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Use companion planting on the evidence

Companion planting is widely promoted, but only some effects are supported by research. Use it for the mechanisms that work, and do not rely on it to replace pest management or fertility.

How

1. Use physical benefits that are supported: tall plants as windbreaks or shade, ground covers to cool soil and hold moisture, sturdy plants to support climbers (WSU Extension).
2. Plant diverse flowering plants to support predators and parasitoids of pests; WSU describes this as making biological control more likely, not guaranteed.
3. Use dense ground covers or living mulches to suppress weeds.
4. Do not rely on aromatic herbs such as mint to repel pests: WSU reports that field studies do not support lab results because the scent disperses too quickly.
5. Treat claims that the Three Sisters (corn, beans, squash) give more food with less water as unproven; WSU found some field studies reported lower bean and squash yields in the mix.
6. Remember companions also compete for light, water and nutrients. Give them space and water as for any crop.

Sources

1. Gardening with Companion Plants (Home Garden Series). Washington State University Extension, accessed 2026-11

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