Benefits of Crop Rotation and Green Manure
Gardeners and farmers have been practicing crop rotation since Biblical times. People who worked closely with the land knew that, like people and animals, soil itself must experience cycles of action and rest to be productive.
Rotation is one of the keys to preventing soil erosion, one of the most pressing problems our earth faces today. Along with allowing the soil's natural chemistry to recover, rotation discourages weed and pest depredations without harmful chemicals. Different crops add their particular nutrients to the soil, benefiting the next crop. People usually rotate two or three crops in a particular area of land. Often, certain plants are grown specifically so that they can be plowed under and fertilize the soil.
Even in small to medium-sized vegetable gardens, it is possible to do three- or even four-way crop rotation. Start with a sketch or map of the garden as it is now. Mark off three or four areas in which plants will be rotated. The most important factors are the time periods of years or seasons in which plantings will occur in a particular area and the botanical families to which these crops belong.
Plants from the same family are often susceptible to the same insects and diseases. Once a family has occupied a particular area, it should not be planted there again for two or three years. Certain families should follow others in the rotation, because each family uses a different amount of water and fertilizer and has different beneficial traits. A rough list of families and some examples might include the following. More detailed lists can be obtained online or from a rural extension advisory service.
- Cabbage, cauliflower, broccoli, Brussels sprouts, arugula, kale
- Beans and peas of all kinds
- Potatoes, tomatoes, peppers, eggplant
- Onion, garlic, leek, chive
- Carrots, parsnips, celery, dill, parsley
- Squash, pumpkins, melons, cucumbers
- Spinach, chard, beets
Allow one or more areas to rest by planting cover or "green manure" crops. This can also be done over the whole garden in winter, after the regular growing season has ended. Buckwheat, winter peas, millet, clover, rye grass or winter wheat are frequently used. Growing cover crops is better than simply leaving the area unused for several reasons.
Cover crops stop weeds, aerate the soil and reduce runoff and erosion. They promote diversity and attract helpful insects. Beneficial soil fungi can only reproduce when plants are present, because they grow right into the roots. They extend the root system, supplying additional nutrients.
These plants should be cut down before they begin to flower so that they will not spread or utilize soil nutrients in their own seeds. They are then plowed into the soil to die and decompose for several weeks before putting in a different crop.
Rotation can seem a bit complicated. As with nearly every aspect of working with the earth, it takes patience and practice. Take your time and do as much planning as necessary. You'll see the difference in your healthier, more nourishing vegetables.