The principle underlying crop rotation is that there should be a considerable gap in time between plantings of veggies from the same family in the same place. This helps stop particular diseases building up and also gives the soil a rest from particular burdens placed on it.
Veggies can be divided into the following 8 ‘groups’ (most of which are families or sub-families):
- Legumes (beans, peas, etc).
- Alliums (garlic, onions, etc).
- Roots (beetroot, carrots, celery, parsnip, etc).
- Cucurbits (cucumber, pumpkin, rockmelon, zucchini, etc).
- Solanums (capsicum, chilli, eggplant, potatoes, tomatoes, etc).
- Brassicas (broccoli, brussels sprouts, cabbage, cauliflower, kale, mizuna, pak choy, rocket, etc).
- ‘Anywhere’ (basil, coriander, lettuce, radish, silverbeet, spinach, etc).
- Perennials (asparagus, globe artichokes, rhubarb, etc).
Perennials are not relevant to crop rotation – they should be planted elsewhere. The ‘anywhere’ group are also not relevant – just plant them wherever and whenever you have gaps. So, the ideal is a 6-bed, 6-year rotation for the other 6 groups. If you have fewer beds, then you have to do one or more of three things:
- Combine some things: so, for example, plant alliums and roots in the same bed.
- Omit some things: so, for example, never plant brassicas.
- Plant a cool season crop (e.g. brassicas) followed by a warm season crop (e.g. beans) – or vice versa – into a single bed over the course of a year.
You then have to decide the order of how a bed should change over time. A principle here is that heavy feeders should, where possible, alternate with light feeders. So, for example, alliums (light) – solanums (heavy) – legumes (light) – brassicas (medium) – roots (light) – cucurbits (heavy).
Finally, you have to choose whether the annual rotation should be in Spring or in Autumn.
For a longer discussion of crop rotation, read Robin Gale-Baker’s article on the subject.