What Grows Well With Onions? 10 Best Companion Plants and How to Grow Them

Introduction: Why asking what grows well with onions matters

Companion planting can turn an average onion bed into a productive, pest-resistant mini-ecosystem. Pairing onions with the right plants reduces pests, boosts flavor, saves space, and fills soil nutrients, so you harvest more without extra work. Think carrot rows shielded from carrot fly by onions, or brassicas that benefit from onion scent keeping cabbage moths away.

So what grows well with onions? This article gives 10 proven companion plants, plus exact planting distances, timing, and simple care tips you can use on your next planting day. You will get specific combos that work in raised beds, containers, and traditional rows, plus quick fixes for common problems like bulb rot and onion maggots.

Expect very actionable advice, for example plant lettuce between onion rows to maximize space and keep soil shaded, sow carrot seeds at the same time as sets for staggered harvests, and put herbs like chamomile and dill nearby to attract beneficial insects. Read on for step-by-step pairings and the few plants you should avoid near onions.

Quick answer: Best companions at a glance

If you want a fast answer to what grows well with onions? try these: carrots (great pairing, they confuse each other’s pests), beets (different root depth, minimal competition), lettuce and spinach (quick, cool-season crops that use space above onions), cabbage family plants like cabbage and broccoli (onions help repel cabbage moths), tomatoes and peppers (benefit from onion pest-repelling scent), strawberries and herbs such as chamomile and parsley (improve flavor and attract beneficial insects), plus marigolds for nematode and general pest control. Plant in alternating rows or interplant thinly, and avoid beans and peas which can struggle near onions.

Why companion planting helps onions

Companion planting does three things for onions that actually move the needle: it cuts pests, saves space, and boosts overall yield. For pest reduction, plant onions next to cabbage or broccoli to deter cabbage moths, and tuck marigolds nearby to reduce soil nematodes. For space efficiency, sow quick crops like lettuce or radishes between onion rows, harvest those early, then let onions fill the space. For yield improvement, pair onions with deep rooted crops such as tomatoes or beets so roots do not compete, and add flowering herbs like dill or chamomile to attract parasitic wasps that eat aphids. If you are asking what grows well with onions? Start with carrots, lettuce, beets, brassicas, and marigolds, and avoid planting onions next to beans or peas.

Top 7 companion plants for onions and how to plant them

If you ask what grows well with onions, these seven are the easiest and most reliable pairs, with exact planting tips so you can get it right.

1. Carrots. Why: onions repel carrot fly, carrots help break up soil. Planting tips: sow carrot seed 1/4 inch (0.5 cm) deep, thin to 2 to 3 inches (5 to 8 cm) between plants. Space onion sets 4 to 6 inches (10 to 15 cm) apart in the same row, or interplant carrots between onion sets; sow carrots as soon as soil can be worked.

2. Beets. Why: similar watering needs, minimal root competition. Planting tips: sow beet seed 1/2 inch (1.25 cm) deep, thin to 3 to 4 inches (7 to 10 cm). Onions can be in the same bed, spaced 4 to 6 inches apart; plant beets in spring with onions for staggered harvest.

3. Lettuce. Why: lettuce matures fast, uses the shade between onion rows, and benefits from pest protection. Planting tips: sow lettuce very shallow, thin to 6 to 8 inches (15 to 20 cm) for heads, 4 inches for leaf lettuce. Start lettuce early spring or late summer, and harvest before onion bulbs need more space.

4. Tomatoes. Why: onions deter aphids and some fungal pests, tomatoes tolerate close onion neighbors. Planting tips: transplant tomatoes after last frost, set them 12 to 18 inches (30 to 45 cm) from onion rows so roots do not compete. Mulch to retain moisture.

5. Strawberries. Why: onions reduce pests that attack strawberries, and plants do not compete heavily. Planting tips: set strawberry crowns 12 to 18 inches (30 to 45 cm) apart, plant onions in between or along the border; plant both in spring or stagger strawberries in fall.

6. Chamomile. Why: attracts beneficial insects and improves nearby plant health. Planting tips: sow chamomile seed on the surface in spring, thin to 8 to 12 inches (20 to 30 cm). Use as a low border around onions.

7. Parsley. Why: deep taproot, attracts predatory insects, compatible water needs. Planting tips: sow parsley 1/4 inch (0.5 cm) deep, thin to 6 to 8 inches (15 to 20 cm). Start parsley at the same time as onion seedlings for continuous companion benefits.

Plants to avoid near onions and why

Not every plant pairs well with onions. First, avoid legumes such as bush beans, pole beans, and peas. Onions emit sulfur compounds that can reduce nitrogen-fixing activity, so beans often yield poorly when crowded by onions. Second, keep fennel well away, it is strongly allelopathic and suppresses growth of many vegetables. Third, be cautious with potatoes and other solanums, they can share pests and compete for similar nutrients in dense beds. Safe alternatives if you ask what grows well with onions? Plant carrots, beets, lettuce, chard, and brassicas nearby, or move beans and fennel to a separate bed or container.

How to plant onions with companions step by step

1. Prep the bed, make raised rows if drainage is poor, and dedicate 12 to 18 inches of walkable space between onion rows for access. Place taller companions like tomatoes or peppers to the south so they do not shade onions.

2. Timing, plant onion sets or transplants as soon as soil is workable, usually 2 to 4 weeks before last frost. Sow cool companions like carrots and spinach at the same time. Transplant warm-season crops after the last frost.

3. Spacing, set bulb onions 4 to 6 inches apart, bunching onions 2 to 3 inches. Sow carrot seeds 2 to 3 inches apart, beets 3 to 4 inches, lettuce 8 to 12 inches. Scatter marigolds every 8 to 10 inches for pest control.

4. Succession planting, harvest spring onions early, then sow fast crops such as basil or bush beans. Stagger lettuce every 2 weeks to keep steady harvests. That answers what grows well with onions, with a practical planting plan.

Soil, water, and feeding tips for mixed beds

Start with a soil test, then bring the bed to life with 2 inches of compost worked into the top 6 inches of soil, pH 6.0 to 7.0. That baseline feeds onions and most companion plants, from carrots to lettuce. Water deeply, not often; aim for about 1 inch of water per week, more in hot weather. Use drip irrigation or soaker hoses to keep foliage dry and reduce disease.

Fertilize at planting with a balanced granular fertilizer, following label rates for the area. Side-dress onions and leafy companions once when tops reach 6 inches, using a nitrogen boost like blood meal or a low analysis fertilizer. Stop heavy feeding when bulbs begin to swell, and mulch 2 to 3 inches to retain moisture and suppress weeds.

Using companion plants for pest and disease control

Use trap crops to pull pests away from onions, for example plant nasturtiums at the bed edge to attract aphids and whiteflies, then remove or hose off heavily infested plants. Sow buckwheat or sweet alyssum in strips to bloom fast, they lure parasitic wasps and hoverflies that eat onion aphids and caterpillars. Border beds with French marigolds to help reduce soil nematodes and some root pests, planting one per square foot near onions.

Simple monitoring stops problems early, use yellow sticky traps at canopy height to catch thrips and onion flies, check weekly and replace every two weeks. Lift random bulbs midseason to inspect for maggots, and use floating row covers during peak egg laying to protect young sets. What grows well with onions matters for pest control.

Two sample layouts: a small raised bed and a container plan

Small raised bed, 4 by 4 feet, soil well-drained: two 4-foot onion rows, 8 sets per row, spacing 6 inches, total 16 onions. Between the onion rows plant two staggered carrot rows, 24 carrots each at 2 inch spacing. Edge the bed with 8 lettuce heads spaced 10 inches apart, sowing lettuce every 2 weeks for continuous harvest. Planting timing, set onion sets early spring or fall, sow carrots at same time, transplant lettuce after seedlings reach 3 inches.

Container plan, 18 inch diameter, 12 inch deep: plant 6 onions at 6 inch spacing around the perimeter, fill center with 6 quick maturing radishes spaced 3 inches. Radishes are done in 4 weeks, replace with basil or chives. This answers what grows well with onions, and gives an easy, copyable layout.

Conclusion and quick checklist

Companion planting with onions is low effort, high reward. Use this quick checklist to get results fast.

Do:

1. Plant carrots, beets, lettuce, and strawberries nearby, they thrive next to onions and save space.
2. Space bulbs 4 to 6 inches apart for salad onions, 6 to 8 inches for larger varieties, and water consistently.
3. Rotate beds yearly to prevent onion pests and disease buildup.
4. Use aromatic allies like chamomile or nasturtiums to attract beneficial insects and repel pests.

Don’t:

1. Plant beans or peas next to onions; legumes often struggle near alliums.
2. Crowd onions; poor air flow causes rot.

Final tip: if you’re wondering what grows well with onions, try small test beds, keep notes, and scale what works for you. Companion planting rewards experimentation.