What Is Companion Planting?
Companion planting is the practice of growing different plants in close proximity for mutual benefit. Some plant pairings can deter pests, attract beneficial insects, improve soil health, or simply make the most efficient use of garden space. It's a cornerstone of traditional and organic gardening — and it works.
Understanding which plants make good neighbours — and which ones compete or hinder each other — can meaningfully improve your garden's productivity and reduce the need for chemical interventions.
How Companion Planting Works
Plants influence each other through several mechanisms:
- Scent-based pest confusion: Strong-smelling plants can mask the scent of nearby crops, making them harder for pests to locate
- Trap cropping: Some plants attract pests away from valuable crops
- Nitrogen fixation: Legumes (peas, beans) fix atmospheric nitrogen into the soil, feeding neighbouring plants
- Physical benefits: Tall plants can provide shade or windbreak for smaller, more delicate neighbours
- Attracting beneficial insects: Flowering plants draw pollinators and predatory insects that feed on garden pests
The Three Sisters: A Classic Combination
Perhaps the most celebrated companion planting system is the Three Sisters, developed by Indigenous peoples of North America. It combines:
- Sweetcorn — provides a vertical structure for beans to climb
- Climbing beans — fix nitrogen into the soil, feeding the corn and squash
- Squash or courgette — its large leaves shade the ground, suppressing weeds and retaining moisture
Each plant supports the others — a beautiful example of polyculture in action.
Beneficial Companion Pairings
| Plant | Good Companions | Benefit |
|---|---|---|
| Tomatoes | Basil, marigolds, carrots | Basil may repel aphids; marigolds deter whitefly |
| Carrots | Onions, leeks, rosemary | Alliums and rosemary confuse carrot root fly |
| Brassicas | Nasturtiums, dill, thyme | Nasturtiums act as a aphid trap crop |
| Roses | Garlic, lavender, catmint | Garlic may deter aphids and blackfly |
| Courgette | Nasturtiums, sweetcorn, beans | Ground cover, mutual support |
| Strawberries | Borage, thyme, spinach | Borage deters pests and attracts pollinators |
Plants That Don't Get Along
Just as some plants complement each other, others compete for resources or release chemicals that inhibit neighbouring plants — a process called allelopathy.
| Plant | Avoid Planting Near | Reason |
|---|---|---|
| Fennel | Most vegetables | Releases compounds that inhibit growth in many plants |
| Onions/Garlic | Peas, beans | Can inhibit legume growth |
| Walnut trees | Most garden plants | Releases juglone, which is toxic to many species |
| Brassicas | Strawberries, tomatoes | Competition for nutrients; stunted growth reported |
Flowers That Every Vegetable Garden Needs
Including flowering plants in a vegetable garden is one of the most effective companion planting strategies. These are particularly useful:
- Marigolds (Tagetes): Deter a range of pests including nematodes and whitefly; also attract hoverflies
- Nasturtiums: Lure aphids away from crops; edible flowers and leaves are a bonus
- Borage: Attracts pollinators and predatory insects; said to improve strawberry yields
- Phacelia: An excellent bee plant that also makes a useful green manure
- Sweet alyssum: Low-growing ground cover that attracts hoverflies and parasitic wasps
Getting Started
You don't need to redesign your entire garden to benefit from companion planting. Start small: plant basil next to your tomatoes, or scatter marigolds at the edges of beds. Observe what happens over a season, and gradually incorporate more pairings as your knowledge grows. Your garden — and the wildlife that visits it — will thank you.