What to plant next to Onion

The neighbours on this page are sorted by what the evidence shows: a proven benefit, good with a condition, simply compatible, or to keep apart. Each group says why, and the sources are listed at the end of the page.

Good neighbours, with a condition

A tall or climbing plant shades a low plant that needs full sun, so put the tall one on the north side (the south side in the southern hemisphere).

These go on the north side, this plant on the south:

Compatible

They grow together without a known conflict, but the benefits traditionally claimed for these pairings are not proven.

Why it helps

Mixing crops in the same bed spreads the risk: pests find their target harder, the soil is used at different depths and flowers bring in the insects that pollinate and hunt aphids.

Spacing in the row	10 cm (3.9 in)
In a 30 cm (1 ft) square	16 per square
Crop rotation group	Roots and onions
Sow outdoors	Mar–Apr
Harvest	Jul–Aug

Onion: spacing, plants per square and companions →

Plan it in the garden

The planner warns you when two crops with a documented shared risk, such as tomatoes and potatoes, end up next to each other, so you can fix the layout before planting.

Start Planning Your Garden

Sources

The class of each neighbour on this page rests on these sources.

The Myth of Companion Plantings (L. Chalker-Scott) — Washington State University Extension for: compatible; checked 2026-10-28
Planning the Vegetable Garden (426-312) — Virginia Cooperative Extension, Virginia Tech for: good neighbours, with a condition; checked 2026-10-31
Preparing a garden plan — UC Master Gardener Program, UC ANR for: good neighbours, with a condition; checked 2026-10-31