What is it and why do it?
Crop rotation is the seasonal rotation of vegetable crops from bed to bed. There are many variants of crop rotation but they all more or less achieve the same thing. The main reasons for crop rotation are to reduce the incidence of disease, break pest cycles and avoid nutrient depletion. Plants are grouped into families that are related to each other, as they are prone to similar diseases and nutrient use, and moved progressively to each garden bed. The ideal crop rotation would be a six bed rotation with a five year gap between crops and a green manure crop with each rotation. Green manure is a legume crop grown to knee-height and then turned back into the soil to add nitrogen and organic matter. However many gardeners do not have the space or the number of beds to do this and there are ways to practice the principals of crop rotation in a smaller garden. For the home gardener the main thing to remember is to avoid planting certain groups of plants in the same spot year after year. The longer you can leave between planting the same crop in the same bed the better!
Vegetables fall into the following main categories:
Brassicas
This group includes cauliflower, cabbage, broccoli, kale, kohlrabi, swede, turnip and radishes. Asian greens such as bok choi, pak choi and wong bok are also included.
Solanum
Includes tomato, eggplant, capsicum and potato.
Legumes
All peas and beans, including broad beans.
Curcubits
This group consists of all pumpkins, squashes, cucumbers, melons and zucchinis.
Alliums
This group consists of onions, garlic, chives, leeks and shallots.
Apiaceae
Carrot, parsnip, celery and parsley.
Other
Lettuce, silverbeet, spinach, beetroot, artichokes, corn
Because most people don’t have a large six bed vegetable garden there are many ways to take advantage of crop rotation and adapt it to your own garden requirements. The above groups can be simplified into four broader categories as follows:
Brassicas and leaf vegetables
Legumes
Alliums
Root and fruit crops
Ideally, in a modified crop rotation schedule solanums should have a four year gap, brassicas three to four years and legumes a three year gap. If you grow tomatoes every year and have only one or two garden beds then try growing them in pots as part of the rotation process.
It is important to remember that crop rotation is only one of many things you can do to minimize pests and diseases in your vegetable garden. The use of compost and mulch, good watering practices and positioning are all important and crop rotation will not help if the basic good practice is not in place.