If you grow the same crop in the same place year after year soil-living pests and diseases which are specific to that crop will build up in the soil, and levels of soil nutrients will become unbalanced.
There are so many recommended rotations – and some are very complicated and just not possible in a small space. If in doubt, just don’t grow the same thing in the same soil two years in a row (except of course permanent beds such as rhubarb and asparagus).
Some crops may surprise you in that they fall into a rotational group you might not expect. Swedes being a root crop, you would naturally think of them as falling in with the carrots and parsnips but they are actually a brassica. Tomatoes are part of the potato family, and artichokes are in the same family as lettuce!
A basic 3-year rotation is shown in the top image – roots and bulbs, fruit and seed, and leaf and stem. But most gardeners will want to be a little more sophisticated than this and many find a 4-year rotation works well (Potatoes, legumes, brassicas and roots). John Harrison from the excellent Allotment.org.uk website recommends a 5-year rotation:
- Potatoes, followed by mustard green manure and lime following
- Legumes, peas and beans followed by additional lime if required
- Sweetcorn, squashes, pumpkins, courgettes etc
- Roots (carrots, parsnips) and onion family, followed by manure
The upshot is that if you ask 5 gardeners you will be told 5 different rotation plans. Everyone likes to grow different vegetables (if you dont like brassicas then you dont need them in your rotation!), so find one which suits you, but follow these basic principles:
- Keep lime away from potatoes because it increases the chances of them getting scab. Conversely, brassicas like a limey soil. So potatoes should be planted as far away from the application of lime as possible and brassicas can go in to soil that has been limed.
- Potatoes like a rich soil, which is slightly on the acidic side so manure before planting potatoes.
- Root crops such as carrots and parsnips do not want soil that has been manured the previous autumn. It will cause them to fork and split. They tend to like a light soil on the alkaline side so lime can be added if the ph is low (unlikely in Brighton and Hove)
- Beets and onions dont need rich soil either so can fit with the roots in a rotation if needed.
- Legumes like manure. Legumes take nitrogen from the air and store it in their roots (called nitrogen fixing). This nitrogen is valuable for brassicas which often follow legumes in the rotation cycle.
- Where possible, keep plants of the same family together as their requirements will be similar
- lettuce and cut-and-come-again crops can be fitted into any gaps, as can cucurbits (cucumber, courgette, pumpkin and squash) if they dont have a separate section in your rotation.