Crop rotation is one of the fundamental principles of successful gardening. Despite many gardeners ignoring it, following it significantly reduces the incidence of disease, improves the soil and increases yields. It's not complicated — you just need to understand the basic rules.
Why rotate crops?
Each plant takes different nutrients from the soil and leaves behind specific diseases and pests. If you grow tomatoes in the same spot for several years running, blight pathogens build up in the soil while potassium and phosphorus reserves become depleted. The result is a progressively weaker harvest and stronger disease attacks each year.
Crop rotation breaks the life cycle of diseases and pests. Blight spores survive in the soil for 2–3 years — if you don't grow any nightshades (tomatoes, potatoes, peppers) in that spot for that period, the pathogen population naturally declines.
Four groups for rotation
The most practical approach is to divide crops into four groups based on their nutrient demands and botanical family:
Group 1 — Heavy feeders
Tomatoes, peppers, cucumbers, courgettes, squash, cabbage, cauliflower, kohlrabi. These crops have the highest nutrient requirements, especially nitrogen. Plant them on freshly manured or composted beds.
Group 2 — Moderate feeders
Carrots, parsley, onions, garlic, beetroot, lettuce, spinach, radishes. Moderate nutrient requirements. Plant after heavy feeders — there are still enough nutrients left from the previous feeding.
Group 3 — Light feeders and soil improvers
Peas, beans, lentils and other legumes. Thanks to their symbiosis with nitrogen-fixing bacteria in their root nodules, they actually enrich the soil with nitrogen. Plant after the moderate feeders.
Group 4 — Potatoes
Potatoes form their own group because they require specific care and leave behind numerous diseases (scab, blight) in the soil. Don't return them to the same spot for at least 4 years.
A practical rotation plan
Divide your growing area into three or four sections. Each year move the crops on by one section:
- Year 1: Section A = heavy feeders, Section B = moderate feeders, Section C = legumes
- Year 2: Section A = legumes, Section B = heavy feeders, Section C = moderate feeders
- Year 3: Section A = moderate feeders, Section B = legumes, Section C = heavy feeders
In autumn, after the legumes, work compost into the soil. In spring the bed is ready for heavy feeders. This cycle repeats and the soil never becomes exhausted.
Botanical families
As well as nutrient requirements, keep an eye on plant relationships. Related species share diseases and pests, so they should not follow each other directly:
- Nightshades (Solanaceae) — tomatoes, potatoes, peppers, aubergines — gap of 3–4 years
- Cucurbits (Cucurbitaceae) — cucumbers, courgettes, squash, melons — gap of 3 years
- Brassicas (Cruciferae) — cabbages, kohlrabi, cauliflower, radishes, broccoli — gap of 3 years
- Umbellifers (Apiaceae) — carrots, parsley, celeriac, dill — gap of 3 years
- Alliums (Alliaceae) — garlic, onions, leeks, chives — gap of 3 years
What to do in a small garden
If you only have one bed, strict rotation is difficult but not impossible. At least observe the basic rule: never follow nightshades with nightshades, or brassicas with brassicas. Compensate by regularly adding compost and mulching, which supports soil micro-organisms and suppresses pathogens.
In a raised bed you can partially alleviate the situation by replacing the top 15–20 cm of compost, but it's better to observe rotation even in a limited space — for example by shifting crops horizontally within a single bed each year.
Green manures
If a bed has space after the main harvest, sow a green manure: mustard, phacelia or clover. These plants cover bare soil, suppress weeds and, once dug in, enrich the soil with organic matter. Mustard also disinfects the soil through its root secretions, reducing some pathogens.
Crop rotation is not a complicated science. All it takes is a plan on paper, a few minutes of thought in winter and discipline at planting time in spring. Your soil and your crops will reward you with a healthy, abundant harvest.