Companion Planting: What Works and What Is a Myth

Companion planting means growing certain plants together for mutual benefit, such as pest control, pollination, or better growth. It is a charming idea with a long tradition, but the claims range from well supported to little more than gardening folklore. Knowing the difference saves you time and disappointment.

Ideas with reasonable support

• Flowers for beneficial insects. Planting flowers such as alyssum, calendula, and dill near vegetables can attract pollinators and insects that feed on pests.
• Trap crops. A sacrificial plant, such as nasturtium for some aphids, can draw pests away from your main crop, though results vary.
• Tall plants giving shade. Tall crops can provide light shade to heat-sensitive plants like lettuce in summer.
• Three Sisters. Corn, climbing beans, and squash is a traditional combination in which the corn supports the beans and the squash leaves shade the soil.

Ideas with mixed or limited evidence

Marigolds are famous for pest control. Some French marigold varieties can suppress certain root nematodes in the soil under the right conditions, but the claim that marigolds protect an entire bed from all pests is overstated. Basil near tomatoes is often recommended for flavour and pest control, but the evidence is thin. It is still a pleasant pairing in the kitchen.

What the research says in general

Studies of mixed planting, also called intercropping, show benefits in some systems, such as reduced pest pressure, and no effect in others. Results depend heavily on the crops, the pests, and the climate. There is no single list of friends and enemies that works everywhere.

A practical approach

• Try one or two pairings at a time and keep notes.
• Do not rely on companions instead of good basics such as sun, water, and soil.
• Give each plant enough space. Crowding causes more problems than it solves.
• Mix flowers and herbs into the vegetable bed. It looks good and helps pollinators.

Companion planting is worth a try, as long as you treat it as an experiment instead of a guarantee.