After designing the overall layout of your garden, the most important element of garden planning (and the part that recurs year after year, which is why you should spend time every winter thinking about it) is crop rotation – planting crops from the same botanical family in different positions each year. It may seem complicated, but there are really just two main approaches to crop rotation – rotating by edible parts, and rotating by crop family.
The Problem With Rotating By General Plant Type
Traditionally, three or four equal sized beds are planted up with crops which are divided into fairly generalized categories, such as fruits, shoots and leaves, with perhaps an extra category for ‘pods' – peas and beans. However, while this system is simple (you can tell where to group a plant based on the part you're going to eat) it does have a major drawback – plants which belong to the same family, and therefore suffer from the same soil-borne pests and diseases and draw the same nutrients from the soil, don't always produce the same type of edible part.
Consider tomatoes and potatoes, for instance. Both are members of the Solanaceae family and both are extremely susceptible to the same type of blight that can wipe out whole crops, but under this system they would be classed as fruits and roots respectively, and so could follow one another and pass on the disease to the next crop.
Using a three-bed rotation, peas and beans commonly occupy a fourth bed and are grown in the same spot each year to avoid having to move cumbersome supports, but while legumes are typically fairly trouble-free there is still an increased risk of a build up of pests and diseases in the soil. Peas and beans are a very useful part of a successful rotation cycle due to their nitrogen-fixing qualities, the benefits of which are passed on to the crops that follow them in rotation.
Rotating Crops by Crop Family
A better way to rotate annual vegetables is to group them by their plant family. This means you can group plants with similar maintenance requirements together – for instance, all plants in the cabbage family are best grown together to make it easier to net them against cabbage white butterfly and birds – and there's no risk of accidentally passing on crop-specific soil-dwelling pests and diseases to the next crop.
If you want to get really geeky about crop rotation – and I do – you can also plan a set rotation order, and a really handy way to do that is to give each plant family a shade relating to the colors of the rainbow, as shown below.
||Alliaceae (onion family) – onion, shallot, leek, garlic|
||Leguminosae (pea & bean family) – all types of pea and bean|
||Brassicaceae (cabbage family) - calabrese, Brussels sprout, broccoli, cabbage, kohl rabi, cauliflower, kale, mizuna, pak choi, radish, arugula, rutabaga, turnip|
||Solanaceae (nightshade family) – potato, tomato, peppers, eggplant|
||Umbelliferae (carrot family) – celery, celeriac, cilantro, fennel, carrot, parsnip, parsley, dill|
||Cucurbitaceae (marrow family) – zucchini, cucumber, marrow, melon, pumpkin, squash|
||Chenopodiaceae (beetroot family) – Swiss chard, perpetual spinach, true spinach, beets |
||Miscellaneous (non-rotation annual crops) eg basil, lettuce, endive, cress, sweet corn, okra, salsify, scorzonera, New Zealand spinach, corn salad, chicory|
Working from the inside of the rainbow out, you can see which plants belong together and which should come next in each bed. The rotation starts with lilacs and blues – onion family plants and peas/beans – which are commonly grown together as they both like soil enriched with compost and take up little space. Once you've harvested your onions and leeks from your first bed, the next crop in that spot would be cabbages, cauliflowers and broccoli and so on, for the first seven categories.
Using this order of rotation is optional but it helps to make sure that the soil is in the correct condition for the following crop.
Plants in the Miscellaneous (grey) category are useful for plugging gaps in your beds as they don't tend to suffer badly from particular soil-borne pests and diseases, and can be fitted in anywhere you have room, although it's still a good idea to move them around from year to year as much as possible, particularly sweet corn which can suffer from rootworms.
Our Garden Planner makes things even easier, as each plant icon is color-coded so you can quickly see at a glance which family it belongs to.