But it's a little bit more complicated than that. For instance, there's no use in putting in cabbage one year and replacing it in the next with radish, because, weirdly enough, both are brassicas, so they are prone to similar diseases and pests and needs similar levels of nitrogen.
The first step in planning your crop rotation is to work out what food plant family your plant belongs to. Here are the groups along with a list of key vegetables that belong in them. There are some surprises in there (especially vegetables that you would think would count as roots, which are actually in another family):
The Brassica Family
- cabbages
- Brussels sprouts
- cauliflowers
- radishes
- broccoli
- calabrese
- swedes
- turnips
- rocket
- Chinese cabbage
- cress
- kale
- kohlrabi
- land cress
- mizuna
- mustard
- oriental mustards
- pak choi
- salad rape
- seakale
- agricultural mustard
- fodder radish
The Root Family
- carrots
- parsnips
- celery
- coriander
- dill
- parsley
- celeriac
- Florence fennel
- Hamburg parsley
- skirret
- broad beans
- runner beans
- French beans
- mange tout
- peas
- asparagus peas
- lablab beans
- any other form of beans
- alfaalfa
- clover
- fenugreek
- field beans
- lupins
- trefoil
The Potato Family
- potatoes
- aubergine
- peppers
- chilli peppers
- tomatoes
The Beet Family
- beetroot
- chard
- spinach
- Good King Henry
- leaf beet
- red orache
The Allium Family
- onions
- garlic
- leek
- shallot
- chives
- bunching onions
- spring onions
- Welsh onions
The Cucurbit Family
- cucumber
- courgette
- marrow
- melon
- water melon
- pumpkin
- squash
- summer squash
- winter squash
The Lettuce Family
- chicory
- cardoon
- lettuce
- endive
- cardoon
- globe artichoke
- Jerusalem artichoke
- salsify
- scorzonera
Other (also known as orphans) - they don't belong in any other group or really together
- sweetcorn
- sweet potato
- asparagus
- sorrel
- Chinese artichoke
- corn salad
- New Zealand spinach
- sorrel
- summer purslane
- winter purslane
- buckwheat
- grazing rye
So, when you're trying to work out your crop rotation, you should try and include all the vegetables you want to grow in a single bed or area to be rotated so vegetables from the same family don't end up in the same area more than once in your rotation. But, you can include vegetables from more than one family in each bed to be rotated.
But in addition to taking plant families into account, some plants need different levels of nutrients in the soil. Some plants fix nitrogen in the soil (i.e. they add nutrients), some are greedy feeders and need lots of nitrogen, some need lower levels of nitrogen (because if they have too much they grow funny) and some are neutral - i.e. they can take any level of nitrogen and can be planted together with plants of any of the other groups.
The ideal pattern for plants in a crop rotation is that nitrogen fixers should be followed by greedy feeders, which should be followed by plants needing less nitrogen (which should then be followed by nitrogen fixers again). If you can't put nitrogen feeders in before greedy feeders, then you should feed the soil over winter before planting the greedy feeders.
Here are the groups:
| Nitrogen fixer | Greedy feeder | Less nitrogen | Any level of nitrogen |
| legumes, e.g. peas, beans |
brassicas cucurbits potato family alliums sweetcorn |
root family | lettuce family beet family orphans (except sweetcorn) |
Other facts worth taking into account (once you've got to a more advanced level, they might be too much to cope with in your first attempts at rotation):
- If you are repeating a crop, such as potatoes, within a rotation, the two occurrences should be as far apart as possible.
- Potatoes and cucurbits leave a clean soil and are good to precede root crops, which benefit from a clean seed-bed.
- If you need to lime soil for brassicas, don't follow them immediately with potatoes (lime encourages potato scab).
- Although the rules theoretically mean you could grow tomatoes alongside potatoes (as they are both in the potato family), the risk of potato blight spreading to your tomatoes is high enough that it's better to grow them as far apart as possible.
You can rotate crops on a four year or a six year (or presumably also a five year) basis. The crops should be rotated like this in a four year rotations:
| Year 1 | Crop A | Crop B | Crop C | Crop D |
| Year 2 | Crop B | Crop C | Crop D | Crop A |
| Year 3 | Crop C | Crop D | Crop A | Crop B |
| Year 4 | Crop D | Crop A | Crop B | Crop C |
The Royal Horticultural Society's website suggests this crop rotation:
| Year 1 | Legumes | Brassicas | Potatoes | Onions and roots |
| Year 2 | Brassicas | Potatoes | Onions and roots | Legumes |
| Year 3 | Potatoes | Onions and roots | Legumes | Brassicas |
| Year 4 | Onions and roots | Legumes | Brassicas | Potatoes |
If you want to do a six year rotation, here's the pattern:
| Year 1 | Crop A | Crop B | Crop C | Crop D | Crop E | Crop F |
| Year 2 | Crop B | Crop C | Crop D | Crop E | Crop F | Crop A |
| Year 3 | Crop C | Crop D | Crop E | Crop F | Crop A | Crop B |
| Year 4 | Crop D | Crop E | Crop F | Crop A | Crop B | Crop C |
| Year 4 | Crop E | Crop F | Crop A | Crop B | Crop C | Crop D |
| Year 4 | Crop F | Crop A | Crop B | Crop C | Crop D | Crop E |
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