Can You Plant Tomatoes With Onions?
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GardenSays
Tomatoes + onions: Yes — plant them together.
- Verdict
- Good companions
- Evidence
- Traditional
- Pairs rated
- 41
Alliums' strong scent is traditionally credited with deterring aphids and some beetles, and onions occupy little root or air space, so there's no competition cost either way.
Layout: Plant onion sets in a row along the bed edge, 6-12 inches from tomato stems.
Why
- ✓This is long-standing garden practice; the mechanism is plausible but hasn't been formally tested.
- ✓Companion planting tweaks the odds — spacing, rotation, and airflow still matter more than any pairing.
When this doesn't apply
- →If either plant has had disease problems in this spot before, rotation history outweighs the pairing benefit.
How this was calculated
- 1. Pairing lookupGood companions
Tomato × Onions: rated 'good' (traditional) in the GardenSays pairing table.
- 2. Evidence standard
Confidence labels: 'documented' = mechanism supported in extension/research literature; 'traditional' = long-standing practice with plausible mechanism but thin formal evidence.
Data sources
- University of Minnesota Extension — Companion planting in home gardens — Some companion effects (trap crops, pollinator attraction, nematode suppression by marigolds) are documented; many traditional pairings lack formal evidence. (checked 2026-07-15)
- University of Minnesota Extension — Growing tomatoes in home gardens — Avoid planting tomatoes near potatoes (shared blight) or where related crops grew the previous year. (checked 2026-07-15)
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