Gardening 101: Crop Rotation
This means that you divide your garden bed into three or four parts and each year grow only specific plants in each quarter. Or you can lay out your garden rows and follow a rotation such as the following nitrogen replacement feeders (Legumes; peas and beans), heavy feeders (Brassicas such as cabbage, onions, leeks, corn, squash), light feeders such as carrots, potatoes, and moderate feeders such as tomatoes, peppers and eggplants. Eggplants are the same family as potatoes and tomatoes so try to avoid planting in the same general area.
If you divide your garden into heavy, light, moderate and replacement feeders, you can start to lay out your crop rotation. You also need to take into account that certain plants will harbor diseases from other similar plants. For example, potatoes should not be planted where tomatoes have been grown. Both plants can harbor similar diseases. Another item to take into consideration is companion plantings, or should I say un-companionable plantings. Cabbages, for example, do not like to grow next to onions, garlic or leeks.
So we start laying out our garden. Heavy feeders are corn, cabbages (most of the brassica family), onions (most of the allium family), and winter squash. If you put these in one quarter of the garden (plant the corn between the cabbage and onions), you'll need to add lots of manure before planting. The following year you can replenish the soil by planting legumes which make additional nitrogen. The third year you can plant tomatoes, potatoes and other moderate feeding plants. The fourth year you can grow potatoes, carrots, lettuce and other root crops.
Another way to rotate your plantings is to plant heavy and light feeders such as beans and corn together. The theory is that the beans will grow up the corn, and the bean plants will provide additional nutrients for the corn. I've tried to do this several times and have found that corn grows much faster than the beans and eventually shades the beans. So now I grow a row of corn and a row of beans next to each other and the following year swap their location.
Some specific examples of rotational growing are: carrots suffer from carrot fly and nematodes so grow above-ground crops where carrots and beets grew the previous year. This gives carrot nematodes nothing to grow on in alternate years. If you can make that rotation a three or four year cycle you virtually eliminate carrot nematodes. Plant potatoes where you've grown cabbages the previous year to keep potato beetles under control.
About the only crop you cannot rotate is asparagus. It needs to grow in its own bed for many years, which means you'll have to be vigilant to control asparagus beetles. You will probably find the best way to organically control asparagus beetles is to use a spun fleece crop cover such as Reemay.
In fall, as your garden crops wind down, fill bare patches by sowing winter rye. Winter rye is a cover crop that helps to prevent nutrient loss and in spring, you can turn it under to give your garden an instant nitrogen boost.
By rotating your crops, not only do you keep the land in production, but you cut down on insects, keep replenishing the soil by growing legumes (beans, peas) that fix nitrogen and keep your soil fertile and eliminate run off and soil loss.