How does crop rotation work in a vegetable garden?
Crop rotation moves each group of vegetables to a different part of the plot, on a three- or four-year cycle, so problems tied to one family struggle to build up in the soil. In the RHS plan, brassicas follow legumes, onions and roots, and potatoes and tomatoes have their own group: radish, turnip and swede count as brassicas.
By region
| North | Centre | South | |
|---|---|---|---|
| One bed | Often one main crop. Garlic, onion, broad beans and peas take their group even when they sit in the ground over winter. | As in the north, with more autumn sowings that still count in their group. | A long season invites a second crop: that one is another group too, not a repeat of the same family. |
| The gap | Potato and tomato: 3–4 years before they return, with pepper and aubergine, to the same spot. | As in the north. | As in the north. Two crops in one year do not shorten those years. |
The three- or four-year plan is the RHS one, the same from north to south. What changes is how many crops you fit in.
The 3–4 years for tomato, potato, pepper and aubergine are from University of Minnesota Extension, for late blight. The months for each crop are in the planting calendar. Neighbours in the same season, which is a different question, are in companion planting.
The groups
The RHS divides them like this, plus a permanent corner for perennials such as rhubarb and asparagus, which stay outside the plan:
- Brassicas: Brussels sprouts, cabbage, cauliflower, kale, kohlrabi, oriental greens, radish, swede, turnip.
- Legumes: peas, broad beans, French and runner beans. Timing and spacing are in peas and broad beans and when to plant French beans.
- Onions: onion, garlic, shallot, leek. See when to plant onions and how to plant garlic.
- Potatoes and tomatoes. Pepper and aubergine, the RHS writes, suffer from fewer problems and can sit in any group. The months are in when to plant potatoes and when to plant tomatoes.
- Roots: beetroot, carrot, celeriac, celery, Florence fennel, parsley, parsnip. Not turnip and swede: those are brassicas.
Courgettes, pumpkins, cucumbers, salads and sweetcorn, for the RHS, go wherever suits you, without repeating them too often. On courgettes, powdery mildew also arrives on the wind: the guide is courgette powdery mildew.
Three years, or four
The RHS three-year plan, where potatoes and brassicas matter most, on one bed is this: year one potatoes; year two legumes, onions and roots; year three brassicas; then potatoes again. Brassicas follow the legumes. Legumes follow the potatoes. Potatoes follow the brassicas.
The four-year plan, if you grow more legumes and more onions, on the same bed is: legumes, then brassicas, then potatoes, then onions and roots. The sections of the plot move together, each one step a year. Mark them before the season, when you order seed.
On tomatoes and potatoes, University of Minnesota Extension asks for 3–4 years before repeating tomato, potato, pepper or aubergine in the same spot. That is a longer gap than the RHS leaves for pepper and aubergine, which in its plan can go anywhere. For tomato and potato, take the longer gap: the disease is late blight.
What you can expect
The RHS names two diseases where rotation helps: clubroot of brassicas and onion white rot, problems that stay in the soil with their family. It also cites fertility, because different crops take different nutrients, and weed control where potatoes and squashes cover the ground.
It does not fix everything. Courgette powdery mildew travels on the wind, so a new bed can still get it. In a very small garden the RHS says the full plan does not fit: simply avoid the same family in the same spot too often. Small beds and raised beds are in the raised bed guide.
In the app
Every plant in the catalogue lists its companions and rotations, so you can plan your beds with some method.
Frequently asked questions
Are turnips and radishes roots?
In the RHS rotation, no. Radish, turnip and swede sit with the cabbages. Roots include carrot, parsnip, celery, fennel and beetroot.
Do peppers and aubergines follow tomatoes?
The RHS says they suffer fewer problems and can go in any group. University of Minnesota Extension, for late blight, still asks for 3–4 years before repeating tomato, potato, pepper or aubergine in the same spot.
Does autumn-planted garlic count?
Yes. Garlic is in the onion group, even when it holds the bed over winter. Broad beans and peas count as legumes.
What if I only have two beds?
The RHS says the full plan suits every vegetable garden except the very small ones. In a tight space, simply avoid putting the same family back in the same spot too often.
Does rotation stop powdery mildew?
Not on its own. Powdery mildew spores travel on the wind. The RHS still asks you not to repeat cucurbits too often, and the rest is air, water and variety.