A crop rotation helps you decide what to grow where in order to avoid soil depletion and the opportunity for pest problems to get really serious. Using one is easy enough – but the basis of any crop rotation is…notes.
Regardless of whether you’ve been growing your own food for ages or if this is your first year doing so, one of the most important things you can do for the long-term health of your garden is to make notes. Seed sowing dates and conditions, potting soil, temperatures, germination length, everything. After all, you won’t know what’s useful until you need it. Note when you plant things out, harvesting dates, length of harvest, and of course pest problems. And, most important of all, keep a very clear record of where you grew what.
If you grow the same thing in the same place, year after year, vital nutrients and minerals important to the healthy growth of that particular plant will be used up. And imagine how resident pests will feel when you put their favourite food right back next to them – again! You would be getting fan mail if they could write – but you won’t be getting very much in the way of crops!
Crop rotations are helpful anywhere, but are particularly important in the confines of a polytunnel or greenhouse. If you get a pest problem inside one of those, it will be much more difficult to get rid of.
Some people use a 3-year rotation plan, others 4-year. It doesn’t really matter which one you choose – the main thing is to base it on the kind of things you like to grow and eat. There’s no point in growing loads of garlic, for example, if neither you or your family like it very much.
In a greenhouse to some degree, but especially in a polytunnel – where beds are more likely to remain filled right through the year, even in winter – you may want to design a seasonal rather than annual rotation plan.
The list of crops is then divided based on certain characteristics. Brassicas, for example, usually form a single group, as they all share particular things in common: they are all heavy feeders and have similar pest and disease problems.
Here’s an example of a 4-season rotation for a polytunnel:
Group A is the really hungry crops – the brassicas: Cabbage, cauliflower, daikon, kohlrabi, pak choi, radish, rocket, sprouting broccoli and turnip.
Group B contains the legumes and also some additional hungry crops – courgettes for example – all of which have a very different character to the brassicas: Broad beans, French and dwarf French beans, chard, courgettes, cucumbers, lettuce, melon (and watermelon), peas, spinach and sweetcorn.
Group C contains the tomato family and one or two others. Again, these generally share characteristics which set them apart from the other groups: Aubergine, garlic and elephant garlic, onions, peppers, potato, spring onions, sweet potato, tomato.
Group D is root crops, plus one or two others. These aren’t as hungry as the other groups and in the case of carrots, for example, fresh compost should not be added as it can make the roots fork. Beetroot, carrots, celeriac, celery, coriander and fennel.
Plants absent from the list are salad crops. These are great space fillers and can be put here and there, wherever there’s room, in any of the groups.
A rotation plan can be found on page 16 of ‘How To Grow Food In Your Polytunnel’. Otherwise, just draw four layouts of your tunnel beds, one each for summer, autumn, winter and the hungry gap. First play around with positioning the various groups for each season, and then plan the individual plantings for each group. Avoid having the same group in the same place more than twice in a row, i.e. summer and autumn is OK, but don’t continue with the same group for winter. In general, feed with compost between groups with the exception of Group D. This should follow group A, but with no fresh compost added to the soil beforehand.
And, of course, keep your eyes open for pests!