What is Crop Rotation?

Crop Rotation

It is not a good idea to grow the same type of vegetables in the same area of ground each year. As this can cause a build up of soil-borne pests and diseases, which attack those specific crops. The problem can be avoided to a certain extent using a planting method called 'crop rotation', which involves growing similar crops together on designated parts of the vegetable plot each year. In addition, as each type of vegetable has specific nutrient and soil requirements, it also makes sense to group similar types together. Thus making it easier to give them the exact soil conditions and nutrients they require.

How Does Crop Rotation Work?

The crop rotation method is mainly used to avoid soil nutrient loss and the unnecessary spread of disease. This is achieved by dividing the vegetable plot into three or four separate areas, and growing groups of similar vegetables together in each area. In following years, these vegetable groups are then grown in a different area, and subsequently rotated around the plot. Usually over a three or four year cycle.

This system does not work for all vegetable types, especially long term crops such as fruit bushes, rhubarb and asparagus, which need to be established in the same area. A separate strip of land at one end (or corner) of the plot is often allocated for such permanent crops.

What are the Vegetable Groups?

Vegetables can be divided into four basic groups:

Legumes: peas, mangetout, beans, dwarf beans, runner beans, green beans.

Brassicas: broccoli, calabrese, cauliflower, Brussels sprouts, cabbage, kale, kohlrabi, swede, turnip.

Onions: onions, leeks, garlic, shallots, spring onions.

Roots: beetroot, carrot, chicory, jerusalem artichoke, celeriac, fennel, parsnip, potato, salsify, scorzonera. Plus other related crops such as tomatoes, aubergines, peppers and celery.

As potatoes take up such a large area of ground they are often placed in a group of their own. Each group can also included a handful of intermediate catch crops (in keeping with the main crop group), such as beetroot with Roots, spring onions with Onions and radishes with Brassicas.

Vegetables that do not fit into these main groups such as squashes, courgettes, cucumbers, salad leaves and sweetcorn can be used to form a 'miscellaneous' group or fitted-in where there is space.

If you are growing vegetables in containers, change the compost every year to avoid a build-up of pests.

In small gardens, where only a few vegetables are grown, it is best just to avoid growing a particular group or individual crop in the same place for two or three consecutive years.

The basic idea is that if a plant is not grown on the same ground for three or four years there is a good chance
that any crop specific diseases will die out. Unfortunately, with small gardens and small vegetable plots the distances between the various crops are so small, that the disease can easily travel from one area to another, in any case. Therefore if you get a really pestilential infection, such as club root in brassicas, growing your brassicas in a different part of the garden may not be effective and the only sure method of eliminating this disease would be to simply avoid growing brassicas for several years.

Making a Simple Crop Rotation Plan

A typical four year rotation could be as follows:

BED 1 Legumes Brassicas Roots & Onions Potatoes
BED 2 Potatoes Legumes Brassicas Roots & Onions
BED 3 Roots & Onions Potatoes Legumes Brassicas
BED 4 Brassicas Roots & Onions Potatoes Legumes

The above example plan ensures that related crops do not get planted in the same section of ground within a three year period, thus reducing pest and disease build-up in the soil. However, the precise makeup of your plan will depend on what vegetables you want to grow and the amount of space available. For example if you don't grow a large volume of potatoes then another method of four-crop rotation could be 1: legumes, 2: brassicas, 3: root crops, 4: miscellaneous; or just 1: legumes, 2: brassicas, 3: roots for a three year cycle.

Whatever crop rotation plan you choose, draw it out on a sheet of paper and pin it up in the garden shed to help you remember what should be planted where. It is also a good idea to physically mark-out the segregated planting areas help to visualise where each group of crops is to go.

Applying Manure and Lime

Root vegetables may fork (split roots) if grown on freshly-manured ground. Whereas brassicas will benefit from it, so only apply well-rotted manure or fresh garden compost on the bed where you plan to grow brassicas, then grow root crops on this ground the following year. Legumes, such as peas and beans, actually put nitrogen into the soil, so you can usefully follow these the next year with leafy crops that take nitrogen out of the soil.

Brassicas require a non acid soil, so apply lime to this bed if necessary. Note: Do not lime the soil at the same time as adding manure, as the two may react together.

A general purpose fertiliser can be applied a few weeks before planting for most crops.

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