Companion planting is the practice of designing plant combinations that benefit each other in various ways: deterring pests, attracting beneficial insects, improving soil health, or supporting growth through physical means. In the medicinal herb garden, the relationships between plants are layered and interesting in ways that go beyond pure practicality.
The Foundational Partners
Calendula is one of the most broadly beneficial companion plants in any garden. It attracts an extraordinary range of beneficial insects, including hoverflies, lacewings, and parasitic wasps, whose larvae are significant predators of aphids and other common pests. It also has some evidence of allelopathic activity against certain soil nematodes that can harm root crops. Plant calendula liberally throughout the medicinal bed and you create a more balanced and self-regulating ecosystem.
Borage (Borago officinalis) is another widely beneficial companion, particularly attractive to bumblebees due to its star-shaped blue flowers and their accessible nectar. It self-seeds prolifically once established, creating a colony that pollinators use throughout the season. It is also medicinally useful in its own right, with a long tradition as an adrenal-supportive herb (its old name was “courage herb”) and lovely edible flowers for salads and garnish.
Beneficial Combinations
Chamomile growing among brassicas (if your medicinal garden includes any food crops) is a traditional pairing: chamomile is believed to deter some brassica pests and to improve the growth of nearby plants through root exudates. Lavender planted at the edges of herb beds deters some pests through its strong fragrance and attracts pollinators. Yarrow at the border of any bed attracts predatory insects and has allelopathic properties that may support the health of neighboring plants.
Plants That Need Space
Some medicinal herbs are not good companions because they are too dominant. Mint spreads aggressively and should be contained. Horseradish, once established, is extremely difficult to remove. Comfrey is so vigorous that it can overwhelm nearby plants unless given plenty of space or repeatedly cut back. Know which plants need management before planting.
The Herbalist Codex app has growing notes for individual herbs that include companion planting recommendations and any allelopathic or competitive behavior to be aware of before placing them in your garden design.