Many home vegetable gardeners have limited garden space, resulting in the same plants being grown in the same places year after year. This common practice leads to the buildup of soil-borne pathogens (which cause diseases such as Southern blight, bacterial wilt, Sclerotinia stem rot, etc.), insects (wireworms, cutworms, rootworms, etc.), and nematodes in the garden. Crop rotation is a simple cultural practice that can help manage many of these issues.
The principle of crop rotation is to plant a crop in a different location each year. Rotating crops disrupts pathogens, insects, and nematodes by removing the host required to complete their life cycle. Pests may remain in the soil for quite some time, waiting for their required host to be planted; therefore, a crop should only be grown in the same spot a maximum of once every three years. While a three-year rotation is the minimum recommended, a four or five-year rotation will be even better at reducing the buildup of soil-borne pests.
A good example of a three-year rotation includes growing beans (year 1), followed by tomatoes (year 2), and sweet corn (year 3) before planting tomatoes in the same spot again the following year.
The best way to ensure proper rotation is by having multiple separated garden plots or beds. Some gardeners have a single garden plot divided into multiple zones, and crops are rotated between the zones. A major flaw in this method is the plot is usually tilled or cultivated all at once, mixing soil between the zones. Moving the soil around in this manner also moves nematodes and pathogens, negating the effects of crop rotation.
Planning Crop Rotation
It’s often difficult to remember important details of the garden from year to year; therefore, keeping records can be helpful. This will also aid in planning a successful rotation. Keep notes on which crops were planted, where and when they were planted, and any pest events noticed during the season.
When following a 4-year rotation, try to plan all four years ahead of time. If changes are made as time goes on, be mindful of the plants grown in the bed in previous years. The table below is a sample crop rotation that has been planned out for the next four years.
Sample 4-Year Crop Rotation
|Year||Bed A||Bed B||Bed C||Bed D|
It may also be helpful to draw a diagram of the garden, labeling each bed or garden plot. Beds and plots may be designated by numbers, letters, or names, so long as they are simple and easy to remember.
When planning crop rotation, it is important to consider the plant family to which the crop belongs. Crops within the same family are often susceptible to many of the same pests; therefore, a proper rotation should rotate plant families.
The beans, tomato, sweet corn rotation referenced previously includes three different plant families: Leguminoseae (beans), Solanaceae (tomato), and Poaceae (sweet corn). In contrast, rotating tomatoes, peppers, and eggplant is not recommended, as all three are members of the Solanaceae family and are susceptible to many of the same pests. The table below shows the families to which the major food crops grown in South Carolina belong.
Plant Families of Vegetables Grown in South Carolina
|Plant Family||Common Food Crops Grown in SC||Other Notable Members|
|Spinach, beet, Swiss chard||Pigweed, celosia, quinoa, sugar beet|
|Onion, leek, garlic, chive||Daffodil|
|Carrot, parsley, celery, cilantro (coriander), fennel, dill||Cumin, poison hemlock|
|Lettuce, artichoke (hearts), Jerusalem artichoke, endive||Sunflower, zinnia, marigold, chrysanthemums, ragweed, dandelion, daisy, stevia|
|Collard, kale, cabbage, broccoli, mustard, turnip, radish, cauliflower, Brussel sprouts, arugula||Canola, horseradish, sweet alyssum, wasabi|
|Morning Glory Family
|Squash, zucchini, cucumber, watermelon, cantaloupe, honeydew||Luffa, gourd, pumpkin|
|Mint, basil, rosemary, oregano, sage, thyme||Salvia, lavender, catnip|
|Bean, pea, peanut||Soybean|
|Sweet corn||Wheat, oats, rye, barley, sugar cane, rice|
|Tomato, pepper, eggplant, Irish potato||Tobacco, petunia|
Limitations of Crop Rotation
Though crop rotation can be an important tool, it isn’t perfect. Some pests and diseases have an extensive host range and can affect crops across multiple families. When planning rotations, research the alternate plant hosts of pests and diseases that affect the crops being grown. For example, Southern blight (Athelia rolfsii) has been reported on over 500 different plant species, including tomatoes, peanuts, collards, strawberries, and carrots, all of which are in different plant families. IF Southern blight is a problem, crops in the family Poaceae, such as sweetcorn, are good rotation partners as they are not hosts. HGIC fact sheets are a great place to find information about the major pests and diseases associated with each crop.
As mentioned previously, soil movement between beds may spread pathogens and nematodes, negating the effects of crop rotation. Soil may be moved on shovels, hoes, tillers, wheelbarrow tires, and even shoes. To avoid soil movement, thoroughly wash all soil particles from gardening equipment, shoes, and tires when moving from one bed to another.
Lastly, crop rotation is only an effective management strategy for pests that are predominately confined to the soil (or soil-borne). Pathogens that are dispersed by wind-blown spores or insects that over-winter on weeds are largely unaffected by rotation. This is an excellent reason to keep records of pest events that occur in the garden and learn the life cycles of those pests to better manage them in the future.