What Are the Best Companion Plants for Onions?
Onions grow best with lettuce, beets, peppers, strawberries and kale. 9 plants in our chart pair well with onions, mostly by deterring or trapping pests and using space and time efficiently; none of those pairings are research-supported.
| Plant | Why | Evidence |
|---|---|---|
| LettuceSpace & timing | Upright onions cast little shade and share lettuce's spacing and cool season. | Practical |
| BeetsSpace & timing | Onions and beets grow at similar spacing and pace, and upright onions don't shade beet leaves. | Practical |
| PeppersPest control | Onions fit between pepper plants, and their scent is thought to discourage aphids; the benefit is anecdotal. | Traditional |
| StrawberriesPest control | Onions along the strawberry bed edge are thought to mask the berries from pests; the benefit is anecdotal. | Traditional |
| KalePest control | Onion-family scent is said to mask kale from cabbage moths and aphids; trials show small effects at best, but the narrow, upright plants take little space. | Traditional |
| CabbagePest control | Onion-family scent is said to mask cabbage from cabbage moths and aphids; trials show small effects at best, but the narrow, upright plants take little space. | Traditional |
| BroccoliPest control | Onion-family scent is said to mask broccoli from cabbage moths and aphids; trials show small effects at best, but the narrow, upright plants take little space. | Traditional |
| CauliflowerPest control | Onion-family scent is said to mask cauliflower from cabbage moths and aphids; trials show small effects at best, but the narrow, upright plants take little space. | Traditional |
| CarrotsPest control | Onion scent may mask carrots from carrot rust flies and carrot scent may mask onions from onion flies. Trials show a benefit only when onions heavily outnumber carrots and are actively growing. | Traditional |
Good companion plants for onions, strongest evidence first.
What Should You Not Plant With Onions?
Don't plant onions near beans, peas and asparagus. The conflicts come mainly from a traditional claim of stunted growth and competition for space, light or water; none of the 3 are research-supported and the rest are practical or traditional rules.
| Plant | Why | Evidence |
|---|---|---|
| BeansClaimed growth inhibition | A widely repeated rule says onions stunt beans; it has had little controlled testing, but separating them costs nothing. | Traditional |
| PeasClaimed growth inhibition | A widely repeated rule says onions stunt peas; it has had little controlled testing, but separating them costs nothing. | Traditional |
| AsparagusCompetition | Onions are said to compete with asparagus crowns, and digging bulbs disturbs asparagus roots. | Traditional |
Plants to keep away from onions.
Which Onion Companion Claims Are Backed by Research?
None of the 12 onion pairings in our data has direct research support: 2 rest on practical horticulture and 10 are traditional claims passed down in gardening books.
Research-supported pairings rest on documented biology: shared pathogens, pollination, nematode suppression or insects that feed on specific flowers. Practical pairings are plain logic about space, shade and timing. Traditional companions such as peppers, strawberries, kale and cabbage are harmless to grow with onions, but don't rely on them for pest control — row covers, crop rotation and regular checks do more.
How Should You Plant Onions With Companions?
Plant onion sets about 4 inches (10 cm) apart in rows alternating with carrots, beets or lettuce, or along the edge of a brassica bed. Keep a bed's width between onions and beans or peas.
Companions still need room of their own, so work out how many onions and partner plants fit in a bed with the plant spacing calculator. Planting dates for onions and their companions follow your local spring and fall frost dates, so cool-season partners can be sown together in early spring or late summer for a fall crop.
Which Crops Share Companions With Onions?
Garlic, leeks and carrots share companion plants or growing conditions with onions, so their companion guides help plan the same bed or rotation.
- The guide to companion plants for garlic overlaps with this one: both crops grow well with beets, strawberries and cabbage; as members of the same plant family, the two should rotate together.
- The guide to companion plants for leeks overlaps with this one: both crops grow well with lettuce, cabbage and carrots; as members of the same plant family, the two should rotate together.
- The guide to companion plants for carrots overlaps with this one: both crops grow well with lettuce and peppers, and carrots are a good companion for onions too.
To check onions against every other plant at once, or test a whole bed plan, use the companion planting chart and garden checker.
Frequently Asked Questions
- What is the best companion plant for onions?
- Lettuce is one of the best-supported companions for onions. Upright onions cast little shade and share lettuce's spacing and cool season.
- What should you not plant with onions?
- Avoid planting onions near beans, peas and asparagus. The most important conflict is with beans: A widely repeated rule says onions stunt beans; it has had little controlled testing, but separating them costs nothing.
- Can you plant onions and garlic together?
- Yes, onions and garlic can share a bed; neither is known to help or harm the other. Both belong to the onion family (Amaryllidaceae), so they share pests and diseases — rotate them together and don't follow one with the other.
- Does companion planting really work for onions?
- Partly. None of the 12 onion pairings in our data are backed by research, 2 are practical space or timing rules, and 10 are traditional. Flowers that feed beneficial insects and separating crops that share diseases have the strongest evidence.
Companion data: PlantoScan's own editorial compilation, written from general horticultural knowledge, plant pathology and published intercropping research. Evidence labels are our editorial judgment; results vary with climate, soil, variety and pest pressure.