Gardening: Crop rotation keeps garden healthier
First, when the same crop is planted in the same place for several years, insect, pests and diseases can build up and wreak havoc on your plants. When the pests’ favorite plants are always available, their life cycles can continue year after year. As a result, the populations grow bigger each year and cause more damage each year. By moving a plant to another part of the garden, the life cycles of the pests and diseases can be broken up and their numbers and the damage they cause can be kept to a minimum.
Second, different vegetables draw different amounts of nutrients from the soil as they grow. Some vegetables like tomatoes, cabbage and beets are heavy users of nitrogen while others like onions, garlic, leeks and carrots are medium to light users of nitrogen. Legumes, like beans and peas, actually replenish nitrogen in the soil through a bacterium in their roots that captures nitrogen from the air and stores it in the plant roots. The nitrogen is returned to the soil after the plants die to feed the next crop.
There are dozens of crop rotation plans available on the internet and it can be confusing to pick the one that will work best for you. A fairly easy way to simplify it is to become familiar with the major vegetable plant families and whether they are light or heavy users of soil nutrients. The onion family is a medium user and includes onion, garlic, and leeks. The tomato family is a heavy user and includes tomatoes, eggplant, peppers, tomatillos and potato. The carrot family is a medium user of soil nutrients and contains carrot, parsnip, dill, fennel and parsnip. The cabbage family is a moderate to heavy user and includes cabbage, kale, broccoli, Brussels sprouts and kohlrabi. The squash family is a moderate user and includes zucchini, summer squash, melons, cucumbers and winter squash. As noted above, the legume family adds nitrogen back into the soil and includes all kinds of beans and peas. Corn is medium user of nutrients.
In general, heavy users of nutrients like the tomato, squash and cabbage families should be followed either by a planting of beans or peas or by medium users, like members of the carrot family, which is then followed by a bean or pea planting. Tomatoes and squash can follow a planting of corn and then be followed by a planting of beans or peas. Onions can be followed by plantings of beets, carrots and radishes.
To help plan your rotations, map out what you planted this year and then map out what you will plant in those same spaces next year. It is not an exact science but in the long run the rotations will distribute resources more efficiently and sustainably and cut down on pest and disease issues.
Pat Munts is co-author, with Susan Mulvihill, of the “Northwest Gardener’s Handbook.” Munts can be reached at pat@inlandnw gardening.com.