Gardeners have known for centuries that some plants grow better when certain other plants are growing nearby. Science has determined some of the basis for this, but many successful plant combinations still have no explanation. The practice of purposely placing two plants in close proximity for the benefit of one or both of them is called companion planting.
The classic companion planting combination is known as the Three Sisters. In the Native American tradition, corn, beans and squash are planted together. The corn grows tall and serves as a support for the beans. The beans in turn, fix nitrogen in the soil, important for nitrogen loving, heavy feeding corn. The squash surrounds the other two, covering the ground to hold in moisture and prevent weeds, and the prickles on the squash aid as a repellant to scavenging raccoons and other predators.
Sometimes a neighboring crop is a natural means of pest control in that it is more attractive to pests than the main crop and distracts them from it. For example, dill planted near tomatoes draws off tomato hornworms.
Other plants provide pest control by exuding chemicals from their roots or aerial parts. Herbs are especially good at this. Basil repels flies and mosquitoes and catnip repels flea beetles. Garlic deters Japanese beetles, so would be ideal near roses. Horseradish deters potato bugs, and French and African marigolds discourage Mexican bean beetles, nematodes and other bean pests. Nasturtiums discourage aphids, squash bugs, and striped cucumber beetles. Thyme repels cabbage worms.
Another way plants help each other is by attracting pollinators and other beneficial insects. My vegetable garden is a patchwork of flowers and vegetables. The flowers attract pollinating insects which then visit the vegetable crops and pollinate them. Beneficial insects are those that are predators to pest insects. Predator insects include ladybird beetles, lacewings, hover flies, assassin bugs and robber flies. Dill, coriander, dandelions, fennel, cosmos, tansy, lemon balm, spearmint, bugleweed, yarrow, and Queen Anne’s lace are just a few plants that attract beneficial insects.
Sometimes plants help others by providing a wind break or shade. Corn on the west side of tomatoes prevents hot summer winds from desiccating the tomato plants, while corn on the south side of a late lettuce crop provides cool shade so the lettuce doesn’t bolt.
Many vegetable and herb gardening books include charts listing good and not-so-good plant companions. You could make yourself crazy trying to lay out your garden according to the charts. I have found them more useful for learning what crops are incompatible than for those that are well-suited. There are just too many good combinations. I use the compatible columns of the charts, instead, as inspiration for ideas for new plants to grow next to old favorites to enhance their growth.
Leave a Reply