Onions are a staple crop in home gardens around the world. Beyond their culinary uses, onions offer incredible benefits when used strategically in companion planting. Their pungent aroma and chemical compounds make them excellent neighbors for repelling pests and enhancing the growth of specific crops. However, not all plants pair well with onions. Selecting the right companion plants can boost productivity, reduce disease, and deter harmful insects. In this guide, we’ll explore 16 of the best companion plants to grow alongside onions, detailing how each plant contributes to a healthier, more balanced garden.

1. Carrots

Carrots and onions are classic companions. Onions repel carrot flies with their strong smell, which helps protect the delicate carrot foliage. In return, carrots do not interfere with onion growth and can be planted in alternating rows to maximize space. This partnership is especially effective in smaller gardens where pest management is key. Just be sure not to overcrowd the soil, as both carrots and onions prefer loose, well-drained soil to develop properly.

2. Beets

Beets and onions coexist well in the same garden bed because they have different nutrient requirements and rooting depths. Onions have shallow roots, while beets grow deeper into the soil, which minimizes competition. Onions can also deter common beet pests such as leaf miners. Planting them together allows you to maximize garden space while reducing pest populations organically.

3. Lettuce

Lettuce grows quickly and thrives in the cooler, partially shaded microclimate that onions can help create. Onions provide a light canopy that can protect tender lettuce leaves from the hot sun, especially during late spring. In return, lettuce has shallow roots and grows fast, meaning it won’t crowd out onions and can be harvested well before onions mature. This is an excellent option for succession planting.

4. Strawberries

Strawberries benefit from being near onions because the pungent onion aroma repels aphids, slugs, and spider mites, which are common strawberry pests. Moreover, onions do not compete for the same root space, and their presence can help create a barrier against soil-borne pathogens. Many gardeners find this combination beneficial for keeping strawberries healthier and more productive throughout the season.

5. Spinach

Spinach, like lettuce, enjoys the cooler conditions onions help provide. These leafy greens can be tucked between rows of onions, benefiting from the subtle shade while helping to suppress weeds. Onions can also repel aphids and leaf miners that often attack spinach. As spinach matures quickly, it can be harvested multiple times before onions are ready, making efficient use of bed space.

6. Tomatoes

Though tomatoes and onions don’t share many similarities in appearance or growth habits, they can form a beneficial partnership. Onions help repel common tomato pests such as aphids and spider mites. However, it’s best to plant them at a slight distance rather than directly adjacent, as both are heavy feeders and may compete for nutrients if planted too closely. This combination works well when onions are planted along the edges of tomato beds.

7. Cabbage

Members of the cabbage family, including broccoli, kale, cauliflower, and Brussels sprouts, benefit from onion companionship. Onions emit sulfur compounds that deter many brassica pests such as cabbage worms, cabbage loopers, and aphids. The complementary growth patterns—onions growing tall and thin, cabbages forming wide heads—allow for efficient use of space. Consider interspersing onions throughout your cabbage patch to create a natural pest barrier.

8. Peppers

Peppers and onions can grow well together, especially in raised beds. While peppers need full sun, onions’ upright growth won’t block their light. Onions also help deter aphids and beetles that may target pepper plants. Their minimal root interference makes them excellent neighbors, especially when spacing is planned to ensure airflow and light access.

9. Chamomile

Chamomile is a fragrant herb that brings more than beauty to your onion bed. It can enhance the flavor and growth of onions through beneficial root interactions and attracting helpful insects like hoverflies and parasitic wasps. These insects prey on pests that would otherwise harm your onions. Chamomile is low-maintenance and makes a charming addition to any vegetable patch.

10. Dill

Dill, like chamomile, attracts beneficial insects such as ladybugs and lacewings, which feast on aphids and thrips—common onion pests. Planting dill near onions helps reduce the need for chemical interventions. However, keep in mind that dill can grow tall and may shade shorter plants. If you’re companion planting with dill, place it on the north side of the onion patch to avoid shading issues.

11. Marigolds

Marigolds are well-known in the companion planting world for their ability to repel nematodes, aphids, and other destructive pests. Their bold scent and bright blooms make them perfect companions for onions. When planted around the edges of onion beds, marigolds can help prevent soil-borne issues and act as a trap crop, attracting pests away from vegetables. Additionally, they enhance garden aesthetics.

12. Swiss Chard

Swiss chard and onions thrive under similar soil and light conditions, making them compatible garden mates. Their root systems don’t compete significantly, and onions may help deter leaf miners that occasionally target chard. The visual contrast between chard’s bold, colorful stems and the green, upright onion leaves can also add visual appeal to your garden design.

13. Celery

Celery and onions grow well together because they both prefer moist, fertile soils and consistent watering. Celery can benefit from onions’ natural pest-repelling properties, especially against aphids and slugs. In return, celery acts as a living mulch, helping retain soil moisture and suppress weeds around onion bulbs. This is a mutually beneficial pairing when space is optimized correctly.

14. Parsnips

Parsnips are another root crop that gets along well with onions. They’re less prone to pest attacks when grown near onions, which repel many harmful insects. Like carrots and beets, parsnips grow deeper into the soil, so they don’t interfere with onions’ shallower roots. Ensure both crops have ample space to avoid competition for nutrients and air circulation.

15 Summer Savory

Summer savory is a lesser-known but effective onion companion. It deters onion flies and improves the flavor of nearby vegetables. The aromatic herb attracts pollinators and beneficial insects, helping balance the ecosystem in your onion bed. Compact and bushy, summer savory fits well in garden borders or between rows, providing both pest control and culinary value.

Tips for Successful Onion Companion Planting

While these 16 plants are great companions, a few planting strategies can enhance their success:

• Spacing is Key: Avoid overcrowding. Each plant needs adequate airflow to reduce the risk of fungal infections, especially onions.
• Crop Rotation: Avoid planting onions in the same spot year after year to prevent soil-borne diseases. Rotate with leafy greens or legumes.
• Water Wisely: Companion plants with similar watering needs (like lettuce, spinach, and celery) are ideal. Avoid pairing onions with water-hungry crops that could drown them.
• Use Borders Strategically: Place pest-repelling herbs like chamomile, dill, and marigolds along garden edges to protect your crops without taking up valuable root space.
• Interplant with Purpose: Consider staggered planting schedules—fast growers like lettuce or spinach can be harvested before onions need full space.

Plants to Avoid Near Onions

While many plants get along with onions, some do not. Avoid planting onions near:

• Beans and Peas– These legumes may suffer stunted growth when grown near onions due to chemical interactions.
• Asparagus-Onions can inhibit asparagus growth and disrupt its long-term root development.
• Sage– Although aromatic, sage can struggle near onions due to competition and differing soil preferences.

Final Thoughts

Companion planting is more than just a gardening trend—it’s a sustainable, science-backed method for improving crop yields and protecting plants naturally. Onions, with their powerful pest-repelling properties and minimal soil requirements, make them ideal partners for a variety of fruits, vegetables, and herbs. By understanding the unique relationships onions have with other plants, you can cultivate a thriving, productive garden that’s as beautiful as it is bountiful. Grow above these  16 companion plants which suit your climate, soil, and space, and enjoy the rewards of a healthier, more balanced garden ecosystem. Happy Gardening….