The Four-Year Crop Rotation

Why Rotate?

Crop rotation is the practice of growing different plant families in different areas of the garden each year, following a structured sequence. It is the single most important technique in the organic kitchen garden, and its neglect leads inexorably to build-up of soil-borne pests and diseases, declining fertility, and poor harvests.

The principle is simple: plants in the same family are susceptible to the same pests and diseases, and they share similar nutrient requirements. Move them each year, and the pest populations that built up last year cannot find their host plants. The soil has time to recover.

The Four Groups

A typical four-year rotation divides vegetables into four groups:

Group 1: Brassicas (cabbage, kale, broccoli, cauliflower, Brussels sprouts, radish, swede, turnip)

• Most demanding of fertility
• Highly susceptible to club root (Plasmodiophora brassicae) — a soil-borne disease that persists for up to 20 years
• Need firm soil and high nitrogen
• Precede with: green manure, then lime to raise pH

Group 2: Roots (carrot, parsnip, beetroot, potato, onion, leek, garlic)

• Light feeders — do NOT add fresh manure
• Fresh manure causes forking in carrots and parsnips
• Potatoes: follow a well-manured bed from the previous year
• Onion family: susceptible to white rot — strict rotation essential

Group 3: Legumes (peas, beans, broad beans, runner beans, French beans)

• Nitrogen fixers — leave valuable fertility for the crop that follows
• Relatively undemanding of added nutrients
• Fix nitrogen through Rhizobium bacteria on their roots — always dig the roots in at season end
• Follow with: brassicas, which will benefit from the nitrogen

Group 4: Potatoes / Miscellaneous (courgettes, squash, sweetcorn, salads, tomatoes, celery)

• Grown on the most fertile ground
• Potatoes clean the ground through earthing up and physical disturbance
• Cucurbits and tomatoes: heavy feeders, benefit from plenty of organic matter

In Practice

Mark your beds 1–4 and rotate clockwise each year. Group 1 follows Group 4, Group 2 follows Group 1, and so on. After four years, each group returns to its starting bed — by which time any club root spores or onion white rot will be greatly reduced.

Historical Bad Practice

Before the understanding of soil-borne disease, monoculture was the norm in large-scale agriculture. The Irish Potato Famine (1845–1852) was the direct consequence of growing a single variety of potato on the same ground year after year — when blight arrived, there was nothing to resist it. Modern intensive agriculture still largely ignores rotation, relying instead on soil fumigants, fungicides, and nematicides — chemical solutions to problems that rotation would largely prevent.