Companion Plant Guide
Carrot
Pest-confusion pairing — each hides the other from its fly.
Vegetable · Allium family
Onion companion plants
Allium cepa
What to plant with onions, what to keep apart, and how to grow them — sun, spacing, soil and the reason behind every pairing.
Photo: Lars Blankers on Unsplash
Overview
Growing onions beside the right neighbour
Onion (Allium cepa) is a vegetable in the Allium family. Bulb crop that stores well and repels many pests.
Onions ask little of the soil, so they slot neatly into gaps between hungrier crops.
Give plants 4–6 in in full sun. Aim for well-draining, fertile soil. In most gardens the crop sits in USDA zones 3-10 and is ready in about 100-120 days.
Grows well with
What to plant with onions
The best companion plants for onions in this guide are Carrot, Lettuce, Pepper, Beet, Tomato, Cabbage, Broccoli, and Strawberry. Each pairing below is a reason to share a bed — pest masking, roots that do not compete, or insects that hunt the pests drawn to onions.
Lettuce
Pest deterrent for lettuce.
Pepper
Pest deterrent and space efficient.
Beet
Different root depths; onions help deter beet pests.
Tomato
Strong scent helps mask tomatoes from aphids.
Cabbage
Strong scent helps hide brassicas from cabbage moths.
Broccoli
Strong scent helps hide brassicas from cabbage moths.
Strawberry
Strong scent is said to keep pests off the fruit.
Keep apart
What not to plant with onions
Keep onions away from Bean, Asparagus, and Pea. These neighbours compete for the same food, release chemicals that stunt growth, or otherwise hold the crop back.
Bean
Alliums stunt beans and slow nitrogen fixation.
Asparagus
Alliums are said to stunt asparagus crowns.
Pea
Alliums stunt peas and slow nitrogen fixation.
In the bed
How to grow onions
| Sun | Full sun |
|---|---|
| Spacing | 4–6 in |
| Soil | Well-draining, fertile soil |
| Hardiness | Zones 3-10 |
| Days to maturity | 100-120 |
These notes sit beside the companion lists — they are how onion actually occupies the bed, not a substitute for local climate.
- Plant sets in spring or fall for best results
- Thin to proper spacing for good bulb formation
- Stop watering when tops fall over
- Cure bulbs in warm, dry place before storage
Questions
Onion companion planting FAQ
What can I plant next to onions?
Plant Carrot, Lettuce, Pepper, Beet, Tomato, Cabbage, Broccoli, and Strawberry beside onions. Carrot: Pest-confusion pairing — each hides the other from its fly. Lettuce: Pest deterrent for lettuce. Pepper: Pest deterrent and space efficient. Beet: Different root depths; onions help deter beet pests. Tomato: Strong scent helps mask tomatoes from aphids. Cabbage: Strong scent helps hide brassicas from cabbage moths. Broccoli: Strong scent helps hide brassicas from cabbage moths. Strawberry: Strong scent is said to keep pests off the fruit.
What should I not plant with onions?
Keep onions apart from Bean, Asparagus, and Pea. Bean: Alliums stunt beans and slow nitrogen fixation. Asparagus: Alliums are said to stunt asparagus crowns. Pea: Alliums stunt peas and slow nitrogen fixation.
How much sun do onion plants need?
Onion plants want full sun. Space them 4–6 in apart in well-draining, fertile soil.
How long do onion plants take to mature?
Most onion plants are ready in about 100-120 days. Onion grows in USDA hardiness zones 3-10.
Compare every pairing at a glance
Open the guide, pick onion, and see what thrives alongside it — and what quietly holds it back.
Open the pairing guide