23 Best Onion Companion Plants (with Chart) & 7 to Avoid

Q: What soil is best for onion companions?

Onions and their companions perform best in loamy, well-draining soil that’s rich in organic matter. I aim for a pH around 6.0 to 7.0. Avoid soggy or compacted soil—onions hate wet feet. If your soil tends to hold water, mix in some coarse sand or leaf mold to improve drainage. Good soil is the foundation of companion planting success.

Q: Do onions need full sun to benefit from companion planting?

Absolutely. Onions are sun lovers and need at least 6–8 hours of direct sunlight daily . The same goes for most of their best companions—like carrots, dill, and basil. Without strong light, you’ll get smaller bulbs and slower growth. If your garden is partially shaded, prioritize sun for your onion beds and keep companions that tolerate less light nearby.

Growing onions sounds easy—until pests show up, the bulbs stay small, or your garden feels overcrowded. That’s when companion planting can make a real difference.

Companion planting means growing plants together that help each other thrive. For onions, it’s about choosing neighbors that boost flavor, save space, and fight off pests—like carrots, which benefit from onions’ smell while protecting them in return.

In this guide, I’ll show you the best plants to grow with onions—organized by vegetables, herbs, and flowers—along with the plants you should never pair with them. I’ve also created a free companion planting chart you can download and use in your garden.

Let’s give your onions the right garden partners.

🌿 Benefits of Companion Planting for Onions

Pairing onions with the right plants can help your entire garden grow better.

Natural pest repellent: The strong onion smell keeps away aphids, carrot flies, and more.
Smart root spacing: Onions have shallow roots, so they pair well with deep-rooted or leafy plants.
Flavor boost: Some herbs like chamomile and summer savory can actually improve onion taste.
More in less space: Companion planting helps you grow more—even in small beds or containers.

23 Companion Plants for Onions:

🥕 Vegetables:

1. Carrots (Daucus carota subsp. sativus)

Carrots and onions make one of the best companion pairs. Their different root depths prevent competition, and their scents confuse each other’s pests—carrot fly and onion fly. This natural deterrent system can help you grow both crops with fewer pest problems and better yields, especially in compact garden spaces.

Best for: Pest control, small raised beds
Hardiness Zone: 3–10
Mature Size: 6–12 in. tall, 1–2 in. wide roots
When to Plant: Early spring or fall
Care Requirements: Full sun, loose well-draining soil, regular watering

Related: Best Carrot Companion Plants

2. Lettuce (Lactuca sativa)

Lettuce acts as a living mulch when planted with onions. It keeps the soil moist, suppresses weeds, and makes great use of space while onions grow slowly. Their shallow roots mean no competition, making lettuce a great crop to tuck around onions during cool-weather seasons.

Best for: Moisture retention, weed suppression
Hardiness Zone: 4–9
Mature Size: 6–12 in. tall and wide
When to Plant: Early spring or late summer
Care Requirements: Partial to full sun, consistent moisture, fertile soil

3. Beets (Beta vulgaris)

Beets and onions share similar growing needs, making them natural garden companions. Beets help shade the soil, reduce water evaporation, and improve structure over time. Since they don’t compete for nutrients, you can plant them close together in raised beds or rows for efficient use of space.

Best for: Space-saving, shared soil needs
Hardiness Zone: 2–10
Mature Size: 12–18 in. tall, 2–4 in. root width
When to Plant: Early spring or fall
Care Requirements: Full sun, moist and fertile soil, regular thinning

4. Radishes (Raphanus sativus)

Fast-growing radishes are a smart interplanting option for onions. Their roots loosen the soil, allowing onion bulbs to expand easily. They also mature quickly, giving you a harvest within weeks and clearing space for onions to develop later in the season.

Best for: Soil loosening, quick harvest
Hardiness Zone: 2–11
Mature Size: 6–12 in. tall, 1–2 in. roots
When to Plant: Early spring or late summer
Care Requirements: Full sun, well-draining soil, frequent watering

5. Spinach (Spinacia oleracea)

Spinach grows well with onions thanks to its compact growth and quick maturity. It benefits from the onion’s pest-repelling scent while providing ground cover that reduces weeds and moisture loss. These two crops don’t compete, so they thrive in shared beds or containers.

Best for: Quick harvest, companion containers
Hardiness Zone: 3–9
Mature Size: 6–12 in. tall, 6–10 in. wide
When to Plant: Early spring or fall
Care Requirements: Partial shade to full sun, cool temperatures, moist soil

6. Celery (Apium graveolens)

Celery’s mild aroma helps confuse onion pests while its upright habit avoids crowding onion bulbs. Their differing root zones make them a great pairing in garden beds, and both enjoy similar watering needs. Together, they create a productive and pest-resilient planting area.

Best for: Raised beds, pest confusion
Hardiness Zone: 4–10
Mature Size: 18–24 in. tall, 12–18 in. wide
When to Plant: After frost in spring
Care Requirements: Full sun, fertile soil, consistent moisture

7. Swiss Chard (Beta vulgaris var. cicla)

Swiss chard thrives near onions due to its tolerance for similar soil and sun conditions. Its large, leafy canopy shades the ground, helping preserve moisture for onions. Since chard roots go deeper, it won’t interfere with onion bulb development, making it a solid companion choice.

Best for: Moisture control, visual contrast
Hardiness Zone: 3–10
Mature Size: 12–24 in. tall, 12–18 in. wide
When to Plant: Spring to early summer
Care Requirements: Full sun to partial shade, rich soil, even watering

8. Tomatoes (Solanum lycopersicum)

Tomatoes and onions grow well together in warm-season beds. Onions act as a natural insect repellent, keeping aphids and beetles away from your tomato plants. With different growth heights and root systems, they coexist without crowding or nutrient struggles.

Best for: Pest control in warm beds
Hardiness Zone: 4–11
Mature Size: 3–6 ft. tall, 2–3 ft. wide
When to Plant: After last frost
Care Requirements: Full sun, regular watering, well-draining soil

9. Peppers (Capsicum annuum)

Onions help deter aphids, slugs, and beetles that commonly target peppers. Since onions stay compact and upright, they don’t compete with peppers for space. This pairing is great for containers or garden rows where airflow and pest prevention are priorities.

Best for: Compact companion planting
Hardiness Zone: 4–11
Mature Size: 18–36 in. tall, 12–18 in. wide
When to Plant: Late spring
Care Requirements: Full sun, warm soil, regular feeding

Must Read: Pepper Companion Plants (with Chart)

10. Potatoes (Solanum tuberosum)

Potatoes benefit from onion companions by facing fewer pest issues, especially from moths and beetles. Since both are root crops, spacing is important—but when done right, this pair helps each other thrive in a shared plot without extra intervention.

Best for: Natural pest deterrent
Hardiness Zone: 3–10
Mature Size: 1–3 ft. tall, underground tubers
When to Plant: Early spring
Care Requirements: Loose soil, full sun, consistent watering

11. Parsnips (Pastinaca sativa)

Parsnips grow deeper than onions and don’t compete for root space. They also benefit from onion’s ability to repel voles and burrowing pests. These two cool-season crops make a solid pair for spring or fall planting.

Best for: Cool-season row gardens
Hardiness Zone: 2–9
Mature Size: 12–24 in. tall, 2–3 in. wide roots
When to Plant: Early spring or late summer
Care Requirements: Full sun, deep, loose soil, steady moisture

🌿 Herbs:

12. Dill (Anethum graveolens)

Dill is a flavor booster and pest fighter when planted near onions. It can subtly enhance the taste of your onion bulbs while drawing in natural predators like hoverflies and parasitic wasps that feed on aphids. This makes dill a smart pick for gardeners who want healthier onions without chemical sprays.

Best for: Onion flavor and pest protection
Hardiness Zone: 2–11
Mature Size: 2–5 ft. tall, 1–2 ft. wide
When to Plant: Early spring after frost
Care Requirements: Full sun, well-drained soil, moderate moisture

13. Chamomile (Matricaria chamomilla)

Chamomile brings more than calming tea benefits—it helps onions too. This delicate herb enhances onion flavor and attracts beneficial insects like hoverflies that keep aphid populations in check. It also has antifungal qualities that may improve the overall health of nearby plants in your garden bed.

Best for: Flavor, aphid control, and plant health
Hardiness Zone: 3–9
Mature Size: 12–30 in. tall, 8–12 in. wide
When to Plant: Spring or fall
Care Requirements: Full sun, light soil, moderate watering

14. Summer Savory (Satureja hortensis)

This underused herb is a top-tier onion companion. Summer savory not only improves the sweetness and flavor of onion bulbs, but also encourages faster growth. It’s ideal for gardeners who want to give their onions a gentle push toward better size and taste, all while adding a culinary herb to the mix.

Best for: Boosting onion sweetness and growth
Hardiness Zone: 2–11
Mature Size: 12–24 in. tall, 12–18 in. wide
When to Plant: After last frost
Care Requirements: Full sun, slightly alkaline soil, light watering

15. Thyme (Thymus vulgaris)

Thyme acts as a living mulch around onions. Its low, spreading growth helps suppress weeds and conserve moisture while repelling pests like onion flies. With no risk of overcrowding, thyme is perfect for tucking in around onion rows in raised beds or containers.

Best for: Weed control and pest repelling
Hardiness Zone: 5–9
Mature Size: 6–12 in. tall, 12–18 in. wide
When to Plant: Spring after frost or fall
Care Requirements: Full sun, well-drained soil, drought-tolerant

16. Basil (Ocimum basilicum)

Basil helps protect onions from aphids and flies while adding aromatic diversity to your garden. Though more commonly paired with tomatoes, basil fits well near onions and supports biodiversity by attracting pollinators and repelling harmful insects.

Best for: Insect repelling and pollinator support
Hardiness Zone: 4–10
Mature Size: 12–24 in. tall, 12–18 in. wide
When to Plant: After last frost
Care Requirements: Full sun, rich soil, regular watering

17. Rosemary (Salvia rosmarinus)

Rosemary offers double-duty benefits in an onion bed. Its aromatic oils repel insects like carrot flies and onion flies, while its tall, woody stems provide some light shade to shallow-rooted onion crops. Just be sure your soil drains well—rosemary won’t tolerate soggy roots.

Best for: Pest control and partial shading
Hardiness Zone: 8–10
Mature Size: 3–5 ft. tall, 2–4 ft. wide
When to Plant: Spring, after danger of frost
Care Requirements: Full sun, dry soil, minimal watering once established

Must Read: Rosemary Companion Plants (with Chart)

18. Rue (Ruta graveolens)

Rue’s strong fragrance masks the scent of onions, helping deter onion root flies. It acts almost like a scent shield, confusing pests that are drawn to onion plants. Use rue sparingly and never near edible herbs—its potency can interfere with more delicate companions.

Best for: Pest masking, especially root fly deterrence
Hardiness Zone: 4–10
Mature Size: 24–36 in. tall and wide
When to Plant: Spring after frost
Care Requirements: Full sun, well-drained soil, drought-tolerant

19. Parsley (Petroselinum crispum)

Parsley plays a similar role to carrots in the onion bed. It attracts beneficial insects like predatory wasps and hoverflies while subtly protecting onions from soft-bodied pests. It’s also a compact plant that won’t compete with onions for space.

Best for: Companion pest control, garden diversity
Hardiness Zone: 4–9
Mature Size: 10–18 in. tall, 9–12 in. wide
When to Plant: Early spring or late summer
Care Requirements: Partial to full sun, moist fertile soil

20. Mint (Mentha spp.)

Mint is powerful at repelling onion flies, but it comes with a warning—its roots spread fast. To enjoy the benefits without the chaos, grow mint in pots and place them near your onions. This keeps the pests away without letting mint take over your bed.

Best for: Onion fly control (container-only)
Hardiness Zone: 3–10
Mature Size: 12–24 in. tall, vigorous spreader
When to Plant: Spring after frost
Care Requirements: Partial shade to full sun, rich moist soil, keep contained

🌸 Flowers

21. Marigolds (Tagetes spp.)

Marigolds are a must-have in any onion companion planting setup. Their strong scent repels nematodes, aphids, and onion flies—three pests onions don’t need in their soil or on their leaves. Bonus: marigolds attract pollinators too, creating a healthier, more balanced garden.

Best for: Insect control and pollinator support
Hardiness Zone: 2–11
Mature Size: 6–36 in. tall, 6–24 in. wide
When to Plant: After last frost in spring
Care Requirements: Full sun, well-drained soil, low to moderate watering

22. Roses (Rosa spp.)

You might not think of onions and roses as compatible, but they’re great partners. Aphids love roses, but not the strong aroma of nearby onions. Planting onions around your rose beds can reduce aphid pressure and keep your blooms looking their best—without relying on chemical sprays.

Best for: Aphid deterrence in ornamental gardens
Hardiness Zone: 3–10 (varies by variety)
Mature Size: 1–6 ft. tall, 1–4 ft. wide
When to Plant: Spring or fall
Care Requirements: Full sun, rich well-draining soil, regular watering

23. Chrysanthemums (Chrysanthemum spp.)

Chrysanthemums are beautiful bloomers that also deter aphids, especially when planted with chives or other onion relatives. If you want a flowering border that protects your crops while brightening the garden, chrysanthemums paired with onions or chives make a great low-maintenance solution.

Best for: Natural pest management in mixed beds
Hardiness Zone: 5–9
Mature Size: 1–3 ft. tall and wide
When to Plant: Spring or fall
Care Requirements: Full sun, fertile well-drained soil, moderate water needs

Must Read: Flowers That Bloom at Night – Our Favorite Picks

Onion Companion Planting Chart (Downloadable)

Here’s a quick-reference chart for onion companion planting that you can print or save to help plan your onion-friendly garden. Use it for raised beds, containers, or row gardens—it’s an easy way to ensure every plant you grow supports healthy onions.

📥 Steps to Download This Onion Companion Planting Chart

On Desktop/PC:

Chrome: Right-click the image and select “Save image as…”
Safari (Mac): Control-click the image and choose “Save Image to Downloads” or “Save Image As…”

On Mobile Devices:

Android: Tap and hold the image → Select “Download image”
iOS (iPhone/iPad): Tap and hold the image → Choose “Add to Photos”

What Not to Plant with Onions (and Why)

While onions are generally great companions, some plants just don’t get along with them. Here are 7 plants you should avoid planting near your onions—and the reasons why:

Beans (Phaseolus spp.): Beans, especially pole varieties, interfere with onion growth by competing for nutrients and altering soil nitrogen levels. Onions prefer stable conditions and may become stunted when grown nearby.
Peas (Pisum sativum): Like beans, peas fix nitrogen in the soil and can disrupt the balance onions need. Their vining nature can also overwhelm onions by stealing space and light.
Asparagus (Asparagus officinalis): Both onions and asparagus are heavy feeders and deep-rooted. Planting them together creates a turf war underground, leading to reduced growth on both sides.
Turnips (Brassica rapa): Turnips need a lot of space to develop properly, and they’ll compete with onions for both nutrients and root room. This leads to underdeveloped bulbs in both crops.
Garlic (Allium sativum): Garlic and onions share similar diseases and pests, especially onion maggots. Growing them side by side increases the risk of cross-infestation.
Shallots/Chives (Allium cepa var. aggregatum / Allium schoenoprasum): These onion relatives attract the same pests and diseases, making them risky to grow near your onions. Keep all alliums spaced out in your garden.
Sage (Salvia officinalis): Sage releases allelopathic compounds that can hinder onion growth. While great near carrots or beans, sage is best kept far from your onion beds.

FAQs About Onion Companion Planting

Can I plant onions and tomatoes together?

Yes, and I recommend it. I’ve grown tomatoes alongside onions for years without a hitch. Onions repel pests like aphids and beetles that often attack tomato plants, and since their roots occupy different zones, there’s no competition underground. Just be mindful of spacing to allow air circulation, and you’ll have a thriving, pest-resistant combo.

Do onions grow well in containers with other plants?

They do—and quite successfully. I often grow bunching onions in wide containers alongside shallow-rooted herbs like thyme or greens like lettuce. The key is choosing a container that’s at least 8–10 inches deep with excellent drainage. Add compost-rich soil, water regularly, and you’ll be surprised how much you can grow in a small space.

What soil is best for onion companions?

Onions and their companions perform best in loamy, well-draining soil that’s rich in organic matter. I aim for a pH around 6.0 to 7.0. Avoid soggy or compacted soil—onions hate wet feet. If your soil tends to hold water, mix in some coarse sand or leaf mold to improve drainage. Good soil is the foundation of companion planting success.

Do onions need full sun to benefit from companion planting?

Absolutely. Onions are sun lovers and need at least 6–8 hours of direct sunlight daily. The same goes for most of their best companions—like carrots, dill, and basil. Without strong light, you’ll get smaller bulbs and slower growth. If your garden is partially shaded, prioritize sun for your onion beds and keep companions that tolerate less light nearby.

Can I use companion planting with onions in raised beds?

Yes, and I do this regularly. Raised beds are one of the best places to try companion planting with onions. They give you control over spacing, soil mix, and watering. I like to plant onions in the center, with fast-growing crops like radishes or leafy greens around them. Add marigolds or thyme near the edges to help with pest control.

Must Read: Broccoli Companion Plants (with Chart)

Conclusion

In my years of gardening, onions have never let me down—as long as they have the right neighbors. Whether it’s carrots deterring flies, lettuce helping the soil stay cool, or marigolds keeping pests away, I’ve seen firsthand how companion planting brings out the best in onions.

It’s not just about pairing plants—it’s about creating a balanced, cooperative environment where every square foot works smarter.

I hope this guide gives you the tools and inspiration to try onion companion planting in your own space—whether it’s a sprawling raised bed or a few containers on a sunny patio.

💡 Don’t forget to download the printable companion planting chart and keep it nearby—it’s a quick reminder of what to grow together and what to keep apart.

Now it’s your turn!

Have you tried growing onions with other crops or flowers? What’s worked (or hasn’t) in your garden?

Share your stories or questions in the comments—I’d love to hear them. And if you’d like more expert guides like this, join our Gardening newsletter and let’s keep growing together.

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