Why crop rotation earns its keep on a small plot

When every square metre counts, it's tempting to grow the same crops in the same spot year after year. But on a compact allotment, that's a fast track to tired soil and persistent pests. Crop rotation — moving crops from one bed to another each season — interrupts the life cycles of soil-borne problems like clubroot in brassicas, white rot in onions and garlic, and potato cyst eelworm. It also balances soil fertility: hungry crops follow nitrogen-fixing ones, and light feeders follow the heavy feeders. The result is a plot that stays productive without relying on ever more chemicals or bought-in compost.

Know your crop families

Rotation works best when you group plants by botanical family, because relatives tend to share pests and diseases. Here are the main groups you'll be juggling on a UK allotment:

• Legumes: peas, broad beans, runner beans, French beans. They fix nitrogen from the air and leave it in the soil.
• Brassicas: cabbages, kale, broccoli, sprouts, swede, turnips, radishes, rocket. They love nitrogen and lime, and suffer from clubroot.
• Alliums: onions, garlic, leeks, shallots, chives. They dislike fresh manure and are prone to white rot.
• Roots: carrots, parsnips, beetroot, celeriac, parsley root. They need deep, stone-free soil and little nitrogen.
• Potatoes: also tomatoes, peppers and aubergines (though these usually live in the greenhouse). Potatoes like rich soil and can suffer from blight and eelworm.
• Others: courgettes, squashes, cucumbers, sweetcorn, lettuce, spinach, chard. These can be slotted in wherever there's space, but keep them moving too.

The classic four-bed rotation, adapted for a compact plot

If you can spare four beds — even narrow ones — the traditional four-course rotation is a reliable framework. Here's how it runs:

• Year 1, Bed A: Legumes. Add compost or well-rotted manure the previous autumn. Plant peas and beans.
• Year 2, Bed A becomes Bed B: Brassicas. Lime the bed in winter, then plant cabbages, kale and broccoli. They'll use the nitrogen left by the legumes.
• Year 3, Bed B becomes Bed C: Roots and alliums. No fresh manure here — it makes carrots fork. Onions, garlic, carrots, parsnips and beetroot all do well after brassicas.
• Year 4, Bed C becomes Bed D: Potatoes. Dig in compost or manure before planting. Potatoes break up the soil and leave it clean for the next round of legumes.

Then the whole cycle shifts on by one bed each year. On a small plot, you can merge roots and alliums into one bed, and grow potatoes in bags or a dedicated bed if space is tight.

Making rotation work when space is tight

Not every allotment has room for four full beds. If you're working with three, or even two, don't abandon rotation — simplify it. A three-bed plan can run: legumes, then brassicas, then roots and alliums, with potatoes grown in large bags or a permanent patch that gets fresh compost each year. If you only have one large bed, divide it into strips and rotate the strips. Vertical space helps too: grow runner beans up canes, train cucumbers up netting, and use pots for garlic and chillies. Keep permanent crops like rhubarb, asparagus and herbs in their own bed, and never rotate them.

Intercropping and catch cropping are your allies. Sow quick salads, radishes or spinach between slower brassicas, or follow early potatoes with a sowing of winter lettuce. Every gap you fill is a chance to confuse pests and make the most of your soil.

Timing, green manures and soil care

Rotation is only part of the picture. After you clear a bed, don't leave it bare over winter. Sow a green manure such as field beans, grazing rye or phacelia. These protect the soil from rain damage, suppress weeds and add organic matter when dug in. If clubroot or white rot has already struck, you may need to rest the affected bed from that family for several years — sometimes up to eight for white rot. In the meantime, grow alliums in containers with fresh compost, and add lime to brassica beds to keep clubroot at bay.

Always add well-rotted compost or manure to the soil, mulch around plants, and avoid walking on beds to prevent compaction. A good rotation buys you time and resilience, but it won't fix waterlogged clay or starved sand on its own.

A sample three-year plan for a small plot

Here's how a compact allotment might look over three years, with three main beds plus a permanent bed for rhubarb and herbs:

• Year 1: Bed 1 — runner beans, French beans, peas. Bed 2 — cabbages, kale, broccoli. Bed 3 — carrots, onions, garlic, beetroot. Permanent bed — rhubarb, mint, thyme.
• Year 2: Bed 1 — brassicas. Bed 2 — roots and alliums. Bed 3 — legumes. Permanent bed unchanged.
• Year 3: Bed 1 — roots and alliums. Bed 2 — legumes. Bed 3 — brassicas. Permanent bed unchanged.

Potatoes go in large bags or a separate small bed that gets fresh compost each spring. Tomatoes and cucumbers stay in the greenhouse, but change their grow bags or soil every year. Keep a notebook — even a rough sketch — so you remember what grew where. Your soil, and your harvests, will thank you.