Understanding Crop Rotation on a Small Plot

Why Bother Rotating on a Few Beds?

If you garden on an allotment half-plot or a modest back garden, the idea of a four-year rotation can sound like something written for stately homes with walled kitchen gardens and a team of under-gardeners. It isn't. Rotation matters more, not less, when space is tight, because you cannot afford to let a bed sit idle or lose a season to disease. Moving crops around is simply good housekeeping.

The principle is straightforward: crops in the same plant family tend to suffer the same pests and diseases, and they take similar nutrients from the soil. Grow your cabbages in the same spot every year and clubroot builds up until nothing will grow there. Grow onions in the same bed and white rot sets in. Move them, though, and the soil gets a rest from that particular problem while you put something else to work.

Getting to Know Your Plant Families

Forget Latin for a moment and think in groups you will actually recognise when you are stood at the seed packet shelf.

• Brassicas: cabbages, kale, broccoli, sprouts, swede, turnip, radish, rocket. Hungry, leafy, and prone to clubroot, cabbage root fly and pigeons.
• Legumes: peas, broad beans, runner beans, French beans. These fix nitrogen at their roots and leave the soil richer than they found it.
• Alliums: onions, garlic, leeks, shallots, chives. Slow growers, easy to weed around, but vulnerable to white rot and onion fly.
• Roots: carrots, parsnips, beetroot, celeriac. Happiest in soil that hasn't been freshly manured, or you get forked, hairy roots.
• Potatoes: greedy and bulky, brilliant for breaking up rough ground. Blight is the main worry.
• Salads and leafy greens: lettuce, spinach, chard, and also courgettes, cucumbers and tomatoes if you want a catch-all group.

Four groups is plenty for a small plot. Many gardeners work with brassicas, legumes, roots and alliums, and slot potatoes and salads in wherever there's a gap.

A Simple Four-Bed Plan

Imagine four beds running north to south, or however your plot lies. Label them A, B, C and D in your notebook, not on the ground, because the whole point is that the contents move and the beds stay put.

In year one: Bed A holds legumes, Bed B holds brassicas, Bed C holds roots, Bed D holds alliums. Next spring, everything shuffles one bed along. Legumes go to B, brassicas to C, roots to D, alliums to A. After four years you are back where you started, and no family has seen the same soil twice in that time.

The clever bit is what each group leaves behind. Legumes leave nitrogen in the soil, so the following year's brassicas, which are the hungriest things in the garden, get exactly what they crave. Roots follow brassicas because the ground has been firmed by all that walking around and netting, which suits carrots and parsnips, and it hasn't had fresh muck spread on it. Alliums then tidy up, and the cycle turns again.

Where Do Potatoes and Salads Fit?

Potatoes are the awkward guest at the table. They take up a lot of room and they leave the soil lumpy and full of small tubers you will be digging up for months. On a small plot, the usual trick is to give them their own patch and accept that your rotation becomes a five-year cycle, or to grow them in bags and buckets and take them out of the rotation entirely.

Salads, spinach, chard, courgettes and tomatoes are light feeders and short-lived. Use them to fill gaps left as you clear a bed, or pop a row of lettuce between slower brassicas. They don't need a bed of their own, and they don't cause trouble wherever they land.

If you keep a permanent bed for rhubarb, asparagus, herbs or soft fruit, that's fine. Strip that out of the plan and rotate around it.

Making It Work in Practice

The first year, you will almost certainly find that you have far more brassicas than you thought, or that the roots bed is half empty. Don't panic. Rotation is a guide, not a straightjacket.

• Write it down. A simple pencil diagram of your beds, dated each spring, saves a lot of head-scratching when you are trying to remember where the onions went.
• Keep the drawing honest, including the failures. What grew poorly in one spot is useful information.
• If you are short of room, split the rotation into two halves and swap them each year. It's not perfect, but it's far better than never moving anything.
• Use the winter to lime a bed destined for brassicas, and to spread well-rotted manure on the bed that will take legumes or potatoes the following year.
• Net your brassicas from the moment they go in. Rotation keeps disease down; it does nothing about pigeons.

Finally, remember that bare soil is wasted soil. Sow a green manure such as field beans or grazing rye over winter, or tuck in a quick crop of winter salad, and you keep the worms fed and the weeds at bay while the rotation does its quiet work beneath your feet.