What is crop rotation?

What is crop rotation?
Crop rotation is an important aspect of organic gardening. It helps to prevent the build-up of soil borne diseases by rotating the families of plants grown in an area over a 3 or 4 year cycle. Some plants are especially prone to soil diseases and these problems will persist in the soil if the same species are grown for 2 or more years in a row.
Certain plant groups will also tend to use up specific nutrients from the soil so you may end up with a soil that is deficient if you don't change their growing position.

The rotation system is best for larger gardens, ideally four beds are needed, however it is important to use in small areas too, especially for tomatoes and potatoes as they are prone to many diseases which can persist in the soil.

There are some advantages in planting one crop after another where one will benefit from the actions of the previous crops, for example a good cover crop turned into the soil will add nutrients for the following season. Legumes add nitrogen to the soil so they should be followed by a nitrogen hungry crop such as silverbeet, leafy brassicas or potatoes.

Four bed crop rotation:
Legumes/other pod crops > Alliums > Solanums/root and tuber crops > Brassicas > back to the beginning.

If you aren't sure what those food family members are:
Legumes - peas and beans: sugarsnap/snowpeas, broad beans, lima beans, French and climbing beans
Other pod crops: okra.
Alliums - the onion family: brown, red or white onions, leeks, shallots, garlic, spring onions.
Solanums - the potato family family: tomatoes, potatoes, capsicum, chilies, eggplants.
Other roots/tubers: parsnips, carrots, swedes, turnips, kohl rabi, celery.
Brassicas - the cabbage family: cauliflowers, broccoli, cabbages, radishes, brussels sprouts, kale, most Chinese vegies, etc.

Another important thing to remember with crop rotation is that you need to keep track of what you have grown in the different areas each year so you can have a succesful system. If you have a large garden with four beds it will be much easier to keep track.

Vegetable growing seasonal calendar.
As a general and very rough rule those vegetables that produce a fruit (eg, capsicum, pumpkin, tomato, corn, eggplants) are summer growing, heat-loving varieties, while the more leafy plants (includes most of the cabbage family) will be a cooler season crop.

Year round vegetable varieties.
Some vegetables can be grown year round. Carrots and lettuces have varieties for each season; radishes, spring onions, beetroot and silverbeet can be planted regularly for an ongoing supply. Many of the Chinese leaf vegetables can be grown year round, as they need to be grown quickly and replanted regularly for a good supply. Strawberry varieties seem to be around at most times of year these days, too.
Many of the popular herbs such as parsley, basil, chives, coriander, mizuna can be repeat sown.

Summer crops need to be planted in mid to late spring. Vegetables to sow and grow at this time of year include the pumpkin family, such as watermelons, honeydews, zucchini and cucumbers, tomatoes, capsicums and chillies, eggplant, beans, corn. Leeks need to be sown in late summer to allow a long growing season.

Winter crops: Some plants cannot take the heat and will dry up or go to seed quickly in Perth's high summer temperatures.
English spinach likes the cooler weather, as do peas, broad beans, cabbages, cauliflower and co, kale, brown onions, parsnip, turnips and swede.


reference:
Digger's Club "Grow what when" planting guide. (2007).
Readers Digest Encyclopedia of Gardening. 1995. Reader's Digest, Sydney, Australia.
Planting guide (2002): humusbeings.blogspot.com (Accessed 13/01/2010).