Onion Companion Plants
Vegetable100 days to maturity
The onion is a biennial bulb grown as an annual, and its bulbing is triggered by day length, so varieties are sold as short-day, intermediate-day, or long-day types matched to your latitude. Its pungent sulfur compounds make it one of the best natural pest deterrents in the garden, confusing and repelling many insects. Onions are mostly troubled by onion maggots tunneling the bulbs, thrips streaking the leaves, and bolting when temperatures swing.
Companion Checker: what grows well with Onion?
Tap any plant to see whether it pairs well with Onion and why. Green means a beneficial companion, red means keep them apart.
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Companion Planting Strategy for Onion
Onions take up almost no above-ground room and emit a strong scent that masks the smell of nearby crops, so the companion strategy is to weave them among vegetables plagued by their own pests. The same alliums that protect carrots and brassicas, however, chemically interfere with legumes, so beans and peas must be kept well apart.
Best Companion Plants for Onion
These plants grow well alongside Onion — providing pest control, attracting pollinators, or making better use of your garden space.
The onion's strong scent helps repel and confuse the carrot rust fly, while the carrots in turn help deter onion flies, a classic case of mutual protection.
Onions take up little above-ground space and their pungent odor deters aphids and browsing rabbits from nearby lettuce, with no real root competition.
Onions and beets root at different depths so they do not compete, and the onion's scent helps mask the bed from pests, making them efficient neighbors.
What Not to Plant With Onion
Keep these away from Onion. They compete for resources, attract shared pests, or inhibit each other's growth.
How to Grow Onion
- Botanical name
- Allium cepa
- Family
- Amaryllis (Amaryllidaceae)
- Sun
- Full sun, 6+ hours daily
- Water
- About 1 inch per week, kept consistent; taper off as tops begin to fall over near harvest
- Soil
- Loose, fertile, well-draining soil, pH 6.0-7.0
- Spacing
- 4-6 inches apart in rows 12-18 inches apart
- Planting depth
- Plant sets about 1 inch deep; sow seed 1/4-1/2 inch deep
- Germination
- 7-14 days at 65-75F
- Days to maturity
- 90-120 days from seed, or about 60-80 days from sets
- When to plant
- Set out sets or transplants in early spring as soon as soil is workable, or in fall for overwintering, choosing a day-length type suited to your latitude
- Harvest
- Lift when the tops yellow and flop over, then cure in a dry, airy, shaded spot for 2-3 weeks before storing
Common Onion Problems
Onion maggot (white larvae tunneling into bulbs, causing wilting)
Use floating row covers, rotate crops away from where alliums grew, avoid fresh manure, and promptly remove and destroy any infested or culled bulbs.
Thrips (silvery streaks and stippling on the leaves)
Knock them back with strong water sprays, apply insecticidal soap or neem oil, hang blue sticky traps, and encourage predatory insects like lacewings.
Downy mildew and neck rot (gray or purple fuzzy growth, soft rotting necks)
Rotate crops, space for airflow, avoid overhead watering, and cure bulbs thoroughly before storing in a cool, dry place to prevent storage rot.
Bolting (premature flower stalk forming)
Triggered by temperature swings or oversized sets; plant small sets, set them out at the right time, and snap off any flower stalks as soon as they appear to redirect energy to the bulb.
Onion Companion Planting FAQ
What are the best companion plants for onions?
Carrots, beets, and lettuce are top companions for onions, along with other brassicas like cabbage and broccoli. The onion's strong scent confuses pests such as the carrot rust fly, while it competes little for space, and crops like carrots return the favor by deterring onion flies.
What should you not plant with onions?
Keep onions away from beans and peas, since onions and other alliums release compounds that stunt legume growth and interfere with the nitrogen-fixing bacteria on their roots. Other legumes are best kept in separate beds for the same reason.
How far apart should you plant onions?
Space onions 4-6 inches apart in rows 12-18 inches apart so each bulb has room to size up fully. Tighter spacing around 2-3 inches works if you plan to harvest some early as green onions, thinning as you go.
Why are my onions not forming bulbs?
The most common reason is planting the wrong day-length type for your latitude, since bulbing is triggered by day length: long-day onions suit northern gardens and short-day types suit the South. Crowding, too much shade, and excess nitrogen can also leave you with lush tops but small or no bulbs.
More vegetable companions
Plan Your Onion Garden
Use our interactive tools to design the perfect garden with Onion and its companions.