In the pathway: Organising a sustainable vegetable garden
Crop rotation
Rotating vegetable families over several beds to limit soil pests and diseases and balance crop needs.
Explanation
One classic cycle among others: Legumes → Solanaceae and leaves → Cucurbitaceae → Roots and Alliaceae. It is built on the nitrogen needs and rooting of each family. A thousand-year-old practice (the medieval three-year rotation, the Norfolk rotation in the 18th century) revisited in organic farming and permaculture. Two groups can also each take their own bed, bringing the cycle to 5 or 6 years: the cabbage family (Brassicaceae) and the onion family (garlic, onion, leek), which the RHS counts as separate groups.
Refined definition
Crop rotation means waiting several years, at least 3 or 4 (Jardiner Autrement, SNHF), before bringing the same botanical family back to a bed. Aims: (1) limit the risk of deficiencies (each family draws on a different “palette”), (2) break the cycles of family-specific pests and diseases, (3) balance nitrogen inputs and exports, (4) vary rooting depths to explore the whole soil profile.
Key points
The 4-year cycle of this rotation
YEAR 1: Legumes (bean, pea, broad bean): fix nitrogen from the air through Rhizobium; roots and residues leave part of it for the next crop. YEAR 2: Solanaceae and hungry leaves (tomato, cabbage and other brassicas, salad): use the nitrogen left by the legumes. YEAR 3: Cucurbitaceae (squash, courgette, cucumber): compost at planting, broad soil cover. YEAR 4: Roots and Alliaceae (carrot, parsnip, garlic, onion): less demanding in manure. Alternating taproots and fibrous roots explores the soil at different depths (GAB/FRAB Bretagne). Year 5 = return to the legume. Sources for the principles of rotation: GAB/FRAB Bretagne network, La rotation des cultures en maraîchage, technical sheet no. 16, updated 2015; RHS, Crop rotation; Jardiner Autrement (SNHF), La rotation des cultures au potager, 2023.
Special cases: families with long persistence
BRASSICACEAE (cabbage, turnip, radish, swede, mustard): wait 4 to 5 years between two Brassicaceae crops, 8 to 10 years after an attack of CABBAGE CLUBROOT (Réussir Fruits & Légumes, 2022), whose spores (Plasmodiophora brassicae) can contaminate the soil for up to 20 years (RHS). To keep to this interval, this rotation keeps them all together (the RHS makes them a single group), with the hungry leaves of year 2 or on a dedicated 5th bed. PERENNIALS (asparagus, artichoke, rhubarb, perennial cabbage): no rotation possible, a stable dedicated area.
Mistakes to avoid
ALLIUM + LEGUMES: not a proven mistake. Tradition keeps them apart, but no effect on nodulation has been demonstrated in the field, and the RHS three-year rotation plan even grows them in the same section. REPEATED SOLANACEAE: blight (Phytophthora infestans) common to tomato and potato, do not grow them in succession. REPEATED CUCURBITACEAE: powdery mildew, mosaic virus. ROOTS (carrot, parsnip): carrot fly if repeated too soon.
Watch out for
- • In a small garden (< 50 m²): apply the rotation to the bed, not to the individual crop, 4 beds of 1-2 m² that rotate.
- • Keep an annual plan: without a garden logbook, you forget what you planted 3 years ago. A sketch and a spreadsheet/paper table are enough.
- • Rotation alone is not enough: combine it with intercrop green manures, permanent mulch and varietal diversity for a truly resilient system.
Sources
- Réseau GAB/FRAB Bretagne : La rotation en maraîchage, fiche technique Fruits et légumes n° 16 (agrobio-bretagne.org)
- RHS (Royal Horticultural Society) : Crop rotation (rhs.org.uk/vegetables/crop-rotation)
- RHS (Royal Horticultural Society) : Club root (rhs.org.uk/disease/club-root)
- Réussir Fruits & Légumes (28/04/2022) : « Plasmodiophora brassicae, champignon responsable de la hernie du chou, peut survivre dans le sol plusieurs années »