January is a good time to think about your crop rotation and what quantities you will be growing. What was a success last year, what did you have a glut off – and what did no one like? (Bridget - what is wrong with courgettes?) Taking photos throughout the year is a good idea too as it is so easy to forget what everything looked like on a dark January day!
What is Crop Rotation?
Crop Rotation is the practice of growing specific groups of vegetables on a different part of the vegetable plot each year. This helps to reduce a build-up of crop-specific pest and disease problems and it organises groups of crops according to their cultivation needs.
Benefits of Crop Rotation
- Soil Fertility: Different crops have different nutrient requirements. Changing crops annually reduces the chance of particular soil deficiencies developing as the balance of nutrients removed from the soil tends to even with time.
- Weed control: Some crops, like potatoes and squashes, with dense foliage or large leaves, suppress weeds, thus reducing maintenance and weed problems in following crops.
- Pest and Disease Control: Many pests and diseases are plant family specific. By rotating crops between sites these pests tend to decline in the period when their host plants are absent which helps reduce build-up of damaging populations of spores, eggs and pests. Common diseases that can be avoided by a good rotation include clubroot in brassicas and onion white rot.
Vegetables are divided into different families depending on the characteristics that they share.
Umbelliferae - Celery, Parsley, Carrot, Celeriac, Parsnip
Allium - Chives, Garlic, Leek, Onion, Shallot
Solanaceae - Potato, Tomato, Pepper, Aubergine
Legumes - Pea, Broad bean, French bean, Runner bean
Cruciferae/Brassica - Brussels sprouts, Cabbage, Cauliflower, Broccoli, Swede, Radish, Turnip, Rocket, Kale, Khol-rabi
Cucurbitaceae - Pumpkin, Courgette, Squash, Melon, Marrow
Chenopodociaceae - Spinach, Beetroot, Swiss chard
Compositae - Lettuce, Endive, Globe artichoke, Chicory, Jerusalem artichoke
For a four year rotation group your crops as below
1) Potato family: Potato, tomato.
2) Legumes: Peas, broad beans, french beans, runner beans etc.
3) Brassicas: Brussels sprouts, cabbage, cauliflower, kale, kohl-rabi, oriental greens, radish, swede and turnips.
4) Roots: Alliums, beetroot, carrot, celeriac, celery, Florence fennel, parsley, parsnip and all other root crops.
Move each section of the plot a step forward every year so that, for example, brassicas follow legumes, onions and roots, legumes, onions and roots follow potatoes and potatoes follow brassicas.
Why is this a good rotation?
- Brassicas follow legumes: Sow crops such as cabbage, cauliflower and kale on soil previously used for beans and peas. The latter fix nitrogen in the soil, whilst the former benefit from the nutrient-rich conditions created.
- Potatoes also love nitrogen-rich soil, but should not be planted alongside brassicas as they like different pH levels.
- Very rich soil and roots don't mix: Avoid planting root vegetables on areas which have been heavily fertilised, as this will cause lush foliage at the expense of the edible parts of the plant. Therefore parsnips/carrots etc are grown after the brassicas – a very nutrient heavy crop.
Points to remember
- Plan your crop rotation before the growing season starts, and mark out the plots on the ground so you know where to plant each crop.
- Rotations can be as long as you want.
- Brassicas, onions and potatoes should ideally have four years between crops.
- Green manures can be used to fill up space on beds and also to protect the soil over the winter.
- If you have sufficient space you could include a fallow year in the rotation.
- Certain annual crops such as cucurbits (courgettes, pumpkins, squashes, marrows, cucumbers), salads (endive, lettuce, chicory, rocket) and sweet corn can be grown wherever convenient, merely avoiding growing them too often in the same place.
- Perennial vegetables (such as rhubarb, asparagus, sea kale) do not fit into the rotation.
- Aim to always keep the soil covered, either with a crop, a mulch or by planting Green Manures.
- Never leave soil uncovered - aim to have 100% groundcover, 100% of the time.