Why Rotation Earns Its Keep

Every allotment has its own character. One plot drains beautifully and bakes in July; the next holds water like a basin and grows magnificent kale. Whatever your ground is like, three problems come around each season: soil-borne pests and diseases that build up where their favourite crop keeps returning, nutrients stripped from one bed while another sits idle, and weeds that colonise any bare patch within a fortnight. Rotation deals with all three at once. It is not a rule invented to complicate gardening. It is simply a way of stopping any one crop family making itself at home.

Grow cabbages in the same spot for four years and clubroot will find you. Keep onions on the same bed and white rot moves in. Plant potatoes in the same trench and eelworm multiplies quietly until yields collapse. Move the crops instead, and those life cycles are broken without a single chemical.

The Four Groups Worth Learning

Ignore the botanical Latin if it makes your eyes glaze over. On a working plot, four groups cover almost everything.

• Brassicas — cabbages, kale, sprouts, broccoli, swede, turnips, radish, rocket. Hungry feeders that like firm ground and a dose of lime.
• Legumes — peas, broad beans, French and runner beans. These give back, fixing nitrogen in nodules on their roots.
• Roots and alliums — carrots, parsnips, beetroot, plus onions, leeks and garlic. They want fine, stone-free soil and no fresh manure.
• Potatoes and the hungry crowd — spuds, courgettes, squash, sweetcorn, tomatoes. They reward a good muck.

Keep a note of the families you would not expect: beetroot and spinach are related, as are carrots and parsnips. Rocket and mustard are brassicas, so they belong in that group, not scattered wherever a gap appears.

A Four-Bed Plan, Bed by Bed

Split the growing area into four roughly equal beds, or four blocks within one large bed. Then simply shunt everything along by one position each year.

In year one, put potatoes and the hungry crops on bed one, with well-rotted manure dug in the previous autumn. Bed two takes the legumes. Bed three takes brassicas, on ground limed in winter. Bed four takes roots and alliums. The following year, everything moves one bed clockwise. The potatoes follow the roots, the legumes follow the potatoes, the brassicas follow the legumes and the roots follow the brassicas. After four seasons, you are back where you started, and the ground has had a proper rest from each family.

The order matters more than it looks. Legumes leave nitrogen behind, which suits the leafy brassicas that follow. Brassicas are usually lifted by autumn, leaving clean ground for roots. Roots leave the soil open and weed-free enough for potatoes, which smother what is left.

Squeezing It onto a Small Plot

Three beds is perfectly workable and suits most half plots. Run a three-year cycle: potatoes and hungry crops, then legumes, then brassicas, roots and alliums combined. Keep the lime and the manure on separate beds in the same year, and you will not go far wrong.

If your plot is long and narrow, divide it crossways rather than lengthways — short, wide beds are far easier to net against pigeons and cabbage white butterflies. Raised beds work the same way; four beds of a metre by three will feed two people generously through summer. Where a bed is about to sit empty for six weeks, sow a catch crop of radish, rocket or salad leaves, but remember which group they belong to before you do.

Feeding the Ground as You Go

Rotation handles disease and structure, but somebody still has to feed the soil. Autumn is the moment: spread well-rotted manure or garden compost on the bed due to receive potatoes and hungry crops, and leave the worms to drag it down. Never put fresh manure where carrots or parsnips are going — it forks the roots and invites carrot fly.

Lime the brassica bed in winter, ideally a couple of months before planting, and do not lime the potato bed in the same year, as it encourages scab. In any gap that lasts past August, sow a green manure. Field beans and winter tares will overwinter and can be cut and dug in during spring; grazing rye is excellent on heavy clay; phacelia is quick, pretty and smothers weeds. Keep mustard off the brassica beds, since it belongs to the same family.

Keeping Track Without Fuss

A notebook and a pencil beat any app on a muddy morning. Sketch the plot in January, label the beds, and jot down what went where, when it was sown and how it cropped. Two lines per bed is plenty. Add a note of anything that struggled — the wet corner that rotted your onions, the bed where the sprouts blew — and let next year's plan answer it. Rotate the crops, not the paperwork, and the plot will get easier to manage every season.