years. Therefore, it makes sense to rotate the various families around the vegetable plot each year.
Rotation is difficult to achieve in small plots
However, it is very difficult to maintain a strict rotation in a small garden because of the different sized areas for each crop. There may be several crops of a particular vegetable, for example cabbage, in a single year and this adds to the difficulty of finding a ‘new’ site each time.
Besides, tools and boots are efficient spreaders of pests and diseases, and certain weeds often provide a ‘bridge’ for harmful organisms when suitable crop plants are not available. Because of the wide variety of crops grown and the restrictions of space in a small garden, only short rotations are possible and these are of limited value.
Even so, it is worth trying to avoid following a crop with another of the same family. Rotation offers the opportunity to add organic material and lime to the soil in such a way as to be an advantage to particular crops.
Organic material is very beneficial for potatoes, celery, courgettes and sweet corn, while it tends to make Cabbage family plants too leafy. So, it should be applied before potatoes, etc., and the Cabbage family should be kept away for a while.
Applying organic material before potatoes, each year in a four-year rotation, means that a different quarter of the vegetable area gets it every year and the entire site will be covered by the fourth year. If slugs in potatoes have been a problem, apply the organic matter before the Pea and Onion families instead.
If the soil is acid, and lime is to be applied, apply it before the Cabbage family and keep it away from the Potato family. It prevents clubroot disease of the Cabbage family but encourages potato scab disease. If lime is applied before the Cabbage family, in a four-year rotation, then the whole vegetable area will be covered in four years, which is about right on an acid soil.