Knowing what grows well with onions and what doesn't can help produce not just a better harvest, but healthier soil and a healthier garden. Here's an overview of onion companion planting options for attracting beneficial insects, repelling pests, improving pollination, and maximizing your garden space.
Skip Ahead: Benefits of Companion Planting • The Best Companion Plants for Onions • Bad Companions for Onions • Onion Pests
Benefits of companion planting with onions
As companion plants, onions can deter pests, improve soil quality, maximize planting space, and enhance yields of nearby plants.
Generally, their strong scent makes onion family plants fantastic companions for vulnerable vegetables from other families, such as carrots, beets, and kale. This is because, like garlic and chives, onions mask the scent of nearby crops by releasing volatile organic compounds that confuse pests. This can help reduce damage from pests like aphids, cabbage loopers, and diamondback moths.
As a root vegetable, growing onions can also maximize your planting space. Grown with companions like leafy greens, fruiting veg, or herbs, onions take up little extra space. Onion companions also benefit from improved soil quality, thanks to onions' surprisingly long feeder roots.
The best companion plants for onions
Most of the best companion plants for onions will benefit from the alliums' strong scent, but some are also thought to improve onion flavor and yields. Generally, what grows well with onions are root crops, brassicas, catch crops, and cool-weather herbs-- but those aren't your only options.
Here are some good companion plants for onions and onion family plants:
- Brassicas (kale, cabbage, broccoli, cauliflower, bok choy)
- Tomatoes
- Peppers
- Potatoes
- Lettuce
- Radish
- Beets
- Carrots
- Dill
- Parsley
- Cilantro
- Basil
- Chamomile
- Marigolds
- Nasturtium
- Yarrow
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Vegetable companions
Generally, the best vegetables to plant next to onions are ones that share its soil and water requirements and will benefit from its pest-deterring qualities. This includes some root vegetables, fruiting vegetables, and most brassicas.
Here's what to plant next to onions for a healthy harvest:
- Brassicas
- Tomatoes
- Peppers
- Potatoes
- Lettuce
- Radish
- Beets
- Carrots
Planting brassicas like kale, broccoli, and cabbage with onions, garlic, or chives is a classic companion planting combo and one of the best ways to protect them from common pests. For years, research has shown that onions and onion family plants can deter brassica pests like whitefly, cabbage loopers, cabbage moths, and cabbage aphids.
Companion planting onions with tomatoes, basil, and marigolds makes for healthy plants resilient to pest damage. The basil and marigolds will shade the soil at the base of the tomatoes, and all three companion plants will help to ward off pests. Just be sure to give each plant adequate space, and plant the onions and basil in full sun.
Peppers planted with onions create a nice defense against a wide range of pests, and both vegetables will enjoy similar conditions.
Potatoes need full sun, rich soil, and regular mounding up, so planting onions and potatoes together in side-by-side drills makes sense. The potatoes may benefit from onions deterring pests like potato beetles, and the onions will enjoy potatoes' well tilled soil.
Lettuces and radishes planted with onions function as row markers and grow as catch crops, maturing before the onions' leaves start to die back. Onions and onion family plants may also help protect lettuces from aphids and other common pests.
Onions and beets also grow well together; there is some evidence that onions can repel the flea beetles that prey on beets.
Finally, companion planting with carrots can maximize your growing space, as carrots' deep taproots won't compete with onions for nutrients. Onions also mask carrots' scent, protecting them from carrot fly.
Herb companions
- Dill
- Parsley
- Cilantro
- Mint
- Basil
- Chamomile
Companion planting cilantro with onions can help protect cilantro from pest damage by masking the herb's scent. This applies to other other carrot family herbs; for the same reasons, onions are a good companion plant for parsley and dill, as well.
Mint and basil are both fragrant herbs that attract pollinators. Planted with onions, green onions, or chives, they can create a sort of aromatic defense against pests.
Chamomile planted with onions is thought the encourage the alliums' growth and bring balance to pest problems through their strong scents. German chamomile is an annual, while Roman chamomile is a perennial hardy down to zone 3. Both types want full sun, free draining soil, and can tolerate onions' water requirements. They're also low growing, so they can act as a living mulch around onions.
Flower companions
- Marigolds
- Nasturtium
- Yarrow
Marigolds suppress nematode populations in the soil, while nasturtium can act as a trap crop for nematodes and aphids. Both flowers are fantastic companion plants for onions, tomatoes, peppers, and other vegetables susceptible to nematodes, aphids, and whitefly.
Yarrow is a good onion companion for similar reasons: its umbel flowers attract predatory insects like hoverflies, lacewings, and parasitic wasps that prey on pests like aphids and mites. Planting yarrow with onions in well-draining, moderately rich soil that hasn't been recently amended with manure can help to protect nearby crops from a range of pests.
What not to plant next to onions
Onions will help some companions to thrive, will tolerate others, and will actually inhibit the growth of-- or be inhibited by-- a few bad companion plants. Here's what to avoid planting with onions:
- Peas
- Beans
- Sage
- Rosemary
- Lavender
- Turnips
- Onion family plants (garlic, leeks, shallots, chives)
Companion planting peas and onions has long been thought to reduce pea yields, which is borne out by research. Beans and onions are similarly incompatible. Instead of planting onions with beans or peas, incorporating them in an annual rotation is likely to be more effective.
Rosemary and lavender both require fast draining soil without too much added compost, and they will struggle to thrive with onions' watering regimen. So, while rosemary is rumored to improve the flavor of onions, they don't make for ideal companions.
Traditionally, turnips are thought to detract from the flavor of onions. Sage is also rumored to stunt onions' growth, and doesn't share alliums' growing requirements.
Companion planting onions with other alliums like chives, leeks, garlic, garlic chives, and shallots can make them more susceptible to damage from pests and diseases. As a general rule, interplanting onion family plants with vegetables and herbs from other families will give them a better shot at growing healthily.
Pests for onion family plants
Some common onion pests include aphids, onion root maggots, nematodes, thrips, bulb mites, and leaf miners. Moving your onions to a new bed each year can help reduce the chance of damage by some of these pests. It's equally important to ensure that you harvest all of your onions at the end of the season, as any left in the ground can provide a food source for overwintering onion maggots. Good onion companions, like marigolds, will help to deter these pests or attract beneficial predatory insects.
