Maintain Healthy Garden Soil with Crop Rotations

Enlarge Image Image Gallery You can plan your crop rotations by using a paper template to simulate your crops and growing areas. There’s ample research showing that crop rotation results in better harvests for potatoes, tomatoes, beans and many other crops. ELAYNE SEARS

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

One of the rules of good organic gardening is to rotate plant families from one season to the next, as best you can, so related crops are not planted in the same spot more often than every three years or so. The purpose of crop rotation is to help the soil maintain a healthy balance of nutrients, organic matter and microorganisms. Of these three, the invisible world of soil-dwelling micro-creatures is the one that most benefits from crop rotations.

Take potatoes, for example. In the course of a season, the fungi that cause scabby skin patches may proliferate, along with root-killing verticillium fungi (which also damage tomatoes and eggplant) and tiny nematodes that injure potatoes. If you plant potatoes again in the same place, these pathogens will be ready and waiting to sabotage the crop. Rotating the space to another unrelated crop deprives the potato pathogens of the host plant they require. Most pests and diseases can damage plants of the same botanical family, but cannot hurt unrelated crops (see “Rotate Your Families: The Nine Main Groups,” below).

What if you don’t follow a crop rotation plan? Field trials in Connecticut and Europe indicate that your potato production will quickly fall by 40 percent, mostly due to disease. According to a seven-year study from Ontario, you could expect similar declines if you planted tomatoes in the same place over and over again. Compared to eight different rotations with other vegetables or cover crops, continuous tomatoes consistently produced the lowest yields. Snap beans that are not rotated will turn into paltry producers, too. In a recent study from Cornell University, snap bean production doubled when beans were planted after corn rather than after snap beans.

In addition to interrupting disease cycles, rotating crops prevents the depletion of nutrients. For example, tomatoes need plenty of calcium the same way beans and beets crave manganese. But the exact benefits of effective rotations vary with crop sequence. Broad-leafed greens are great for suppressing weeds, and the deep roots of sweet corn do a good job of penetrating compacted subsoil. Nitrogen-fixing legumes often take no more nitrogen from the soil than they replace, and their presence stimulates the growth of beneficial soil microorganisms. But in some situations, the “rotation effect” defies easy explanation. For example, we don’t know precisely why potatoes tend to grow well when planted after sweet corn, but they do.

RSS | Comments | E-mail | Print