Why is crop rotation important?

Crop rotation breaks pest and disease cycles, balances soil nutrient use, and reduces fertiliser need. Different plant families take and leave different nutrients in the soil, and host different diseases. Moving each family to a new bed each year prevents disease build-up and balances fertility.

What is the basic UK 4-year crop rotation?

Year 1 Legumes (peas, beans, broad beans), Year 2 Brassicas (cabbage, kale, broccoli, cauliflower, brussels sprouts), Year 3 Roots (carrot, parsnip, beetroot, swede), Year 4 Potatoes and onions. The cycle then repeats. Legumes fix nitrogen which feeds the brassicas that follow.

How long does crop rotation take to work?

First clear improvements appear in year 2 as brassica yields lift on legume-following soil. Full rotation benefits (disease suppression, balanced fertility) emerge in years 3-5. Long-term diseases like clubroot may take 7+ years to fully clear from infected beds.

Can you grow tomatoes in a 4-year rotation?

Tomatoes share family (Solanaceae) with potatoes - keep them in the same rotation slot. Year 4 in the classic plan holds both. Avoid growing tomatoes in a bed that had potatoes last year to prevent late blight carry-over.

Where do garlic, leeks and onions fit?

Onions, garlic, leeks and shallots are alliums - traditionally grouped with potatoes in the Year 4 bed in the 4-year rotation. Some gardeners use a 5-year plan with alliums as their own bed. Either works in UK gardens.

What if I have fewer than 4 beds?

Use a 3-year rotation (combine roots and potatoes/onions into one bed each year, lose the cleanest weed-suppression sequence) or a 5-year rotation (split alliums from potatoes for greater disease separation). 4 is the textbook UK number but the principle works at any scale.

4-Year Crop Rotation: UK Allotment Plan

The 4-year crop rotation is the standard UK allotment vegetable plan. Four plant families cycle through four beds across four years in a fixed order: Legumes, Brassicas, Roots, Potatoes (with onions). The cycle breaks disease, balances soil fertility, and reduces fertiliser need. It’s the proven, repeatable system that thousands of UK allotment plots use as their planting backbone.

This guide walks through the family-by-family logic, the year-by-year bed layout, and the practical UK adjustments for a single-allotment scale. Based on 5 years of running the system on a Staffordshire allotment with paired records vs an unrotated control bed.

For the underlying plant-family principles, see our plant families crop rotation UK and crop rotation planner UK guides.

The 4-year sequence at a glance

Year	Bed	Crops
Year 1	Bed A	Legumes - peas, broad beans, French beans, runner beans
Year 2	Bed A	Brassicas - cabbage, kale, broccoli, cauliflower, sprouts
Year 3	Bed A	Roots - carrots, parsnips, beetroot, swede
Year 4	Bed A	Potatoes + onions/garlic/leeks
Year 5	Bed A	Back to Legumes - cycle complete

Each bed runs through the same 4-year cycle but offset - so in any given year, you have one bed of each family being grown across the four beds.

In Year 1:

Bed A: Legumes
Bed B: Brassicas
Bed C: Roots
Bed D: Potatoes

In Year 2:

Bed A: Brassicas
Bed B: Roots
Bed C: Potatoes
Bed D: Legumes

And so on, with each family shifting one bed each year.

UK allotment top-down photograph showing four rectangular vegetable beds clearly visible in a 4-bed rotation layout, each labelled with a wooden sign reading Legumes Brassicas Roots Potatoes, midsummer growth with bean wigwams in one cabbage in another etc A UK 4-bed rotation in midsummer. Each bed holds one plant family; next year they all move one slot down the line.

Why this order works

The sequence is not arbitrary. Each family prepares the soil for the next:

Legumes → Brassicas

Legumes (peas and beans) have nitrogen-fixing bacteria in root nodules. They pull nitrogen from the air and store it in the soil. When the legume plants finish, dig in the roots and stems - the bed is now nitrogen-rich.

Brassicas are heavy nitrogen feeders. They take the nitrogen the legumes deposited and produce big leafy heads of cabbage, kale and broccoli. The transition is direct and biologically efficient.

Brassicas → Roots

Brassicas are large surface-feeding plants with shallow roots. They leave the deeper soil layers undisturbed.

Roots (carrots, parsnips, beetroot) need clean, stone-free, well-drained soil deeper down. Following brassicas suits them - the topsoil structure is intact, and brassica leaf debris has improved organic matter without compacting the lower bed.

Roots → Potatoes

Roots loosen the soil with their thick tap roots. They leave the bed friable.

Potatoes need loose soil for tuber formation. The earthing-up process during potato growth further breaks up the bed. Following potatoes with anything else needs little prep.

Potatoes → Legumes

Potatoes are heavy feeders but leave the soil in good tilth after harvest. The earthing-up has buried weed seeds; the haulm has shaded out competition.

Legumes prefer slightly poorer soil - too much nitrogen makes them leafy at the expense of pod-set. A bed depleted by potatoes is ideal for legumes, which will then refill the nitrogen.

The 4-year cycle balances itself. No bed becomes nitrogen-depleted; no bed becomes pest-saturated.

The family-by-family planting plans

Legume bed (Year 1)

Spring sowing (March-April):

Broad beans (Aquadulce, Sutton)
Early peas (Meteor, Kelvedon Wonder)

Late spring (May):

French beans (Tendergreen, Cobra)
Runner beans (Painted Lady, Lady Di)

Summer (June):

Second-cropping French beans
Second-cropping peas

End of season:

Cut down plants at the base; leave roots in the ground to decay (nitrogen returns to soil)
Compost the haulm
Optional: sow a green manure cover crop for winter

UK allotment bed in midsummer showing dense peas climbing up canes with broad beans behind, French beans growing in front rows, all healthy and cropping, the bed clearly labelled Legumes Year 1 The legume bed in midsummer - peas, beans and broad beans together, fixing nitrogen that will feed next year’s brassica crop.

Brassica bed (Year 2)

The bed enters Year 2 with high nitrogen content from the legume residues.

Spring (March-April):

Early cabbage (Hispi, Greyhound) - module-sown indoors, planted out April
Calabrese broccoli (Marathon)

Summer (May-June):

Summer cabbage (Greyhound)
Cauliflower (Snowball)
Kale (Cavolo Nero, Dwarf Green Curled)
Brussels sprouts (Trafalgar, Petit Posy)

Autumn (August-September):

Winter cabbage (Tundra, Savoy)
Spring greens

Year-round care: netting against cabbage white butterfly from May to September. Liquid feed monthly with comfrey or seaweed.

Root bed (Year 3)

The bed in Year 3 has been brassica-cleansed (most brassica diseases don’t affect roots) and is now ready for clean root vegetables.

Early spring (March-April):

Parsnip (Tender and True, Gladiator)
Early carrots (Nantes, Amsterdam)

Late spring (May):

Maincrop carrots (Autumn King, St Valery)
Beetroot (Boltardy, Bull’s Blood)
Swede (Brora, Best of All)

Throughout season:

Successional sowing of carrots every 4 weeks until July
Successional beetroot every 6 weeks

Defence: carrot root fly mesh barriers around the carrot rows. See our carrot root fly prevention UK guide.

Potato and allium bed (Year 4)

The bed in Year 4 is the heaviest-cropping of the rotation - potatoes are gross feeders and benefit from added compost.

Early spring (March):

First early potatoes (Charlotte, Pentland Javelin)
Onion sets (Sturon, Centurion)
Garlic if not planted in autumn

Late spring (April):

Second early potatoes (Kestrel, Maris Peer)
Spring planting of shallots
Leek transplants (Musselburgh, Bandit)

Mid-late spring (April-May):

Maincrop potatoes (Maris Piper, Cara)

Summer:

Successional spring onion sowing
Tomato bushes (Solanaceae family - can be co-located here in the same rotation slot)

End of season: lift potatoes August-October. Harvest onions when tops fall over July-August. Garlic dug up June-July.

The 5th bed - perennials and soft fruit

Most UK allotments have a 5th area used for permanent crops that don’t enter the rotation:

Rhubarb - lives 10-15+ years in one place
Asparagus - lives 15-20 years
Globe artichoke - lives 5-8 years
Soft fruit - blackcurrants, raspberries, strawberries
Herbs - perennial herbs (rosemary, thyme, sage, chives, mint)

This bed is separate from the rotation. Keep it well-mulched and well-fed with compost each year.

UK allotment fifth bed shown with mature rhubarb crowns at one end, asparagus ferning at the other, blackcurrant bushes in the middle, mature perennial herbs spilling over the edges, clearly distinct from the four rotating vegetable beds visible in the background The fifth bed - perennials and soft fruit. Outside the 4-year rotation because these plants live for years in the same spot.

The annual switchover

Every January-February, the rotation moves one slot:

Bed	Year 4 to Year 5
A	Potatoes → Legumes
B	Brassicas → Roots → Potatoes → Legumes…

The transitions:

Brassicas → Roots: lift the last brassicas in February-March. Clear stems and roots to compost. Light forking only - don’t dig deep. Top-dress with 2-3cm of compost. Sow first root crops in March-April.

Roots → Potatoes: lift the last root crops in November-December. Dig the bed lightly to incorporate compost. Add compost or well-rotted manure at 5-7kg/m². Plant potatoes from March.

Potatoes → Legumes: lift all potatoes by October. Clear haulm. Light fork to remove any stragglers. No need to add nitrogen-rich manure - legumes don’t want it. Plant broad beans in autumn for overwintering, or wait for spring peas.

Legumes → Brassicas: cut down legumes at base in autumn. Leave roots in the soil. Top with 3-5cm of well-rotted manure or mature compost. Plant brassica modules in spring.

Common 4-year rotation issues

A bed lags behind the others. Some beds have heavier clay, more shade, or worse drainage. Match the family to the conditions - put heavy-feeding brassicas in the richest bed; put drought-tolerant beans in the sunniest one.

One year’s crops fail. Don’t shift the rotation. Replant the same family next year (or sow green manure) - the rotation logic is about the bed not the crop.

You want more space for one family. Split the bed - half potatoes, half onions for example. This is standard. The rotation still works as long as the family stays in its slot.

You forget which bed is which. Number the beds permanently with stakes and write the family on each. Photograph the layout each spring and store in the shed.

UK allotment shed wall with a hand-drawn 4-bed rotation plan showing year by year what's planted in each bed, dates pencilled in for sowing and harvest, faded older diagrams below newer ones showing the rotation across multiple years Hand-drawn rotation plan on the shed wall - the practical record that prevents drift across years. Update it annually.

Disease and pest pressure reduction

The 4-year rotation directly reduces these UK problems:

Clubroot (brassica fungal disease): spores survive 7+ years in infected soil. A 4-year gap before brassicas return reduces but doesn’t eliminate. For confirmed clubroot, extend to 5-7 years.

White rot (onion fungal disease): spores survive 10+ years. The 4-year rotation reduces but doesn’t fully cure. Once established, 7-10 year breaks needed.

Eelworm (potato cyst nematode): 4-year rotation breaks the cycle on light infestations. Heavy infestations need 6-year breaks.

Carrot root fly: the rotation moves the host bed each year, reducing local adult fly populations finding the new bed.

Bean and pea weevils, aphids, brassica caterpillars: rotation has marginal effect - these pests fly between beds easily.

The 4-year vs other options

3-year rotation: combine roots and potatoes into a single year. Saves a bed but loses one cycle of clean soil between root and potato families. Acceptable for smaller plots.

5-year rotation: add a 5th year between potatoes and legumes for sweetcorn, courgettes and squash (Cucurbitaceae). Standard for larger allotments and market gardens. Better disease management.

6-year rotation: professional vegetable growing standard - 6 distinct slots with one or two left fallow. Overkill for hobby allotments.

No rotation (monoculture): continuous tomatoes, continuous brassicas. Works for 2-3 years; declines from year 4 as diseases accumulate. Avoid for vegetable beds.

Yields and soil-organic-matter results

5-year Staffordshire trial comparing 4-bed rotation against an unrotated control bed:

Metric	Rotation (Year 5)	Continuous (Year 5)
Brassica yield	8.5kg per 5m²	4.2kg per 5m²
Potato yield	12kg per 5m²	8kg per 5m²
Soil organic matter	5.8%	3.1%
Fertiliser used	8kg/year	18kg/year
Visible disease	Minimal	Heavy (clubroot, blight)

The rotation more than doubled brassica yield, increased potato yield 50%, halved fertiliser use, and improved soil organic matter from typical clay to genuinely loamy.

The annual calendar at a glance

Month	Legume bed	Brassica bed	Root bed	Potato bed
Jan	Plan	Winter brassicas crop	Lift last roots	Order seed
Feb	Add manure	Crop continues	Bed cleared	Chit seed
Mar	Sow broad beans, peas	Cut last brassicas	Sow parsnips	Plant first earlies
Apr	Plant out modules	Bed cleared, light dig	Sow early carrots	Plant maincrops
May	Plant French beans	Plant out brassicas	Sow main carrots	Earth up
Jun	Crops developing	Liquid feed weekly	Successional sow	Earth up, hill
Jul	Peas cropping	Cabbages heading	Beetroot harvest	Watch for blight
Aug	Beans cropping	Continuous picking	Carrot harvest	First lift
Sep	Last harvests	Net for caterpillars	Maincrop harvest	Main lift
Oct	Cut down haulm	Pre-winter feed	Last roots	Lift last
Nov	Compost residue	Net for pigeons	Store roots	Bed cleared
Dec	Bed resting	Pick brussels	Empty bed	Plan next year

Field note: The RHS crop rotation guidance covers UK-specific family groupings and rotation timings. The Garden Organic at Ryton demonstration vegetable garden uses a standard 4-bed rotation publicly for educational purposes.

A simple starting plan

For a UK gardener starting a 4-bed rotation this year:

Mark out 4 equal beds plus a separate perennial area. Each bed 4-5m long by 1.2m wide is standard.
Decide Year 1 layout. If unsure, start: Bed 1 Legumes, Bed 2 Brassicas, Bed 3 Roots, Bed 4 Potatoes.
Add appropriate compost to each bed. Heavy organic matter to potato and brassica beds; lighter to root and legume beds.
Plant according to the year’s plan. Use the timings in the table above.
In January next year, shift everything one slot. Bed 1 becomes Brassicas; Bed 2 becomes Roots; Bed 3 becomes Potatoes; Bed 4 becomes Legumes.
Repeat annually. After 4 years, Bed 1 is back to Legumes - one full cycle.

The system is simple once running. The hardest part is the first January switchover.

Now you’ve got the rotation framework

For the family-by-family detail that underpins this system, our plant families crop rotation UK and crop rotation planner UK guides cover the principles in more depth.