PlantAlong

What to plant with onions

Sources list Carrots, Tomatoes and Lettuce as good companions for onions. Keep onions apart from Beans and Peas. Only one pairing has been tested in a study; the rest are guidance or tradition.

Pairings
5
Last reviewed
Photo: Halimatu Sa'diah - Koruch / Pexels
Good neighbors first, then plants to keep apart. Each one says how strong the evidence is.

Helps

  • Carrots Tested in a study

    Intercropped onions reduced carrot fly (Psila rosae) attack on carrots, probably because onion volatiles disrupt host finding; onion thrips on the onions were also reduced.123

    Conditions (Uvah & Coaker 1984, abstract only): effect greatest with young onions and higher onion:carrot plant density ratios, and virtually ineffective once onions began to bulb. Matters only where carrot fly is a pest. WSU EM128E separately advises pairing taproot carrots with shallow-rooted onions to limit root competition (guidance, no study cited for this pair).

  • Tomatoes Traditional pairing3

    The chart says "onion family".

  • Lettuce Traditional pairing3

Keep apart

  • Beans Traditional pairing3

  • Peas Traditional pairing3

Traditional pairings come from a UC Master Gardener chart that traces to the UC Davis Edible Landscaping Handbook and ATTRA. The chart gives no reasons, and we found no trial of these pairs; treat them as garden lore.

Sources

  1. Entomologia Experimentalis et Applicata 36(2):159-167 (John Wiley & Sons); abstract read via FAO AGRIS, Effect of mixed cropping on some insect pests of carrots and onions, 1984. Retrieved 2026-11-02.
  2. Washington State University Extension, Gardening with Companion Plants (Home Garden Series), EM128E, December 2023. Retrieved 2026-11-02.
  3. University of California Agriculture and Natural Resources (UCCE Master Gardener Program), Companion Planting Chart: Companion planting in the vegetable garden, File dated 2023-09 in URL path; no date printed. Retrieved 2026-11-02.