Companion planting

Introduction to companion planting

The principle of companion planting is that growing specific combinations of plants together brings mutual benefits in health and vigour, and a consequent reduction in pest and disease problems. As yet, there is no scientific explanation for these effects. A series of experiments was started in 1997 at Wisley, to assess the possible benefits for gardeners. The early results were promising, but they were not confirmed by later experiments.

It is believed that companion plants work in a number of ways.

• They can produce chemicals which repel pests, or mask their scent from pests. French and African marigolds (Tagetes) reduce nematodes, slugs and wireworms in crops such as tomatoes. The effect is associated with the production of root exudates which appear to deter pest attack. This is supported by experiments at the Henry Doubleday Research Association (HDRA). Onions planted between rows of carrots may help to reduce attack by carrot flies.
• Their physical presence may camouflage the shape of the crop, or act as a barrier to the crop.
• Trap crops attract insects away from the main crop. Chinese cabbage which has gone to seed can be used to attract aphids away from other cabbage plants nearby.

Work at Wisley

An introductory article appeared in The Garden .
Jackson, A & Parsons, D. 1998, May. Good neighbours. The Garden (RHS) 123(5): 340-343. A review of the subject and discussion of the results of some recent experiments at Wisley .

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