Vegetable crop rotation is important for a healthy, productive garden, says a University of Missouri Extension horticulture specialist.
Growing a different types of vegetables in the same plot from year to year has many benefits, said Lala Kumar. It avoids the buildup of diseases and pests that can take place when the same or similar crops are planted in the same soil year after year.
“It also promotes good soil health by alternating crops with different nutrient needs, therefore avoiding depletion of any one necessary element present in the soil,” Kumar said.
Crop rotation can also benefit overall soil structure by alternating deep- and shallow-rooting plants, breaking up subsoil and reducing the effects of soil compaction.
A common approach is to rotate crops by botanical families so that individual vegetables from the same family do not follow each other in the rotation. The reason for this is that each family of vegetables has unique effects on growing conditions. “For instance, most vegetables within a given family usually fall prey to the same diseases and insects,” he said.
That makes it important to know the major vegetable families.
The legume family has an important role in crop rotation. Legumes, which include peas and beans of all kinds, are described as “nitrogen fixing” plants. “Legumes collect nitrogen from the air and fix it on the root systems in the form of nodules through a symbiotic relationship with bacteria known as rhizobia,” Kumar said. “Legumes are a great crop to alternate with heavier-feeding plants such as sweet corn and tomatoes.”
Other families common to farms and gardens:
- The goosefoot family includes beets, chard and spinach.
- The mustard family has many members—cabbage, collards, Brussels sprouts, kale, cauliflower, broccoli, kohlrabi, turnip, horseradish and radish.
- The parsley family includes carrot, parsley, celery and parsnip.
- The nightshade family encompasses potato, tomato, eggplant and pepper.
- The gourd family claims the vine crops—summer squash, winter squash, pumpkin, watermelon, cantaloupe and cucumber.
- The composite family includes lettuce, artichoke and Jerusalem artichoke.
- The lily family includes onion, garlic, leek and chives.
- Sweet corn is a member of the grass family.
- Last, but not least, is okra, which is claimed by the mallow family.
“A rotation is easy to plan and use,” Kumar said. First, draw a large circle on paper. Divide the circle into sections as you would cut a pie. The number of sections you have should be equal to the number of vegetable families that you intend to plant.
A simple example would be a garden with four vegetable families: 1) sweet corn (grass family), followed by 2) black-eyed peas and snap beans (pea family), followed by 3) cabbage, broccoli and radishes (mustard family), followed by 4) tomato, pepper and potato (nightshade family).
"To determine what family will occupy the four plots next year, simply rotate the plan clockwise one section,” he said. “Next year the black-eyed peas will be planted where the corn grew this year, and so on. Other more complicated examples can be worked out using the same procedure.”
To make the most of crop rotation, farmers or growers need detailed records of where crops were grown in the past as well as a written plan for how crops will be arranged in the future. Start by making a map of your farm or garden. Label the fields, subfields or plots with names and acreage. Keep a record of crop performance, including any serious pest or soil problems in a field.