Onion

Asparagus

Onions are said to deter some asparagus pests.

Cabbage

Onions can help deter cabbage worms and other brassica pests.

Summer savory

Can be planted near onions to deter onion thrips.

Winter savory

Enhances growth and flavor.

Parsnip

Onions are said to deter carrot rust flies, which also affect parsnips.

Carrot

Onions are said to deter carrot rust flies.

Salad rocket

Onions are said to deter some pests of rocket.

Celery celeriac

Onions are said to deter some celery pests.

Beetroot chard

Onions are good companions for beets.

Swede rapeseed

Onions are said to deter some brassica pests.

Brussels sprouts

Onions are said to deter some pests of Brassicas.

Broccoli

Onions are said to deter some pests of broccoli.

Turnip

Onions are said to deter root maggots and aphids from turnips.

Pepper

Onions can help deter some pests from peppers.

German chamomile

Reported to improve growth and flavor of onions.