by Sammy Stein

Created on: December 08, 2008

We rotate crops for good reasons and doing this in a small garden is very important.

Certain diseases like certain crops and each crop group has its own pests and diseases which have evolved to fare particularly well if that crop group is planted there. For example club root likes brassicas, phytophthera and potato cyst eelworm like potatoes and mosaic virus likes tomatoes and cucumbers. Growing the same crop year after year in the same space means the populations of these pests will increase to uncontrollable levels. By rotating the crops you remove the host plants from each area and the population of the diseases or pests reduces to manageable levels.

Crop rotation also helps maintain fertility. Different groups of plants use nutrients at different rates. Brassicas need heavy doses of nitrogen for leafy growth, onions require potassium, root crops need phosphorous and so on. By rotating crops you ensure the balance of nutrients in the soil remains good. For example, legumes have root nodules in which live colonies of bacteria which fix and trap nitrogen from the air. By growing legumes and then following them with a crop of brassicas you ensure the brassicas use the nitrogen fixed into the soil by the previous legume crop. This means you need to fertilise the ground less and you can ensure the cycle of nutrients is maintained.

As well as the crops themselves, there are certain host plants which are ornamentals and these need to be considered too. For example, brassicas are susceptible to club root and this is also carried by tagetes and other ornamental plants in the garden so as well as rotating the crops, it helps to remove these secondary host plants in order to reduce the populations of the disease organisms.

Crop rotation also helps with weed control. For instance, onions compete porly with weeds and you can lose an entire crop if you plant them in an area prone to weed infestation but growing potatoes the year before will mean weeds are far less of a problem in that site because potatoes are great weed surpressors as their leafy foliage spreads over the ground, reducing light and therefore weed seed germination so following a potato crop with onions helps reduce the need to weed the second crop.

Crop rotation is a good idea whatever crops you grow. There are some crops which do not fit into the crop rotation system and these are the perennials like rhubarb and fruit trees but if you rotate crops around them, you will reduce the build up of potential pests and diseases too.

Crop rotation is part of the IPM (Integrated Pest Management) programme) which is a programme which uses natural means like crop roatation, companion plants and naturally based chemicals to keep a balanced fertility and pest control system in place in you garden and this really suits small gardens well.

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