The Beginner's Guide to Companion Planting
By Emily Hart
Published June 28, 2026 · Updated September 23, 2026
Companion planting means growing plants near each other because the combination helps: pests are confused or distracted, beneficial insects move in, space and light are used more efficiently, or one plant supports another. Some pairings rest on well-understood ecology; others are traditional garden wisdom with thinner evidence. Knowing the difference helps you plan a bed that actually works instead of following a chart blindly.
Quick answer: Start with pairings that have a clear mechanism: tall crops shading lettuce, fast radishes between slow crops, beans and corn sharing space, flowers like alyssum, dill and calendula drawing in predatory insects, and nasturtiums as trap crops for aphids. Group plants by sun and water needs first, give each its mature spread, keep potatoes and tomatoes apart to limit shared disease, and rotate crop families every year.
How Companion Planting Works
| Mechanism | How it helps | Examples |
|---|---|---|
| Habitat for beneficial insects | Flowers feed predators and parasitic wasps that eat pests | Sweet alyssum, dill, fennel (in its own spot), yarrow, calendula |
| Trap cropping | A plant pests prefer draws them away from the main crop | Nasturtiums for aphids, radishes for flea beetles |
| Masking or confusion | Strong scents and mixed plantings make crops harder for pests to find | Onions or garlic near carrots |
| Physical support and shade | Tall plants support climbers or shade heat-sensitive crops | Corn for pole beans; tomatoes shading lettuce |
| Efficient use of space and time | Fast and slow crops share a bed | Radishes or lettuce between tomatoes or peppers |
| Soil benefits | Legumes host nitrogen-fixing bacteria; diverse roots improve soil | Beans and peas, especially when plant residue is returned to the soil |
How Strong Is the Evidence?
| Pairing | Evidence | Notes |
|---|---|---|
| Flowering plants for beneficial insects | Good | Well supported by research on insect habitat |
| Trap crops like nasturtiums | Moderate | Works when trap plants are monitored and pests removed |
| Three Sisters (corn, beans, squash) | Good for space use | A traditional Indigenous system; best with suitable varieties and spacing |
| Onions deterring carrot fly | Mixed | Some effect in close interplanting; row covers are more reliable |
| Marigolds and nematodes | Moderate for specific types | French marigolds grown as a dense cover crop help most; a few plants have little effect |
| Basil improving tomato flavor | Weak | Mostly tradition, but basil does no harm |
Classic Combinations Worth Trying
Tomatoes + basil + marigolds. A popular, easy trio. The flowers attract pollinators and beneficial insects, and basil fits beneath tomatoes. Don’t expect it to stop pests alone.
Carrots + onions or leeks. Alternating rows may make carrots harder for carrot flies to find. A fine insect mesh cover is the dependable backup.
Corn + beans + squash (Three Sisters). Corn supports pole beans, squash leaves shade the soil and suppress weeds, and beans add diversity. Plant corn first so it’s tall enough before beans climb, and give the planting plenty of room.
Lettuce + tall crops. Lettuce planted on the shady side of tomatoes, trellised cucumbers or corn stays cooler and bolts later in summer.
Radishes + slow crops. Radishes mature in weeks and are harvested before carrots, squash or cucumbers need the space.
Nasturtiums as a trap crop. Aphids often prefer them over nearby vegetables. Check them regularly and remove heavily infested stems.
Flower strips for beneficial insects. A border of alyssum, calendula, cosmos or yarrow brings in hoverflies, lacewings and parasitic wasps.
Combinations to Avoid
| Avoid | Why |
|---|---|
| Potatoes near tomatoes | Same family; share late blight and other diseases |
| Beans or peas next to onions and garlic | Traditional advice that alliums slow legume growth; spacing them apart is easy |
| Fennel in a mixed bed | Grows large and competes; plant it separately |
| Tomatoes next to corn | Both host the corn earworm (tomato fruitworm) |
| Squash crowding low crops | Big leaves shade out small plants by midsummer |
| Mint in open beds | Spreads aggressively; grow in containers |
| Brassicas planted in the same spot every year | Builds up pests and clubroot; rotate |
Dill and carrots are in the same family and can attract some of the same pests, so many gardeners keep mature dill a short distance from carrots. Young dill near carrots is generally fine.
Quick-Reference Chart
| Plant | Good companions | Keep apart from |
|---|---|---|
| Tomatoes | Basil, marigolds, lettuce, carrots, onions | Potatoes, corn, fennel |
| Carrots | Onions, leeks, lettuce, radishes, rosemary | Mature dill, parsnips |
| Cucumbers | Beans, radishes, dill, nasturtiums | Potatoes |
| Peppers | Basil, onions, spinach, carrots | Fennel |
| Beans | Corn, squash, cucumbers, carrots | Onions, garlic, chives |
| Squash | Corn, beans, radishes, nasturtiums | Potatoes |
| Onions and garlic | Carrots, beets, lettuce, tomatoes | Beans, peas |
| Lettuce | Carrots, radishes, taller crops for shade | Very aggressive spreaders |
| Potatoes | Beans, corn, cabbage | Tomatoes, squash |
Treat this as a starting point. Local conditions, varieties and pests matter more than any universal chart.
Plan Your Layout
- Sketch the bed and note sun, shade and water access.
- Group by needs first: plants sharing sun and water needs go together; chart pairings come second.
- Allow for mature size. Check spacing on the seed packet, not seedling size.
- Layer in quick crops like radishes, lettuce and spinach between slow ones.
- Add flowers at bed ends or along edges for beneficial insects.
- Rotate crop families each year: tomatoes and potatoes, brassicas, legumes, alliums, squash and cucumbers. Raised beds make rotation easy to track.
- Keep notes or photos of what grew where.
Containers and Small Spaces
The same principles apply in pots, but space is tight. Pair a main crop with a small companion, such as a tomato with basil or a pepper with a few marigolds. Avoid putting two vigorous plants in one container. See our guide to growing tomatoes in pots for container sizes.
Other Ways to Reduce Pests
Companion planting works best alongside other good practices: healthy soil with compost, correct soil pH, crop rotation, row covers during peak pest periods, and regular checks so problems are caught early.
FAQ
Does companion planting really work?
Some pairings have good support, especially flowers for beneficial insects and smart use of space. Others are more tradition than science. It’s a helpful tool, not a guarantee.
What’s the best companion for tomatoes?
Basil and flowers like marigolds or alyssum are easy, popular companions. Keep potatoes and corn away.
Can I plant garlic next to tomatoes?
Yes, many gardeners do. Just keep garlic and onions away from beans and peas. See our guide to planting garlic in fall.
Do marigolds keep pests away?
They attract beneficial insects and pollinators. Their effect on soil nematodes comes mainly from dense plantings of certain French marigold varieties, not from a few plants scattered around.
