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Companion plants

by Professor Stuart B. Hill Department of Entomology Macdonald College

"Do you really believe that you can earn $6,000 a year growing vegetables on just a fifth of an acre?'' one of my colleagues asked me. He was referring to a booklet describing the work of a group of vegetable producers in Santa Cruz, California (Jeavons, 1974).

"Sure," I replied. I had never met them but I had corresponded with them and read their publications, and I had no reason to doubt their claims. I tried to explain that they were using the biodynamic/French intensive method of production, which really only boiled down to the use of raised beds to increase air supply to the roots, and companion planting. The raised beds he could understand but the companion planting left him cold.

Now, if they had been applying synthetic fertilizers, herbicides, and insecticides, it might not have been so difficult for him to comprehend, but they would never let these things anywhere near their gardens. No, they did it instead with companion plants, plus a little compost. While most of us know something of the benefits of well-made compost, few of us are familiar with the advantages and techniques of companion planting. It involves nothing more than arranging the plants in a garden in such a way that they enhance the growth and quality of nearby crops (or, at least, do not antagonize them), provide maximum ground cover, and, if possible, improve the soil.

This approach has much to recommend it. More can be grown per area, and the soil is protected from erosion by wind and rain. The only problem is that it involves more care when planning, seeding or planting, cultivating and harvesting.

While it is rarely known exactly how the plants benefit one another, some generalization can be made. ''Companions" often include plants with contrasting properties: sun-loving and shade-loving ones; plants with deep roots and those with shallow roots; slow-growing and fast-growing plants; heavy feeders and light feeders or crops that incorporate nitrogen into the soil; aromatic plants, which often repel pests, and non-aromatic ones. ones with early flowers that provide pollen and nectar for some insect predators and parasitoids (insects that parasitize insects), and plants that do not bear flowers until late in the season (or that are not allowed to flower); plants that are more attractive to a particular pest than another, i.e. as a trap-crop; and plants that stimulate biological activity in the soil with crops that are heavy feeders.

Some of the relationships probably involve the release of chemical exudates from the roots, which may have a direct effect on other plants or an indirect effect via other organisms in the soil. It may also involve the release of certain gases or odours, which repel pests, from either the roots or the aerial parts of the plant. While the processes involved are difficult to demonstrate, the late Dr. Ehrenfried E. Pfeiffer and Dr. Erica Sabarth of the Bio-Dynamic Association have shown that by adding the juices of pairs of plants to a five per cent copper chloride solution and allowing it to crystallize slowly on a glass plate they were able to predict which plants would be companionate and which antagonistic, based on the appearance of the crystallization patterns or chromatograms. Today they use paper chromatography techniques. Their findings, together with trial and error experiences of numerous gardeners, have been summarized in a pamphlet by Richard Gregg (1943) and in a book entitled Companion Plants and How to Use Them.

Tables 1 and 2 are based largely on these publications. These lists should be used as a basis for experimentation rather than as a guarantee of success. It is particularly important to experiment with the ratios in which to mix plants and the spacings to use between them. For example, bush beans are found to be most beneficial to celery in the ratio of one bean plant to six of celery, and to cucumbers when they are planted around the cucumber patch. Sometimes seeds may be mixed together, as with lettuce, carrots and radish, or they may be grown in adjacent patches, or as a zig-zag with the companion plants in between the zigs (and the zags)!

My first contact with companion plants was when I was four or five and I walked into a patch of stinging nettles. My father grabbed some leaves of dock, which always seem to grow nearby, and rubbed the juice of the leaves on my stings and the itching soon subsided. But stinging nettles have their value too. Grown near the aromatic herbs they are said to increase the aromatic oils in these plants by up to 80 per cent; and like foxglove and lilly-of-the-valley, they improve the keeping quality of plants that they are grown near, particularly tomato.

Other beneficial plants to have around the vegetable garden are wild rose, elderberry, buddleia, privet, golden rod, and mustard.

While companion planting is a lot of fun and makes the vegetable garden more attractive, both to the eye and to the nose, it has a more serious side. It represents an effort on the part of some producers to manage agricultural systems according to principles that can be gained by studying natural systems. The absence of monocultures in nature prompts the question,'''are we directing our effort in the wrong direction by developing technologies to maintain such systems when perhaps we could be developing them to maintain mixed crop systems?"


Gregg, R. B. 1943. Companion and Protective Plants. Bio-Dynamics 3(1), 1-10.

Heckel, A.. (Ed.) 1967. The Pfeiffer Garden Book; Bio-Dynamics in the Home Garden Bio-Dynamic Farming & Gardening Association Inc., Stroudsburg, Penn.

Hylton, William H. (Ed.) 1974. The Rodale Herb Rook. Rodale Press Book Division Emmaus, Pa. 18049

Jeavons, J. 1974. How to Grow More Vegetables Than You Ever Thought Possible on Less Land Than You Can Imagine. Ecology Action of the Midpeninsula 2225 El Camino Real, Palo Alto, California 94306, U.S.A.

Philbrick, H. and Gregg, R. B. 1966. Companion Plants and How to Use Them. The Devin-Adair Co., N.Y.

Tompkins, P. and Bird, C. 1973. The Secret Life of Plants. Avon Books, N.Y.

Copyright 1975 Ecological Agriculture Projects

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