What:

“The principle of crop rotation is to grow specific groups of vegetables on a different part of the vegetable plot each year. This helps to reduce a build-up of crop-specific pest and disease problems and it organises groups of crops according to their cultivation needs. “ (RHS)

Why:

Soil Health and Fertility
Soil provides plants with the water, air, and nutrients they require for growth; so healthy soil equals healthy plants. As different crops require different proportions of nutrients over the annual growing season, systematic rotation helps prevent nutrient deficiencies from occurring.

Pest Disease and Control
Specific plant families are susceptible to specific pests and diseases. If left unchecked, spores, eggs, and pests can infest a particular soil site and perpetuate the damage to both current and future crops. By rotating crops around different sites, the pests and diseases are deprived of their host plant, thereby inhibiting their population expansion. Common problems that can be avoided by rotation include club root in brassicas and onion white rot.

Weed Control
Crops with dense, leafy foliage can suppress weed growth, which removes competition between plants for soil nutrients and helps reduce garden maintenance.

How:

“ Fruits, Shoots and Roots” ~ Alison, Head Gardener, Veg on the Edge

Example: Three-Year plan for a Specific Plot

YR #1: Nutrient rich soil – Fruits e.g. beans, tomatoes.
YR #2: Nutrient medium soil – Shoots e.g. cabbages, kale.
YR #3: Nutrient low soil – Roots e.g. carrots, parsnips.

The RHS also gives a traditional three-year rotation plan using the following groupings, with potatoes and brassicas as the important crops:

Brassicas ~ sprouts, cabbage, caulis, kale, kohl-rabi, oriental greens, radish, swede, turnip.
Legumes ~ peas, broad beans.
Onions ~ onion, garlic, shallot, leek.
Potato ~ potato, tomato.
Roots ~ beetroot, carrot, celeriac, celery, Florence fennel, parsley, parsnip & other root crops.

Year one
Section one: Potatoes
Section two: Legumes, onions and roots
Section three: Brassicas

Year two
Section one: Legumes, onions and roots
Section two: Brassicas
Section three: Potatoes

Year three
Section one: Brassicas
Section two: Potatoes
Section three: Legumes, onions and roots

How to do a four-year rotation

Using more legumes (which take up a lot of space) and onion-type crops:

Year one
Section one: Legumes
Section two: Brassicas
Section three: Potatoes
Section four: Onions and roots

Year two
Section one: Brassicas
Section two: Potatoes
Section three: Onions and roots
Section four: Legumes

Year three
Section one: Potatoes
Section two: Onions and roots
Section three: Legumes
Section four: Brassicas

Year four
Section one: Onions and roots
Section two: Legumes
Section three: Brassicas
Section four: Potatoes

Perennial vegetables (e.g. rhubarb, asparagus) do not fit into the rotation. Certain annual crops such as cucurbits (courgettes, squashes, pumpkins, marrows, cucumbers),  French and runner beans, salads (endive, lettuce, chicory) and sweetcorn are grown wherever convenient but avoid growing them too often in the same place.

Whilst focusing on one or two primary crops it is also possible to Intercrop (grow another crop in the space between the rows) and Catch Crop (a fast-growing crop that is grown simultaneously with, or between, successive plantings of a main crop and is harvested before the main crop) without disturbing the crop rotation. Radishes, turnips, and salad leaves are good examples of both.

Thank you to Alison for her help and advice on this topic.

Additional information courtesy of The RHS ~ https://www.rhs.org.uk/advice/profile?pid=124