Onion (Allium cepa)

Allium FamilyHerbsRootsVegetables

Onions benefit from companion planting by forming mutually supportive relationships with certain crops. Vegetables like carrots, beets, lettuce, and spinach help repel pests such as onion flies and thrips. Carrots, in particular, contribute to pest control while also helping conserve soil moisture and provide shade.

However, some plants, like garlic and chives, should be avoided as onion companions since they compete for nutrients and attract similar pests. By strategically pairing onions with beneficial plants and avoiding unfavorable ones, gardeners can enhance biodiversity, attract pollinators, and create a more balanced, self-sustaining garden.

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14 Companion Plants for Onion

• Carrot Onions can help repel the dreaded carrot fly. By surrounding your carrot crop with onions, you can keep the garden pest from destroying your carrot harvest.
• Lettuce Some lettuce varieties are ideal companions for onions because they can be grown as a cover crop
• Cabbage Cabbage is a great companion plant for onions, as onions help repel common cabbage pests like cabbage worms and aphids. In return, cabbage provides ground cover, helping to retain soil moisture.
• Dill Dill is beneficial for enhancing the flavor and growth of onions. Additionally, dill attracts beneficial insects like wasps and hoverflies, which prey on pests that may damage onion crops.
• Brassicas Any crop in the cabbage family, such as broccoli, cabbages, cauliflower, kale, collards, mustard, and kohlrabi is beneficial to onions. These plants will keep unwanted pests away from onions and help enhance flavor.
• Radish Radish is a beneficial companion plant for onions, as it helps break up compacted soil, allowing onions to grow more easily. Additionally, radishes can attract pests like flea beetles away from onions, serving as a natural trap crop.
• Beet Beets share similar growing conditions with onions, so they grow well together. Additionally, beets help improve soil structure and act as a ground cover, shading the soil and reducing moisture loss.
• Basil Basil is a culinary companion to onions, as it can enhance their flavor when planted close by.
• Rosemary Rosemary is an excellent companion plant for onions because its strong aroma helps deter pests like onion flies and aphids. It also attracts beneficial insects that contribute to a healthier garden ecosystem.
• Thyme Thyme is a great companion for onions, repelling pests like onion flies while attracting beneficial insects. Its low growth helps retain moisture and suppress weeds without competing for nutrients.
• Celery Celery is a good companion for onions, as onions help deter pests that commonly attack celery. In return, celery’s foliage provides light shade, helping to retain soil moisture and create a balanced growing environment.
• Parsnip Another root crop that can work well alongside onions are parsnips. They can grow happily alongside one another and can also help in pest control.
• Tomatoes Onions help repel pests like aphids, spider mites, and hornworms, which can commonly affect tomatoes. In return, tomatoes can provide some shade to onions, helping to protect them from the intense midday sun.
• Cucumbers Cucumbers can be a good companion for onions. The strong smell of onions helps deter pests like aphids and cucumber beetles that can harm cucumbers.

8 Neighbor Plants to Avoid near Onion

• Asparagus The growth of both onions and asparagus will be inhibited when they're grown next to one another because they compete for the same nutrients.
• Turnip Turnips are good companions for onions as they don’t compete for nutrients and help break up the soil. They also help deter pests, benefiting onion growth.
• Peas Peas are not ideal companions for onions. Onions can inhibit pea growth by competing for nutrients, and the strong scent of onions may interfere with the peas’ development. It’s best to plant them separately.
• Beans Beans are also not good companions for onions. Onions can stunt bean growth by competing for nutrients, and their strong odor can affect the beans’ development. It’s best to avoid planting them together.
• Garlic Although garlic is a close relative of onions, planting them together may increase the risk of cross-contamination with diseases and pest.
• Sage This herb produces allelopathic compounds that can inhibit the growth of nearby plants, including onions.
• Corn Corn is generally not considered an ideal companion plant for onions. Both plants have different growth habits, and corn tends to grow tall, potentially shading onions and limiting their access to sunlight.
• Mint Mint is not a good companion plant for onions. Mint tends to spread aggressively, which can crowd out onions and other nearby plants.