Companion planting is the practice of growing vegetables together that help each other — and keeping apart the combinations that harm each other. Some pairings are well supported: carrots and onions genuinely help each other, because onion smell confuses carrot rust fly and carrot smell confuses onion fly. Some are traditional and widely used, such as the three sisters — corn, beans and squash grown together. And some are folk claims that sound good but have little evidence behind them, so this guide marks the difference clearly. The timings below use published ranges for common vegetables, which vary by variety, climate and soil. As with everything in this guide, check your local extension service for advice suited to your area.
The honest truth about companion planting is that it helps at the margins. Good spacing, good soil, proper watering and crop rotation matter far more than which vegetables sit next to each other. Companion planting will not save a crowded, underwatered bed, and it will not replace rotation. But used well, it makes a good garden slightly better: it confuses pests, attracts pollinators and predators, uses space more efficiently, and makes the garden more interesting to grow and to look at. Think of it as the finishing touch, not the foundation.
The best vegetable companions
| Pairing | Why it works | How to plant it |
|---|---|---|
| Carrots + onions | Onion smell confuses carrot rust fly; carrot smell confuses onion fly | Alternate rows or interplant in the same row |
| Tomatoes + basil | Basil attracts pollinators and may confuse some pests; uses space well | Plant basil around the base of tomato plants |
| Lettuce + tomatoes | Lettuce uses the shade under tomatoes; tomatoes use the space above | Sow lettuce around tomato plants in summer |
| Beans + sweet corn | Beans climb the corn; beans fix nitrogen that corn uses | Plant corn in a block, beans at the base once corn is knee-high |
| Cabbage + dill | Dill attracts beneficial insects that eat cabbage pests | Plant dill at the edge of the brassica bed |
| Cucumbers + radishes | Radishes may deter cucumber beetles; fast crop harvested before cucumbers spread | Sow radishes around cucumber plants |
| Potatoes + beans | Beans fix nitrogen; potatoes use the space below | Plant beans at the edge of the potato bed |
| Spinach + peas | Peas fix nitrogen; spinach uses the shade | Sow spinach under and around pea plants |
| Marigolds + almost anything | Marigolds attract pollinators and may deter some soil pests | Plant marigolds at the ends of rows and around bed edges |
| Nasturtiums + brassicas | Nasturtiums act as a trap crop for aphids and cabbage white | Plant nasturtiums at the edge of the brassica bed |
Carrots and onions are the best-supported pairing in the vegetable garden: each one's smell confuses the other's main pest, and they grow well together because onions are shallow-rooted and carrots are deep-rooted, so they do not compete for the same soil. Tomatoes and basil are the most popular pairing, and while the flavour claims made for it are folk wisdom rather than proven fact, basil does attract pollinators, uses the space at the base of the tomato plant well, and is a crop you will actually eat. Lettuce under tomatoes is pure space efficiency: the tomato shades the lettuce in summer heat, and the lettuce keeps the soil cool and moist. The companion planting finder helps you check any combination, and the growing guides for tomatoes, carrots and cabbage cover the individual vegetables in detail.
The three sisters: corn, beans and squash
The three sisters is a traditional planting system in which sweet corn, climbing beans and squash are grown together in the same bed. Corn provides a living pole for the beans to climb. Beans fix nitrogen from the air, feeding the hungry corn. Squash spreads across the ground, shading the soil, holding moisture in and suppressing weeds. It is an elegant system, and it works — with conditions. Corn needs a block, not a single row, for pollination, so plant at least four rows of corn in a block. Beans should be sown once the corn is knee-high, so the corn is strong enough to support them. Squash needs 36–48 inches of space and will sprawl across the bed, so give the whole planting plenty of room.
The three sisters suit a large bed and a warm climate, and they are a good example of companion planting as a system rather than a single pairing. They do not suit a small garden, because corn at 12–15 inches spacing in a block, beans climbing it, and squash sprawling around it take up a lot of room — and the corn shades everything else. If you have the space, try it on one bed and compare it with the same vegetables grown separately. Keep notes, and judge by your own results rather than by tradition alone.
Bad neighbours: combinations to avoid
| Combination | Why to avoid it |
|---|---|
| Onions + beans or peas | Onions are traditionally said to stunt beans and peas; keep them apart |
| Tomatoes + sweet corn | They share the corn earworm, which attacks both |
| Potatoes + tomatoes | Both are nightshades and share blight and other diseases |
| Cabbage + tomatoes | They compete and are traditionally said to stunt each other |
| Fennel + almost anything | Fennel is traditionally said to inhibit most vegetables; grow it alone |
| Beans + garlic or onions | Alliums are traditionally said to stunt beans |
| Cucumbers + potatoes | They compete for space and water, and potatoes may spread disease |
The most important bad neighbours are the ones that share diseases: potatoes and tomatoes are both nightshades and share early blight and late blight, so they must not grow together or follow each other in the same bed. Tomatoes and sweet corn share the corn earworm, which eats corn tips and bores into tomato fruit. Onions and beans are a traditional bad pairing — onions are said to stunt beans and peas — and while the evidence is not strong, there is no reason to risk it when there are so many good pairings available. Fennel is the one plant to grow on its own: it is traditionally said to inhibit the growth of most vegetables nearby, so give it a corner to itself. The vegetables pest control guide and the vegetables disease prevention guide explain why disease-sharing combinations matter so much, and the tomatoes companion plants guide covers tomato pairings in detail.
Flowers and herbs as companions
Flowers and herbs earn their place in the vegetable garden by attracting pollinators and predators. Marigolds are the classic vegetable-garden flower: they attract hoverflies and other beneficial insects, and they are traditionally said to deter some soil pests. Calendula does the same job and is easier to grow. Dill and fennel attract lacewings and parasitic wasps that eat aphids and caterpillars — though fennel should be grown at the edge, away from other vegetables, as noted above. Basil attracts pollinators to tomatoes and peppers. Borage attracts bees to strawberries and squash, and is traditionally said to improve the flavour of nearby vegetables, though that claim is folk wisdom rather than proven fact.
Nasturtiums deserve a special mention: they act as a trap crop for aphids and cabbage white butterflies, drawing pests away from brassicas and beans. Plant them at the edge of the bed, check them regularly, and remove them if they become heavily infested — a trap crop that is left to breed pests becomes a source of pests, not a solution. The growing guide for calendula covers one of the best companion flowers, and the nasturtiums companion plants guide covers nasturtiums specifically.
Planning a mixed bed
Plan mixed beds around height, root depth and timing, not just companionship. Tall vegetables — sweet corn, climbing beans, tomatoes — go on the north side of the bed so they do not shade shorter plants. Shallow-rooted vegetables — lettuce, onions, radishes — pair well with deep-rooted ones — carrots, tomatoes, parsnips — because they use different layers of soil. Fast vegetables — radishes at 25–40 days, lettuce at 45–60 days — can be sown between slow vegetables — tomatoes at 60–85 days, onions at 90–120 days — and harvested before the slow crop needs the space.
A simple mixed bed might hold two tomato plants at 24–36 inches apart, basil around their bases, lettuce sown between them for an early crop, and marigolds at the ends of the rows. Another might hold a block of carrots interplanted with onions, with radishes sown in the gaps for a fast first harvest. Keep the spacing right — companionship never justifies crowding — and rotate families every year, since companion planting does not replace rotation. The plant spacing calculator helps you fit combinations into your beds, and the vegetables spacing guide gives the spacing for each vegetable.
Common companion planting mistakes
- Treating companion planting as a substitute for spacing, rotation and good soil — it is not.
- Believing every folk claim, including the ones with no evidence behind them.
- Crowding plants because they are "companions", so air cannot move and disease spreads.
- Planting fennel in the middle of the vegetable bed.
- Growing potatoes and tomatoes together, so blight spreads between them.
- Planting a trap crop such as nasturtiums and then leaving it to breed pests.
- Never keeping notes, so you cannot tell which pairings actually helped.
- Planting sweet corn in a single row instead of a block, so pollination fails.
Most companion planting mistakes come from treating it as magic rather than method. Use the pairings with real evidence behind them, keep the spacing right, rotate every year, and keep notes on what worked. That is the whole method.
Frequently asked questions
What grows well with tomatoes?
Basil, lettuce, marigolds and carrots are all good tomato companions. Avoid potatoes and sweet corn, which share diseases and pests with tomatoes.
What is the three sisters planting method?
A traditional system of sweet corn, climbing beans and squash grown together: corn supports the beans, beans fix nitrogen for the corn, and squash shades the soil. It needs a large bed and a warm climate.
Do carrots and onions really help each other?
Yes — this is one of the best-supported pairings. Onion smell confuses carrot rust fly and carrot smell confuses onion fly, and their roots use different soil depths.
What should not be planted next to beans?
Onions and garlic are traditionally said to stunt beans, so keep alliums away from bean and pea beds.
Does companion planting really work?
Some pairings have real evidence behind them, such as carrots and onions. Others are folk claims with little proof. Use the proven pairings, keep good spacing and rotation, and judge by your own results — check your local extension service for advice in your area.
Related guides
For more vegetable help, browse the guides hub and the growing guides hub, and try the companion planting finder and the plant spacing calculator. Good next reads are the vegetables pest control guide, the vegetables spacing guide, and the growing guide for tomatoes. And as always, check your local extension service — local advice beats any general guide for your soil, your weather and your varieties.