PlantWise

Companion plants for onions

What to grow next to onions, what to keep away from them, and why. Each reason is tagged by how well it’s supported.

Good companions

  • Carrots Garden tradition

    Traditional pairing; mixed rows may confuse carrot fly and onion fly.

  • Lettuce Practical reason

    Fits between rows while onions are young.

  • Tomatoes and peppers Practical reason

    Compact onions fill space around them.

Keep apart

  • Beans Garden tradition

    Traditionally said to be stunted by alliums.

  • Peas Garden tradition

    Same allium tradition.

Planning the bed

Space onions 4 inches apart (9 per square foot in square-foot gardening); the spacing calculator works out how many fit. For timing, see when to plant onions, and the full companion planting chart compares all 16 vegetables at once.

Questions gardeners ask

What are the best companion plants for onions?

Carrots, Lettuce, Tomatoes and peppers. Carrots: Traditional pairing; mixed rows may confuse carrot fly and onion fly.

What should you not plant with onions?

Beans, Peas. Beans: Traditionally said to be stunted by alliums.