July 2010

My Own Garden: Crop Rotation – Companion Planting for Sustainable Plant Nutrition

Susan Waterman

Crop rotation, a type of companion planting that focuses particularly on nutrition, is an approach to maintaining healthy soil that has been around as long as there have been gardens to grow food. The plants are doing their own work to help each other. The main principle is very simple: in any given area of a garden, try to plant crops from different plant families successively in order to balance the nutrients that are taken from or added back to the soil. If your garden space is 6 feet by 12 feet, for example, the area could be divided into six equal spaces of 2 feet by 6 feet through which crops of different families are rotated annually or seasonally. It’s often convenient to make a simple map of the rotation zones and the crops that will be rotated as needed. Crop rotation can be applied from year to year as crops are changed; or better yet, from season to season as new crops are planted according to the cool or warm season at hand. For example, if you harvest a crop of spinach, instead of replanting the same area with spinach or chard, plant an unrelated crop like zucchini or cucumbers. Besides preventing depletion of nutrients in the soil, crop rotation also helps to prevent the proliferation of disease and pests, which accumulate when the same crop (or a close plant relative) is planted season after season in the same location.

The main information you need in order to have successful crop rotation is to know which plants are related, or not. For example, some of our summer favorites are in the Solanaceae family, and therefore are related: eggplant, pepper, tomato and potato are relatives to each other. Carrots, celery, parsley and parsnip are related (Apiaceae family). The Asteraceae family includes artichokes, chicory, dandelion, lettuce and radicchio. The Brassicaceae includes many popular crops, most of which are cool-season favorites: arugula, broccoli, cabbage, Brussels sprouts, Chinese cabbage, kale, mizuna, totsoi and watercress. Beets, spinach and Swiss chard are all in the Chenopodiaceae family. The family Cucurbitaceae includes cucumbers, squashes, pumpkins and melons. Beans and peas are related, and in the Fabaceae family. Liliaceae family crops include asparagus, garlic, onions and leeks. Claytonia and purslane are relatives. New Zealand spinach and corn are in the Tetragoniaceae and Poaceae families, respectively.

In addition to family relationships, it’s useful to know which crops are heavy feeders and therefore taking more nutrients from the soil; which are light feeders, and which actually give back to the soil. It’s not surprising that most of the veggies we love to eat are heavy consumers. Tomatoes, corn, squash, lettuce and cabbage all take lots of nutrients, especially nitrogen (N) from the soil. In order to replace the nitrogen, in the next round of planting the rotation can be a crop that gives nitrogen back, such as any legume, including peas or beans, or a cover crop like alfalfa, vetch or clover. Other nutrients can be returned to the soil via compost. After a season of heavy feeders, besides nitrogen, it’s good to replenish phosphorous (P) and potassium (K). Then, in the next season or next round of planting, try to plant light feeders such as root crops. Sweet potatoes are light feeders, for example. Green peppers don’t take lots of nitrogen, but they do love other nutrients, though they may be planted after heavy feeders.

Cover crops fit well into year-long rotations, and a full rotation for one zone of the garden may span more than one year if only one crop is being planted each year. Ideally, it is best to wait two or three years before replanting the same crop in a given area, especially if that crop is a heavy feeder, like corn.

Crop rotation is a convenient and practical way to have your plants help you with your garden maintenance!

Susan Waterman has a Ph.D. in botany and over 25 years in sustainable agriculture. For more info, visit www.harvestbyhand.com. Questions? E-mail green@harvestbyhand.com.

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4 thoughts on “My Own Garden: Crop Rotation – Companion Planting for Sustainable Plant Nutrition”

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