Companion planting: what actually works

Some plants genuinely grow better when they're near each other. Others get in each other's way. Knowing which is which — and why — can save you a few headaches and help your plants along.

What companion planting actually is

Companion planting is the practice of growing two or more species near each other in a way that benefits at least one of them. The real benefits come from a small number of mechanisms:

Pest confusion and deterrence. Some plants release strong-smelling natural chemicals from their leaves or stems that mask the scent of a neighbour, making it harder for specialist pests to find their target.

Trap cropping. Some plants are so attractive to a particular pest that the pest ignores everything else and heads for the trap. You sacrifice it and save the main crop.

Beneficial insect habitat. Flowering herbs and marigolds attract hoverflies, ladybugs, lacewings, and parasitic wasps — all of which eat aphids and caterpillars for a living.

Physical cooperation. Some plants simply complement each other physically, or improve the microclimate for their neighbour. Tall, sturdy crops can act as a natural climbing support or cast useful shade, while low, ground-covering plants keep moisture in the soil and suppress weeds.

Avoiding antagonism. Some plants simply don't belong near each other — they compete for the same nutrients, share diseases, or produce root chemistry that suppresses neighbours. Knowing the bad pairings matters as much as knowing the good ones.

All of these mechanisms are real. They're also specific — a pairing that helps one crop won't automatically help another. This is why generic charts that list "good" and "bad" neighbours often contradict each other.

The pairings that earn their reputation

The pairings below are the ones that come up consistently across multiple independent sources — the RHS, Burpee, and Louise Riotte's classic Carrots Love Tomatoes — and where the mechanism behind the claim is plausible.

Tomato and basil. A genuinely good pair. Basil's scent appears to confuse some of tomato's insect pests (whiteflies in particular), and in a small kitchen garden they're also a natural culinary pair. Plant a basil seedling at the base of each tomato.

Tomato with borage, nasturtium, and marigold. Tomato is one of the crops companion planting was made for. Borage attracts pollinators and may deter tomato hornworm. Nasturtium is a hoverfly magnet and an aphid trap crop. Marigold releases substances from its roots (called root exudates) that suppress certain nematodes — tiny worms in the soil that can damage plant roots. All three come up in multiple sources with plausible mechanisms.

Carrot and spring onion. The onion family's strong scent is thought to confuse carrot root fly, while carrots may return the favour for onion fly. Practical and worth doing if you grow both.

Strawberry and borage. One of the oldest pairings in the books, endorsed by RHS, Burpee, and Riotte alike. Borage pulls in pollinators during strawberry flowering and is said to improve flavour and yield.

Courgette with corn and beans — the Three Sisters. Indigenous to the Americas and perhaps the most famous companion arrangement in the world. Real, effective, well-documented. If you have the space, try it: corn supports the beans, beans feed the corn, squash smothers weeds at their feet.

Cabbage family (brassicas) with thyme and sage. Cabbages, broccoli, kale, and their relatives attract cabbage white butterflies from miles around. Strong-smelling woody herbs around the edge of the bed seem to confuse the butterflies' search. Not a complete defence — you'll still want netting — but a useful extra layer.

The pairings to avoid

Some plants are genuinely bad neighbours. These come up across every serious source:

Tomato near potato, the cabbage family, or fennel. Tomato and potato share blight. Cabbages and tomatoes don't seem to do each other any favours. Fennel releases chemicals from its roots that actively suppress most nearby crops — fennel really is the loner of the vegetable garden.

Onion family near peas or beans. The onion family (garlic, onions, leeks, chives) appears to inhibit the nitrogen-fixing bacteria on the roots of legumes — the plant family that includes peas and beans. These bacteria pull nitrogen from the air and feed it to the plant, so disrupting them means your beans and peas get less of the free fertiliser they rely on. Keep the two families apart.

Strawberry near the cabbage family. Every source agrees that strawberries and cabbages bring out the worst in each other, even if the mechanism isn't fully understood.

Online charts list many more antagonisms, but most show up in only one source with thin reasoning behind them. The three above are the ones to plan around.

The honest conclusion

You don't need to memorise a chart. A simple rule to start with: grow basil next to your tomatoes, grow onions next to your carrots, and keep your onions and garlic away from your peas and beans. That alone gives you most of the benefit available.

The Ortaia app suggests companion planting pairings for each crop, so you can check what grows well together as you plan your beds. Beyond that, a few seasons of trying things and watching what happens will teach you more than any list can.

Plan your first beds with Ortaia

That's the foundations bundle. From here, the next step is putting it into practice — picking your beds, choosing your crops, and getting timing reminders that fit your local climate. The Ortaia app handles all of that.

Try the Ortaia app →

Further reading

Louise Riotte — Carrots Love Tomatoes: Secrets of Companion Planting for Successful Gardening (Storey Publishing, revised edition 1998). The classic English-language reference. Some claims are folklore, many are accurate — worth reading critically.

Royal Horticultural Society — Companion planting

Burpee — Companion planting guide

Jessica Walliser — Plant Partners: Science-Based Companion Planting Strategies for the Vegetable Garden (Storey, 2020). The most rigorous recent treatment of which pairings actually hold up under research.