Companion planting
Onion Companion Plants (and What to Keep Apart)
Good onion companions are carrots, beets, lettuce, and cabbage-family crops, mostly because onions are narrow and slow and fit between bigger plants. Keep onions away from beans and peas. The pest-repelling claims are mostly folklore.
The short answer
Good onion companions: carrots, beets, lettuce, and cabbage-family crops like broccoli and cabbage. Keep onions apart from beans and peas. Be honest about why: the real benefit is space-sharing, since onions are narrow and slow and fit between bigger plants. The famous pest-repelling claims are mostly folklore.
Onion companion planting is mostly garden lore. A little of it holds up. Most of it is one gardener's hunch passed down as fact. This guide sorts the two, so you plant for reasons that actually work.
The thing to understand first is that onions are weak competitors. They are narrow, shallow-rooted, and slow. That single fact explains every pairing that genuinely matters.
Plant these with onions
The strong picks share one trait: they let a thin, upright onion fit into space a bigger plant is not using. That is real, and it is the honest reason to interplant.
| Plant with onions | Why it works |
|---|---|
| Carrots | Both are narrow and grow in the same row footprint, so you get two crops in one strip of bed |
| Beets | Another low, compact root that fills the gaps without shading the onion tops |
| Lettuce | Quick, low cover that uses ground space early, before it competes for much |
| Cabbage family (broccoli, cabbage, kale) | Onions tuck between the wider brassicas and use the open soil around them |
| Tomatoes | Onions take up little room at the base of a tall, staked tomato |
West Virginia University Extension lists the onion family alongside beets, carrots, lettuce, and the cabbage family. Notice what these pairings have in common. None of them is about onions doing something magic. They are about a slim crop sharing a bed with a bigger one.
The carrot pairing is the one most charts oversell. They claim onions drive off the carrot rust fly. Treat that as tradition, not fact. Extension sources do not back onion interplanting as a proven control for carrot rust fly, and the documented controls are crop rotation, timing, and physical row covers. Plant carrots and onions together for the space, not the pest defense.
Keep these apart from onions
The avoid list is short and softer than the charts pretend. Here is the honest version of which warnings hold up.
| Keep apart | Why (and how solid the reason is) |
|---|---|
| Beans, peas | Mostly traditional. Almost every chart says alliums stunt legumes. Extension sources call the evidence anecdotal, not proven. Plant them apart if you want, but it is not a hard law. |
| Any thirsty, leafy neighbor | Well supported. Onions are poor competitors. A plant that shades them or drinks the water first will shrink the bulbs. Crowding is the real enemy. |
The bean-and-pea rule is the famous one, and it deserves an honest label. University of Illinois Extension is direct that much companion advice is not tested in research and is passed down from gardeners who grew two plants together and felt they did or did not get along. The onion-bean caution sits squarely in that bucket.
So keep beans and peas a row or two over if it makes you feel better. Just know you are following tradition, not a trial.
What actually works, and what is just lore
Here is the clean split between the mechanisms with evidence and the claims without.
Space-sharing works. Tucking a narrow onion between carrots, beets, or brassicas grows more food in the same bed. This is plain bed design, and it is the best-supported reason to interplant onions.
The pest-repelling reputation is weak. The idea that onion scent drives off aphids, rabbits, and deer is mostly folklore. Some older trials hint at a small effect on aphids near other crops, but University of Minnesota Extension is clear that many popular companion claims are not backed by research. Do not plant onions as a guard.
The flavor claims are tradition. Charts that say chamomile or summer savory sweetens your onions are passing down lore, not findings. There is no trial behind it. The plants are harmless neighbors either way.
Note
Much onion companion lore is untested. Do not bet your harvest on a chart. The safe, proven wins are simple: give onions full sun and room, never let a leafy neighbor shade or out-drink them, and use their narrow shape to share space with bigger crops. Everything past that is a low-risk experiment, not a guarantee.
A sample bed layout
Picture a 4x8 raised bed (about 1.2 x 2.4 m). Run the rows the long way, 8 feet across.
Give the middle of the bed to a wide crop like cabbage or broccoli, spaced for full size. Then line both edges with onions and carrots in alternating short rows. The onions sit 5 inches apart, the carrots 3 inches apart, and neither shades the other.
NC State Extension puts onions 3 to 4 inches apart for full bulbs, and 5 inches is a safe garden default that keeps air moving. The point of the layout is not a pest shield. It is three crops pulling from one bed without fighting for light or water.
Pro tip
Plant onions on the sunny, open edge of the bed, not buried in the middle behind tall plants. They are short and they hate shade. An onion that spends the afternoon under a tomato canopy makes a small bulb, no matter how good the "companion" chart says the pairing is.
Spacing and sun beat every companion trick
A well-placed onion in full sun outgrows any companion plant a chart can promise you. Onions need light and water that nothing else is stealing.
So before you plan an elaborate companion bed, get the basics right. Most onions want about 5 inches between plants in rows roughly 12 inches apart, and a spot that gets sun all day. Our guide on how far apart to plant onions has the full spacing, and when to plant onions covers the timing.
Common mistake
The two errors that undo good intentions. Crowding onions in the name of companionship packs them so tight, or so deep in the shade of a leafy neighbor, that the bulbs stay small. A companion that costs an onion its sun or water is a net loss. The second is trusting the pest-repelling charts and skipping real pest control because you planted onions nearby. The scent does not guard the bed.
Your next step
Plant carrots, beets, lettuce, or brassicas with your onions to share the bed, and keep beans and peas a row over if you follow the tradition. The honest win is space and sun, not pest magic. Treat the rest of the companion chart as a low-risk experiment.
The biggest lever is giving each onion full light and room. Read how far apart to plant onions to set the spacing, then sort the same evidence-versus-folklore question for the rest of the bed in tomato companion plants and cucumber companion plants.
Common questions
What should not be planted near onions?
Traditional companion charts say to keep onions away from beans and peas, and most extension guides repeat that advice. The honest caveat is that the reason is largely anecdotal, not proven in field trials. The firmer rule is to not crowd onions. They are poor competitors, so any thirsty, leafy neighbor that shades them or steals water will cost you bulb size.
What grows well with onions?
Carrots, beets, lettuce, and cabbage-family crops are the usual picks, and they pair well for a practical reason. Onions are narrow, upright, and slow, so they tuck into the gaps between bigger plants without crowding them. West Virginia University Extension lists the onion family alongside beets, carrots, lettuce, and the cabbage family. The space-sharing is real. The pest-repelling is mostly folklore.
Can you plant onions and carrots together?
Yes, and it is a sensible pairing. Both are narrow crops that fit in the same row without crowding, so you grow two in one footprint. The popular claim that onions drive off the carrot rust fly is the folklore part. University extension guidance treats it as traditional advice, not a proven control. Plant them together for the space saving, not the pest magic.
Do onions repel pests in the garden?
Mostly no, despite what the charts say. The idea that onion scent drives off aphids, rabbits, and deer is traditional companion-planting lore with little research behind it. Some older trials hint at a small effect on aphids, but extension sources are clear that most of these claims are not backed by data. Do not plant onions expecting them to guard the bed.
Is onion companion planting backed by science?
Parts of it. Sharing space between a narrow crop and a bigger one is just good bed design, and that holds up. The specific pairings, the flavor claims, and the pest-repelling reputation are mostly anecdotal. University of Illinois Extension is blunt that much companion advice is passed down from gardeners rather than tested in trials. Treat the chart as a starting point.
Sources
Agronomic claims in this guide are checked against these primary sources.
- Companion planting in home gardens — University of Minnesota Extension
- Companion Planting: Anecdotal or Tried and Tested? — University of Illinois Extension
- Onions, Leeks, Green Onions, Shallots, and Garlic — NC State Extension
- Companion Planting — West Virginia University Extension
Keep reading
Tomato Companion Plants (and What to Keep Apart)
Good tomato companions include basil, marigold, nasturtium, garlic, onion, lettuce, and carrots. Keep tomatoes away from brassicas, fennel, potatoes, and black walnut. The proven wins are pollinator support and spacing, not magic flavor changes.
Read →Cucumber Companion Plants (and What to Keep Apart)
Good cucumber companions are beans and peas for nitrogen and vertical layering, corn or sunflowers for support, and flowers like nasturtium and dill to draw pollinators. The honest win is anything that brings bees, since most cucumbers need them to set fruit.
Read →When to Plant Onions (Spring Timing by Zone)
Plant onions as early as the soil can be worked in spring, about 2 to 4 weeks before your last frost, once soil hits 50 F. In the Deep South, short-day onions go in during fall instead. Match the onion type to your latitude.
Read →Zucchini Companion Plants (and What to Keep Apart)
Good zucchini companions are flowers like nasturtium and borage that pull in the bees zucchini needs to set fruit, plus beans and corn. Keep zucchini away from other squash and cucumbers, which share its pests. Most "avoid" charts are folklore.
Read →Spinach Companion Plants (and What to Keep Apart)
Good spinach companions are tall shade-givers like beans and corn, quick neighbors like radishes and lettuce, and flowers for pollinators. Keep spinach from chard and beets, which share leaf miners. Most pairing rules are folklore, so plant for shade, spacing, and pest sense.
Read →Pepper Companion Plants (and What to Keep Apart)
Good neighbors for peppers include basil, onions and garlic, carrots, lettuce and spinach, nasturtium, and tomatoes. Keep fennel and heavy-feeding brassicas apart. The reliable wins are spacing, pollinator support, and not crowding, not flavor magic.
Read →