A familiar dance move from many traditions is the twirl that has partners separate and rotate around each other before coming back together. In the country tradition of square dance, the caller directs folks to “do-si-do” and each couple releases hands and steps around back to back in a circle. Dance is not the only venue where separating and taking a new stance can be enjoyable and fruitful; gardens can benefit from a spin now and then, too.
From earliest agricultural times, farmers learned that planting the same crop in the same spot year after year leads to problems. They learned to rotate their plantings for two main reasons—to mitigate pest problems and to maintain soil fertility. Beneath the soil surface lurk some antagonistic organisms that live by invading plants of many kinds. One of the worst is the root-knot nematode. These microscopic pests are normal inhabitants of most soils, but when their populations explode, they can cause plenty of damage. They may feed on soil bacteria, fungi, or other species of nematodes, but when they attack plant roots their presence becomes noticeable in the above-ground portion of the plant as well as causing roots to grow badly. Instead of pale, straight roots, they will be twisted and tangled with lots of warts and bumps.
Besides toxic treatments to minimize (not remove) root nematodes from the soil, there are eco-friendly methods of treatment such as interplanting with plants that exude substances that may kill or at least suppress the nematodes. One of the most successful, though, is to plant a crop of greens from the cabbage family next season. Mustard may be the most effective, but arugula, broccoli, cauliflower, or any cabbage crop will work as well. In severe cases, it may take more than one rotation to make the greatest change. Other resistant crops are all the onion relatives, from leeks to garlic. It’s hard to accomplish actual crop rotation in small gardens, but a little shifting around is definitely beneficial.
Other crops that may benefit by crop rotation are those that require higher levels of different nutrients to thrive. Crops sort into groups by the soil nutrient that they require the most and there is a rotation scheme that can benefit each group. Leafy crops such as lettuce, spinach, Asian greens, broccoli, and such require nitrogen. Fruiting vegetables like tomatoes, eggplant, peppers, cucumbers, melons, and squash need phosphorus to produce well. Vegetables that are grown for their roots, beets, carrots, onions and their like, utilize more potassium. Legumes, all kinds of beans and peas, have the salutary ability to take nitrogen from the air and, with the aid of specialized soil bacteria, incorporate it into their roots. If the plants are turned into the soil after harvest is over, that nitrogen, one of the primary nutrients and necessary for plant growth, is left behind to be used by the next crop. A useful rotation scheme might have cabbage relatives followed by tomato relatives followed by onions and their allies in each garden area.