Free Growli tool
Companion plant finder
— top companions in 1 click.
Pick any of 12 common vegetable crops and the finder returns its top five companion plants and up to three antagonists to keep at a distance. Every pairing carries an evidence tag — strong, moderate, or traditional — drawn from peer-reviewed studies, US cooperative extension, and the RHS.
Twelve common vegetable garden crops. Every pairing is cross-checked against peer-reviewed studies, US cooperative extension publications, and RHS guidance.
Companion plan for tomatoes
Tomatoes: top 5 companions, 2 to avoid
Heavy feeder, warm-season, prone to early and late blight. Hosts hornworms, aphids, and whiteflies. Self-pollinating but produces more fruit when pollinator activity is high.
Top companions
- BasilStrong evidence
A 2024 study in Plant Cell Reports identified three basil volatiles (linalool, chavicol, alpha-terpineol) that prime tomato wound-defence genes — caterpillars on primed plants gained roughly half the weight of controls. West Virginia University intercropping trials also recorded ~20% yield gains.
- PeppersModerate evidence
Same warm-season window, soil pH, and light demand — they share growing conditions, so a single bed plan works for both. Rotate the whole nightshade group every 2-3 years to limit shared disease pressure.
- GarlicModerate evidence
Allium sulfur compounds (allicin) have been shown to suppress aphid populations and spider mites in adjacent crops. Plant garlic 12-18 inches from tomato roots so the alliums do not interfere with the tomato's nitrogen uptake.
- OnionsModerate evidence
Same allium effect as garlic — strong-scented foliage masks tomato volatiles that aphids and whiteflies use to find their host. Onions are shallow-rooted so they don't compete heavily with tomato roots.
- LettuceModerate evidence
Lettuce uses the shaded ground beneath maturing tomato vines, extending the lettuce season into early summer before heat triggers bolting. Lettuce also acts as a living mulch, keeping soil moisture even.
Plants to keep at a distance
- Bush beansTraditional pairing
Bush beans are technically tolerable neighbours, but most extension services recommend keeping legumes a few rows away from tomatoes because the heavy feeding habit of tomatoes can outcompete bean roots for water in dry weeks. Not a hard incompatibility — more a practical spacing issue.
- PeasModerate evidence
Peas finish their cycle just as tomatoes ramp up, so they rarely compete in time — but in the overlap, tomatoes shade peas excessively and peas can spread powdery mildew that also affects tomatoes. Separate beds is the safer call.
Why this works
Good companions share a bed without competing for the same root zone, water, or nutrients — and often deliver an active benefit (pest scent masking, nitrogen fixing, shade cover, trap-cropping). Bad pairings either fight for the same resources or release chemistry that suppresses the other crop. For tomatoes, the strongest gains come from neighbours that target the pests in its profile and time their growth around its peak season.
Use the full pairings page linked above for spacing notes, planting timing, and the science behind each pair. The Growli app builds your full bed layout from your crop list automatically.
Save this layout to your garden
The Growli app remembers every crop you plant and flags companion and antagonist conflicts before you sow. It also rotates the bed plan each season so nightshades and brassicas don't hit the same soil twice in a row.
Save to Growli →How companion planting actually works
Companion planting earns its keep in three concrete ways. First, pest scent masking — alliums (onions, garlic) release sulfur volatiles that confuse carrot fly, aphids, and spider mites; basil volatiles disrupt thrips and whiteflies. Second, resource sharing — legumes (peas, bush beans) fix nitrogen that heavy feeders like cucumbers and lettuce immediately use, while shallow-rooted lettuce shares beds with deep-rooted carrots without competing.
Third, trap cropping — radishes draw cucumber beetles and leafminers onto themselves so the cucumbers or spinach escape damage. Each of these effects has been measured in peer-reviewed studies or replicated extension trials, which is why the finder tags pairings as strong, moderate, or traditional.
What this tool does not capture. Your specific climate, soil type, irrigation regime, or which pests are actually active in your garden this season. For the full bed layout — companions, rotation, spacing, and pest-pressure adjustments — the Growli app builds it from your crop list automatically.
Frequently asked questions
What is companion planting?
Companion planting is the practice of placing different crops next to each other so they help — or at least do not hinder — each other in the same bed. Good companions can repel pests through scent, fix nitrogen for heavy feeders, provide shade or living mulch, or trap pests away from the main crop. Bad pairings compete for water, nutrients, or root space, or release chemistry that suppresses the neighbour.
Are these pairings backed by science or folklore?
A mix. Each pairing in the finder carries an evidence tag: Strong means peer-reviewed or replicated extension trials (basil prompting tomato defence genes, radishes as cucumber-beetle trap crop, onions reducing carrot fly egg-laying). Moderate means single peer-reviewed studies or strong extension consensus. Traditional means long-standing gardener practice with limited formal evidence — useful, but treat it as practice rather than a guaranteed effect.
How close should companion plants be to each other?
Most companion effects need the plants to share the same bed — typically within 12 to 24 inches of each other so the volatile chemistry, root zone, and shade cover actually overlap. The exception is trap-cropping (like radishes for cucumber beetles), which works in the same bed but does not need to be inches-close. Antagonist pairs should stay at least 2 to 3 rows or roughly 3 feet apart.
What is the worst companion-planting mistake?
Putting alliums (onions, garlic) next to legumes (peas, bush beans). Alliums release sulfur compounds that suppress the Rhizobium bacteria the legumes rely on for nitrogen fixation. Multiple extension services confirm measurable yield drops on the legume side. Other classic mistakes: aromatic herbs near cucumbers (flavour taint), and crowding the bed so any nominal companion benefit gets cancelled by spacing competition.
Do I need to rotate companion-planted beds?
Yes — companion planting and crop rotation work together, not as substitutes. Even the best companion pairing builds up soil-borne disease pressure (Verticillium, Fusarium, club root) if the same family stays in the same bed year after year. Rotate the whole nightshade block (tomatoes, peppers), the brassicas, and the alliums every 2 to 3 years.
How is this different from the Growli app?
The finder gives you the top companions and antagonists for one crop at a time. The Growli app lays out your whole bed from your crop list — flagging companion wins, antagonist conflicts, and rotation issues before you plant — and adjusts the plan each season as you swap crops in and out.