6 Onion Plant Companion Plants

Onions are delicious and low-maintenance plants. What companion plants should you grow next to them?

Onions are delicious, versatile, low-maintenance plants and excellent for companion planting. Many plants benefit from them as a natural insect deterrent, and they are also said to enhance the flavor of neighboring crops. 

Discover which vegetables, herbs, and flowers make good companions to your onion plant.

1. Brassicas

Brassica plants such as broccoli, kale, cauliflower, turnips, kohlrabi, and brussels sprouts thrive when cultivated alongside onions because the onions repel most pests that attack cabbage crops. 

Onions also deter insects, such as cabbage worms, loopers, and larvae, which feed on the brassicas.

brussels sprout plant in the garden

2. Tomato

Onions and other alliums make excellent companion plants for tomatoes and other nightshade plants. The pungent onion scent masks the aroma of tomatoes, so insects are less likely to feed on the fruits.

Onions repel spider mites, so growing tomatoes, peppers, and onions together benefit all three crops. 

ready to harvest tomato in the garden

3. Strawberry

Strawberries are likely to be attacked by pests, like aphids, making them more vulnerable to disease and damage. Thankfully, aphids and sap-sucking pests are easily repelled by the onions.

The onions help protect the strawberry crop from insects and other pests, increasing the quality and yield of your harvest. Both plants also thrive on well-drained soil and grow in similar conditions.

ripe strawberry in the garden

4. Carrots

Carrots and onions do not compete for nutrition. Both plants thrive together effectively since they grow at different levels in the soil. The onion bulb collects water from the top few inches of soil, whereas the carrot sends its taproot deep into the soil.

The scent of the onion also repels the carrot fly, a common pest of carrots, and other bug species like aphids and flea beetles.

5. Swiss Chard

Swiss chard can be cultivated alongside most allium plants for mutual benefit. The broad leaves of swiss chard can block sunlight, helping keep the soil moist, which is good for the growth of the short-rooted onion.

Onions attract beneficial insects and keep pests at bay. Keep in mind that the swiss chard has spreading growth as it matures, so make sure it does not crowd out your onion crops as the bulbs are developing.

broad leaves of swiss chard

6. Herbs

Herbs like savory, marjoram, rosemary, and dill are helpful companion plants to onions. Other herbs like chamomile have antifungal qualities, which benefit the onions growing in humid climates. 

Planting mint near onions can deter onion flies, but mint can quickly crowd out other plants in the garden. Ensure the herbs do not take over your crop’s space. 

Some herbs like chives are not ideal for companion planting because both plants are alliums and have common diseases and pests.

Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
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