Gardening > Crop Rotation

Crop Rotation

Potato Flowers

Potato Flowers
© Rainer

Growing the same crops in the same place year on year risks the depletion of the soil and the build up of pests and diseases in the soil. Different crops have different mineral requirements and eventually if one type of vegetable is grown on one spot season after season the demand for those particular minerals will become too great and the crops will fail in the soil which can no longer meet its needs. When crops are continually grown in the same place there is also the risk that whatever pest or disease they suffer from will become endemic. There is however something of a catch 22 situation in repeat sowing in that as the soil becomes more depleted by the specific demands of the crop so the crop becomes less healthy and more prone to disease and attack by pests.

The best way to avoid these problems is to practice crop rotation. This involves dividing the vegetable patch into four sections and only planting vegetables from a similar group (e.g. brassicas) in one of three sections in any one year. The fourth section is reserved for non-annual vegetables which do not like being moved such as seas kale, asparagus and rhubarb. The three rotation plots should be prepared every year and the groups of crops sown in the next plot from the one they occupied during the first year. This way it will take two years for any one group to return to its original plot.

The three groups can be divided into Roots (beetroot, potatoes, parsnips, salsify, scorzonera), Brassicas (broccoli, Brussels sprouts, kohl rabi, radish) and Others (aubergine, beans, celeriac, leeks, lettuces, onions, tomatoes).

In the first year, a few weeks before planting and sowing, plot one of the four should be double dug incorporating plenty of well-rotted manure and adding two handfuls blood, fish and bone meal per square yard. This plot can then be planted up or sown with root crops. Plot two should be prepared by single digging and the same application of blood, fish and bone meal and then sown with the Others group of vegetables. Plot 3 should be prepared in the same way as plot 2 and then planted up with brassicas. In the second year the group of vegetables grown in plot 1 should be moved to plot 2, plot 2 to plot 3 and plot 3 to plot 1.

Obviously this plan has to be tempered by the space available. For example it may be necessary to grow a tall crop (like runner beans) in one particular spot every year because, if moved, they would block light from other vegetables. It may also be necessary to grow some permanent crops in borders if there is not enough space for a plot 4. Crops like tomatoes, chard and sweetcorn can do very well in borders even next to flowers and small trees and doing this can free up more room in the vegetable plot. If you really can't face the thought of setting up a three year rotation, a reasonable compromise would be root crops one year then above the ground crops the next. However it must be borne in mind that if a crop does badly one year it should never be followed by one from the same family in the next year (i.e. swede is a root crop but also a brassica).