Herbs Make Good Plant Partners and Companions

Companion planting is the concept of growing plants near each other so that one plant provides a known benefit to the other. In the past, many claims about companion planting were only anecdotal. The following provides research-based information that the gardener can now rely upon scientifically.

Research shows that several herbs have documented roles as plant partners in vegetable gardens. In general, creating a rich, diverse habitat, a polyculture, that includes many species, helps limit outbreaks of undesirable pests and does so in a more environmentally friendly way than using pesticides. Polycultures, on the whole, make it harder for insects to find a specific plant. Interplanting specific vegetables with specific herbs suppresses pest populations in several ways.

Pests, in general, find plants by using physical cues (like seeing the plant) or chemical cues (touching down and "sampling" the plant). Herbs can visually confuse certain pests and limit their landings on target vegetables. Many herbs can disrupt pests' feeding behaviors by "masking" the volatile chemicals of the target vegetable with their own. Herbs don't repel insect pests but rather confuse them. Interplant basil with tomatoes, and the basil will help mask the tomato plants from thrips.

Herbs can also interfere with pest egg-laying behaviors, thereby reducing their numbers in the next generation. Surrounding tomatoes with basil has been shown to reduce egg-laying behavior in adult tomato hornworms.

Herbs can also physically impede the movement of pests toward a crop or toward areas near the crop where they may lay eggs. By underplanting tomato plants with thyme, the herb forms a mulch-like carpet that deters egg-laying by yellow-striped armyworm moths.

In some cases, the volatile oils of an herb attract beneficial insects that eat the pests. Herbs may also provide pollen or nectar to these beneficials. Calendula attracts many beneficial insect species that feed on aphids. Planting calendula near collards has been proven to deter aphids. Plant cilantro, dill, or fennel to encourage the presence of many different species of aphid-eating beneficial insects, including lacewings, ladybugs, parasitic wasps, spiders, and syrphid flies. Plant these herbs near greens and lettuce to reduce aphid populations and the damage they cause.

Herbs also increase pollination of many vegetable and fruit crops by drawing in certain pollinators to the garden. If allowed to bloom, the flowers of rosemary, oregano, basil, and thyme will attract various species of sweat bees. These native bees will go on to pollinate many nearby crops.

While this article focuses on herbs as companion plants for vegetables, many other plants can be partners to vegetables, including other vegetables. For further research-based information, please read Plant Partners: Science-Based Strategies for the Vegetable Garden by Jessica Walliser (Cool Springs Press, 2020).