One of the most common questions asked is, "Do I really need to rotate my garden crops?"
This is especially a problem in smaller, home gardens, but the answer is always yes! There are three main reasons to rotate the crops in you garden: disease, pests and nutrient use.
Many disease organisms are soil-borne and can build up in the soil waiting year after year to attack the new plants. Disease problems often increase when the same crop is planted in the same area in successive years. By putting in a new crop that is not susceptible, a particular disease there will be less chance for the disease to last through the year. Annually rotating your vegetables in the garden may not eliminate your disease problem, but it can help reduce the severity of the diseases.
Pest control can also be helped with crop rotation. A good example of pest problems would be leaf miners. The adult version of this pesky bug lays eggs on the underside of the spinach leaves. The eggs hatch and the larva burrows inside the leaves of the plant destroying the leaf. Eventually, after it's eaten its fill, the larva falls to the ground and hides in the soil, waiting for next year's crop. You can see how a pest like this could multiply year after year.
Some plants are what are called "heavy feeders" (corn, lettuce, broccoli, tomatoes). This means they use up a lot of nutrients in the soil. Most heavy feeders are particularly fond of nitrogen, so planting these heavy feeders in the same spot for even two or three years drastically depletes your soil nitrogen. Your soil needs time to recover from planting them, so you should rotate away for at least three years and take extra care to add back nitrogen to your soil after planting corn.
Nitrogen can be replenished organically by adding compost to the soil, planting high nitrogen cover crops or even by adding grass clippings to the soil. Another way to add nitrogen is to plant a member of the legume family (peas, beans or clover). Legumes have the amazing ability to be able to "fix nitrogen" from the air. This means with the help of some special organisms in their root system, they are able to add back nitrogen to the soil. So when you plant legumes in a spot, you can expect a nitrogen boost in the soil.
Plants that follow legumes will see the benefits of this added nitrogen. You can rotate them around your garden to help improve your soil. In the fall, don't pull the plants up - instead, clip them off and let the roots decay in the soil. They will leave behind nitrogen ready for next year's plants to make use of.
Vegetable crops in the same botanical family are often susceptible to the same diseases and insects. For crop rotation to be effective, gardeners should not plant vegetables belonging to the same plant family in the same location for two or three years. I know crop rotation in a small garden is difficult; however, home gardeners should rotate their vegetable crops as best they can.
Here are some major family groupings. Nightshades: tomatoes, peppers, eggplant and potatoes. Cucurbits: squash, cukes, pumpkins, melons and gourds. Brassicas: broccoli, cauliflower, cabbage, kale, Brussels sprouts, turnips, radishes, Chinese cabbage, mustard greens and collards. Legumes: beans, peas and soybeans. Alliums: onions, leeks and garlic. Umbellifers: carrots, parsnips, fennel, parsley and dill.
To do a proper job of crop rotation, you are going to need a plan. Don't rely on your memory! To do this, you need to start writing down what you have planted where. Hmmm, maybe I have mentioned having a garden plan before.
Happy gardening!
Peter Sutter is a lifelong gardening enthusiast and a participant in the University of Missouri Extension's Master Gardener program. Gardening questions can be sent to [email protected].