10 Best Onion Companion Plants

Companion planting is an age-old practice that pairs plants together in the garden to provide some benefit to one or both partners. Companion plants play various roles in the vegetable garden community. Onions produce strong odors in the form of volatile compounds that can confuse and deter plant pests. Planting onions with companion plants is a great way to manage insect pests on carrots, peppers, and other vegetable crops. Onion companion plants provide similar benefits to onions, helping to attract beneficial insects and reduce pest pressure. Some herbs are even rumored to improve the flavor of onions when grown in close proximity.

Scattering onion plants among companions throughout the garden is a great way to reduce pressure from one of the most common pests, onion maggots. This pest burrows into the developing roots and easily moves from plant to plant when onions are set in a row. Break your onion plantings into small groups tucked among herbs, vegetables, and other plants that benefit from the pairing. Onions perform best in rich, well-drained soil and full sun, though some species, such as chives, also tolerate partial shade. Pair onions with plants that thrive under similar growing conditions. Plant onions in fall or very early spring, as soon as the soil can be worked.

01 of 10

Peppers

Pepper plant in the garden — Getty Images

Botanical Name: Capsicum annuum
Planting Time: Late spring, after the threat of frost has passed

Studies have demonstrated the benefit onions provide to peppers when planted together in the garden. The scent of onions protects peppers against attack by the green peach aphids, a damaging pest that feeds on foliage and transmits several viruses to pepper plants.

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Cabbage

Botanical Name: Brassica oleracea
Planting Time: Early spring, as soon as soil can be worked

Cabbage is another crop that benefits from the aromatic compounds emitted by onions. Research has shown onions interplanted between cabbage reduced cabbage looper and imported cabbage worms, two pests that feed on the foliage as caterpillars. Other members of the cabbage family, including broccoli and Chinese cabbage, also benefit from the pairing. In Chinese cabbage, green onions help deter flea beetles. For the best results, plant onions two weeks before planting cabbage.

03 of 10

Tomato

Botanical Name: Solanum lycopersicum
Planting Time: Late spring, after the threat of frost has passed

Tomatoes grown alongside potato onions and chives have demonstrated resistance against certain plant diseases. When planted with potato onions, tomatoes show enhanced resistance to Fusarium wilt, likely due to increased anti-fungal enzyme activity in the soil. Likewise, Chinese chives suppress bacterial wilt of tomato plants when grown together.

04 of 10

Carrots

Botanical Name: Daucus carota subsp. sativus
Planting Time: Mid Spring or Fall

Onions are known to repel carrot flies, a common carrot pest. The larvae of carrot flies, called maggots, feed on the roots of carrots and closely related plants. Onions benefit in return through reduced incidence of thrips which commonly attack young onion leaves. The presence of beneficial beetle predators is also higher among intercropped plantings. Young onions provide carrots with better protection than older, bulb-forming plants.

05 of 10

Beets

Beet greens are green leaves with purple veins growing from a root crop in the ground — Getty Images / Fotomary

Botanical Name: Beta vulgaris subsp. vulgaris
Planting Time: Early spring or Fall

Beets and onions require similar soil conditions for optimal growth and studies show that intercropping increases the yield of both species and reduces root knot nematodes in beets. These studies were conducted using sugar beets, which are a different variety but the same species as garden beets.

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Summer Savory

Botanical Name: Satureja hortensis
Planting Time: Start seed indoors 6 weeks before last frost date

A number of herbs thrive alongside onions thanks to their similar growing requirements. Among these is summer savory, which many gardeners believe helps to improve the flavor of onions when grown together.

07 of 10

Chamomile

A lot of camomile flowers — Getty Images

Botanical Name: Matricaria recutita
Planting Time: Start seed indoors 4-6 weeks before last frost date

Chamomile is another herb believed to improve the flavor of onions when planted together in the garden. Chamomile has similar cultural needs as onions, including full sun and rich, well-drained soils.

08 of 10

Rue

Common rue - Latin name - Ruta graveolens — Getty Images

Botanical Name: Ruta graveolens
Planting Time: Start seed indoors 6-7 weeks before last frost date

Once widely planted in the herb garden, rue has fallen out of popularity, but this drought-tolerant herb provides many benefits. It serves as a host plant to larvae of black swallowtail, giant swallowtail, and other butterflies, and is resistant to deer browsing. If you’ve ever crushed the foliage of rue, you are familiar with its pungent odor. The scent deters aphids, flea beetles, and onion maggots.

09 of 10

Strawberry

Red ripe strawberries growing in garden — Getty Images

Botanical Name: Fragaria × ananassa
Planting Time: Early Spring or Fall

Though research is limited, garden observations suggest planting strawberries with onions helps ward off strawberry diseases. Additionally, strawberries grown as a groundcover around onions help to shade soils, which keeps temperatures more moderate and helps to retain soil moisture, both of which benefit onion plants.

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Roses

Botanical Name: Rosa spp.
Planting Time: Late spring, after the threat of frost has passed

Ornamental onions, garlic, chives, and edible onions are often planted with roses to ward off aphids and protect plants against black spot disease. Many rose growers believe that this pairing also increases the amount of fragrance roses give off. The flowering ornamental onions pair beautifully with roses, complementing most flower colors.

Plants Not To Plant With Onions

Some plants do not make good neighbors in the garden. For example, it is believed that onions stunt the growth of pea and bean plants. It is best to keep these plants apart. Also avoid planting onions near asparagus, as the two plants compete for similar nutrients in the soil.

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