1. To prevent the build up of pests & diseases in the soil.
2. To aid soil fertility. (Some vegetables are heavy feeders, some light feeders). Some deplete minerals in the soil & some use less minerals up. Some plants add nutrients to the soil.
3. Suppress & control weeds.
For the purpose of rotation, veg should be sorted into their own groups within each family and rotated in 3, 4 or 5 yearly rotations. (5 being the best).
The groups are:
1. Potato: Tomato, Pepper, Aubergine. (Pepper & Aubergine can also be grown anywhere in the rotation).
2. Legumes: Peas, Broad, Runner & French Beans.
3. Brassicas: Brussel Sprouts, Cabbage, Cauliflower, Kale, Kohle-Rabi, Oriental Greens, Radish, Swede, Turnips.
4. Allium: Onion, Garlic, Shallot, Leek.
5. Roots: Beetroot, Carrot, Celeriac, Celery, Parsley, Parsnips.
The above 5 would be a 5 YEAR ROTATION (5 different areas of ground)
The next year is (1 to 5), (2 to 1), (3 to 2), (4 to 3), (5 to 4).
Some vegetables/plants do not fit into a particular rotation, These are:
Rhubarb, Asparagus, (Perrenials).
Courgettes, Cucumber, Pumpkins, Marrows, Squashes, (Curcubits) (Annuals).
Sweet corn, French Beans, Runner Beans, Endive, Chicory & Lettuce can be planted anywhere but not consistantly in the same piece of ground.
A 4 year rotation which I use would be:
1. Potato Group.
2. Legumes and Alliums.
4. Roots. (Year 2 = 1 to 4, 2 to 1, 3 to 2, 4 to 3) and so on.