Tradition
No chart mentions this pair.
Onion
Allium cepa
Amaryllidaceae
Tomato
Solanum lycopersicum
SolanaceaeCan you plant onions and tomatoes together?
Yes. Onions and tomatoes grow well together. Tomatoes yielded more next to onions in 3 studies, and onions improved the soil or nutrient uptake of tomatoes in 3 greenhouse or pot trials.
Why onions and tomatoes work together
Bigger combined harvest. In 3 studies, tomatoes yielded more next to onions.
Mechanisms of root exudates and soil microbial responses to nitrogen reduction and companion cropping for tomato yield increase and quality improvement. (Liu D · 2025 · Frontiers in plant science)and 2 more sourcesBetter soil and nutrient uptake. In 3 greenhouse or pot trials, onions improved the soil or nutrient uptake of tomatoes.
Intercropping with potato-onion alters arbuscular mycorrhizal fungi spore-associated bacterial communities of tomato rhizosphere. (Zhou L · 2025 · Frontiers in microbiology)and 2 more sourcesMixed results on soil and nutrients. In a greenhouse or pot trial, results on soil and nutrients were mixed.
Root separation modulates AMF diversity and composition in tomato-potato onion intercropping systems. (Ibrahim M · 2025 · Frontiers in microbiology)
What to plant with onions and tomatoes
Good neighbours of both, best tested first.
What to keep away from onions and tomatoes
The evidence in detail
For readers who want to dig in: every chart entry, study and yield trial behind the answer above, with the numbers.
Tradition, research and yield trials
Research
Good
avoidgood
7 papers found: 6 positive, 0 negative, 1 mixed.
nutrients / soil x4yield / land use x3
auto-classified not reviewed by a person
Yield trial
No intercropping yield trial.
Good neighbours
What happens above and below ground
Each animation illustrates a mechanism a study reported for this pair. Pick a card to focus on it.
Everything at once.
Companion plants for both onions and tomatoes
Plants that are good neighbours of each. Biggest harvest gain first; each cell links to the evidence for that pair.
| Plant | With onions | With tomatoes |
|---|---|---|
 Cabbage | Fewer pests and draws in pest-eating insects8% more harvest from the same spaceField trial, 8 studies. Charts: recommend.Evidence for onions and cabbage | 34% more harvest from the same spaceField trial, 4 studies. Charts: not listed.Evidence for tomatoes and cabbage |
 Cucumber | Helpful plant chemistry and bigger combined harvestField trial, 3 studies. Charts: recommend.Evidence for onions and cucumbers | Lures pests away17% more harvest from the same spaceField trial, 4 studies. Charts: recommend.Evidence for tomatoes and cucumbers |
 Leek | No trial foundSame family (Amaryllidaceae): shares pests and diseasesNot tested. Charts: recommend.Evidence for onions and leeks | Less disease and better soil and nutrient uptakeGreenhouse or pot trial, 2 studies. Charts: recommend.Evidence for tomatoes and leeks |
Harvest from the same space compares a bed with both crops against the same area split into single-crop beds, counting the harvest of both crops (the land equivalent ratio in yield trials).
Recommended by garden charts for both, not tested yet
The evidence, with sources
- Goodnutrients / soilgreenhouse / pot trialauto-classifiedOnion helps TomatoIntercropping with potato-onion alters arbuscular mycorrhizal fungi spore-associated bacterial communities of tomato rhizosphere.Intercropping with potato-onion alters arbuscular mycorrhizal fungi spore-associated bacterial communities of tomato rhizosphere. (Zhou L · 2025 · Frontiers in microbiology)Relevance 85% · effect confidence 55%
- Goodyield / land usegreenhouse / pot trialauto-classifiedOnion helps TomatoMechanisms of root exudates and soil microbial responses to nitrogen reduction and companion cropping for tomato yield increase and quality improvement.Mechanisms of root exudates and soil microbial responses to nitrogen reduction and companion cropping for tomato yield increase and quality improvement. (Liu D · 2025 · Frontiers in plant science)Relevance 89% · effect confidence 94%
- Goodyield / land usefield trialauto-classifiedOnion helps TomatoPotato-onion intercropping enhances tomato yield and quality and modifies soil microbial diversity.Potato-onion intercropping enhances tomato yield and quality and modifies soil microbial diversity. (He X · 2025 · Scientific reports)Relevance 94% · effect confidence 95%
Show 4 more
- Mixednutrients / soilgreenhouse / pot trialauto-classifiedRoot separation modulates AMF diversity and composition in tomato-potato onion intercropping systems.Root separation modulates AMF diversity and composition in tomato-potato onion intercropping systems. (Ibrahim M · 2025 · Frontiers in microbiology)Relevance 86% · effect confidence 30%
- Goodnutrients / soilgreenhouse / pot trialauto-classifiedOnion helps TomatoCommon mycorrhizal networks benefit to the asymmetric interspecific facilitation via K exchange in an agricultural intercropping systemCommon mycorrhizal networks benefit to the asymmetric interspecific facilitation via K exchange in an agricultural intercropping system (Gao D · 2021 · Biology and fertility of soils)Relevance 81% · effect confidence 50%
- Goodyield / land usegreenhouse / pot trialauto-classifiedOnion helps TomatoBiochar and Intercropping With Potato-Onion Enhanced the Growth and Yield Advantages of Tomato by Regulating the Soil Properties, Nutrient Uptake, and Soil Microbial Community.Biochar and Intercropping With Potato-Onion Enhanced the Growth and Yield Advantages of Tomato by Regulating the Soil Properties, Nutrient Uptake, and Soil Microbial Community. (He X · 2021 · Frontiers in microbiology)Relevance 89% · effect confidence 85%
- Goodnutrients / soilgreenhouse / pot trialauto-classifiedOnion helps TomatoIntercropping with Potato-Onion Enhanced the Soil Microbial Diversity of Tomato.Intercropping with Potato-Onion Enhanced the Soil Microbial Diversity of Tomato. (Li N · 2020 · Microorganisms)Relevance 91% · effect confidence 91%
All neighbours of onion and of tomato, or every pair at once in the companion planting chart.
Have you grown onions and tomatoes together?
Tell other gardeners what happened: spacing, pests, harvest, or ask a question. Reader notes are not checked by us and do not change the verdicts on this page.