How to do crop rotation

Pests and diseases can be a real problem in vegetable plots and one highly effective way of minimising them is to use crop rotation. By annually changing, or rotating, the type of crop you grow in each plot, you will reduce the build up of pests and diseases (such as eelworms, clubroot and onion white rot). It will also help to maintain food levels in the soil as different crops require different proportions of nutrients.

The first records of this system date back to 6000 BC and even in the Bible it recommends observing a ‘Sabbath of the Land’, leaving it fallow every seventh year (Leviticus 25). Crop rotation is frequently used in organic farming to manage the land without relying on artificial controls and fertilisers, and it is equally at home on an allotment or domestic kitchen garden.

Crop rotation can be carried out in all but the smallest vegetable plots. So long as you have the space to have at least 3 separate beds, you can rotate your crops. If you have a smaller area you can still use the principles of crop rotation to take a ‘year off’ growing certain crops to allow pests and diseases to reduce and nutrient levels to recover.

With 3 plots you will need to group your crops as follows:

Group 1 – Potato family (potatoes and tomatoes)
Group 2 – Legumes (peas and broad beans), onions (onions, garlic, shallots and leeks) and roots (eg beetroot, carrots, celeriac, celery, parsley and parsnips)
Group 3 – Brassicas (eg cabbages, cauliflowers, Brussels sprouts, kale, radishes, rocket, kohl rabi, broccoli, oriental greens, swedes and turnips)

If you have 3 separate plots then you would plant them as follows:

Plot 1 Plot 2 Plot 3
Year 1 Potatoes Brassicas Legumes/Onions/Roots
Year 2 Legumes/Onions/Roots Potatoes Brassicas
Year 3 Brassicas Legumes/Onions/Roots Potatoes

In year 4 you return to the year 1 layout, and so on.

The order of planting is important to maximise the benefits of crop rotation. For example, legumes deposit a lot of nitrogen into the soil through the bacteria which grow in their root nodules, which can then be lapped up by the subsequent nitrogen-hungry brassica crops. Potatoes help to break up the soil, which makes it easier for root crops to grow there the following year.

By separating out the crops in this way you can also ensure you prepare each plot over the winter for the coming crop. When the potatoes have been dug up you can lime the plot in preparation for next year’s legumes, do the same again once the legumes have finished to prepare for the brassicas. After the brassicas you can add manure to the bed ready for the potatoes to be planted.

If you have more beds then you can separate out the legumes, onions and roots. For example, if you have 4 plots:

Plot 1 Plot 2 Plot 3 Plot 4
Year 1 Potatoes Brassicas Legumes Onions/Roots
Year 2 Onions/Roots Potatoes Brassicas Legumes
Year 3 Legumes Onions/Roots Potatoes Brassicas
Year 4 Brassicas Legumes Onions/Roots Potatoes

If you have more space then you can separate the onions and roots. Or, if you particularly want to grow root crops, then group the legumes and onions together, so the root crops can have a plot to themselves each year. If you can afford the space then give each plot a rest for a year and grow a green manure on it instead – this will provide extra nutrients when dug in and, in the meantime, will stop weeds building up on the bed.

Some crops don’t need to be included in rotation systems because they have less of a tendency to suffer from built up pests and diseases. Therefore they can be added in with any group, or simply grown wherever you think you’ll have the space each year. These include:

  • French beans and runner beans (or they can be included as part of the legumes group, although they have less of a tendency to attract soil pests and diseases)
  • Peppers and aubergines (or they can be included as part of the potato group as they are from the potato family, although they have less of a tendency to attract soil pests and diseases)
  • Courgettes
  • Swiss chard
  • Sweet corn
  • Spinach
  • Salads (except those listed above)

In addition, perennial crops which require permanent planting can’t be rotated. These include, for example, rhubarb, artichokes, comfrey and asparagus.

Crop rotation should be altered if you do experience a problem such as eelworms, clubroot or white onion rot. Once a disease like this has taken hold, you should avoid planting susceptible plants in that area for some time, up to 20 years in the case of some diseases.