What Is Companion Planting?
Companion planting is the practice of growing different plants in close proximity so that they benefit one another. It's one of the oldest techniques in organic growing — part science, part accumulated folk wisdom — and when done thoughtfully, it can make a real difference in the health and productivity of a kitchen garden.
The benefits can include natural pest deterrence, improved pollination, better use of space, and enhanced soil fertility. Not every claimed pairing is backed by rigorous science, but many are, and trial-and-observation in your own garden is part of the pleasure.
How Companion Planting Works
Plants interact with their neighbours in several ways:
- Chemical signalling – Some plants release compounds from roots or leaves that repel insects, attract beneficial predators, or inhibit the growth of competing plants.
- Physical interaction – Tall plants can shade low-growing companions that prefer cooler conditions. Dense groundcover plants can suppress weeds that would otherwise compete with taller crops.
- Attracting beneficial insects – Flowering herbs and wildflowers attract hoverflies, parasitic wasps, and other predatory insects that feed on pest species like aphids.
- Nitrogen fixation – Legumes (peas, beans, clover) fix atmospheric nitrogen in root nodules, making it available to neighbouring plants.
Classic Companion Planting Combinations
The Three Sisters
Perhaps the most famous companion planting system, originating with Indigenous North American agriculture. The three crops — corn, beans, and squash — are planted together in a mutually supporting guild. Corn provides a climbing structure for beans; beans fix nitrogen that feeds the corn and squash; squash leaves spread across the ground, shading out weeds and retaining soil moisture.
Tomatoes and Basil
A beloved combination in kitchen gardens. Basil is said to repel aphids and whitefly while attracting pollinators. Whether or not it genuinely improves tomato flavour (as some claim) is debated, but the practical pest-deterrence properties are widely observed. It certainly makes efficient use of bed space.
Carrots and Onions
Carrot root fly and onion fly are both pests that locate their hosts by scent. Interplanting carrots and onions (or leeks) is thought to confuse both pests — the scent of each crop masking that of the other. Results vary, but it's a logical and space-efficient combination.
Brassicas and Nasturtiums
Nasturtiums are excellent trap crops for aphids — they attract aphids away from your brassicas, and in turn attract predatory insects that feed on those aphids. They also act as a sacrificial host for cabbage white butterfly eggs in some gardens, drawing egg-laying away from your crops.
Companion Planting Quick Reference
| Crop | Good Companions | Poor Companions |
|---|---|---|
| Tomatoes | Basil, marigolds, carrots, parsley | Fennel, brassicas, corn |
| Carrots | Onions, leeks, rosemary, sage | Dill, parsnips |
| Beans | Squash, corn, strawberries | Onion family, fennel |
| Brassicas | Nasturtiums, dill, celery, onions | Strawberries, tomatoes |
| Courgette/Squash | Corn, beans, nasturtiums, borage | Potatoes |
| Lettuce | Carrots, radishes, tall flowers for shade | Celery, parsley |
The Role of Flowers in a Vegetable Garden
Integrating flowering plants throughout a vegetable garden is one of the most impactful things you can do for its overall health. Marigolds (especially Tagetes species) are particularly well studied — their root exudates deter certain soil nematodes, and their strong scent is thought to confuse or repel a range of flying insect pests. Borage attracts bumblebees and is thought to benefit strawberries and tomatoes nearby. Phacelia, calendula, and sweet alyssum are all excellent for attracting beneficial insects.
Learning From Your Own Garden
Companion planting isn't a fixed formula — it's a set of principles and observations to experiment with. Keep a simple garden journal noting what grows near what and how each combination performs. Over seasons, you'll develop an understanding of what works in your specific conditions, climate, and soil. That localised knowledge is ultimately more useful than any general guide.