Herbs are a common subject of companion planting lore: gardeners trade lists claiming certain herbs will ward off pests, boost flavors, or be "good friends" with specific crops. The scientific record for most of these claims is thin; many come from tradition or small-scale anecdotes rather than replicated trials. That said, some practices tied to herbs do have plausible mechanisms — for example, planting bloom-bearing herbs to attract pollinators or avoiding aggressive spreaders that compete with neighbors. Treat specific herb pairings skeptically and prioritize light, spacing, soil health, and overall bed diversity.
Most companion planting claims are based on anecdotal evidence, not rigorous science. We focus on what reliably works: plant placement by height relative to sun, proper spacing, organic soil amendments, and garden diversity.
The number of rigorous scientific studies regarding companion planting is small compared to the number of books, lists, and charts about companion planting based on anecdotal evidence.
— UMass Amherst Center for Agriculture, Food, and the Environment. See also Montana State University Extension.
| Plant | Claim | Evidence | Notes |
|---|---|---|---|
| Basil + Tomatoes | Basil improves tomato flavor and repels tomato pests. | Folklore | Flavor and pest-repellent claims are mostly anecdotal and not supported by rigorous trials. Planting basil near tomatoes is fine for space and pollinator attraction, but any flavor effect is unproven. |
| Mint + Brassicas (cabbage family) | Mint planted nearby will repel cabbage moths and other brassica pests. | Folklore | There is little controlled evidence that mint planted in the ground repels specific pests from neighboring crops. Mint's main practical problem is aggressive spreading and competition; keep it in containers if you don't want crowding. |
| Chives/Alliums + Roses or Fruit Trees | Chives prevent fungal diseases such as black spot on roses or improve fruit tree health. | Folklore | Claims that alliums act as broad fungicides or protect nearby plants are anecdotal. While garlic or chive extracts can show activity in lab tests, field-level protective effects from simple companion planting are not well documented. |
| Borage + Tomatoes/Strawberries | Borage increases pollination and yield for nearby strawberries or tomatoes. | Limited evidence | Borage attracts bees and other pollinators, which can increase pollination service for nearby flowering crops. Evidence on consistent yield gains is mixed and context-dependent, but the pollinator mechanism is plausible and supported by observational studies. |
| Tagetes (Marigold) roots tilled in | Tilling marigold roots into soil suppresses certain root-knot nematodes. | Supported | Studies and extension guidance show that specific marigold species, when used as a cover crop and incorporated into the soil, can reduce some nematode populations. Planting marigolds nearby without incorporation does not reliably give the same effect. |
| Mixed herbs interplanted in a bed | Mixing several different herbs reduces pest outbreaks compared to a single-species patch. | Supported | General research on crop diversity shows that mixing unrelated plants can reduce pest buildup by breaking host continuity and supporting natural enemies. This is a landscape/ecology effect rather than a magic pairing specific to particular herb species. |
| Fennel + Most garden plants | Fennel grows well next to most plants; they are good companions. | Limited evidence | Fennel produces strong-smelling compounds and can inhibit germination or growth of some nearby seedlings in small studies and many gardener reports. Evidence is mixed, so many extensions advise planting fennel away from small, sensitive crops. |
| Thyme/Oregano as groundcover under shrubs | Thyme or oregano planted under other plants will keep pests away and boost growth. | Folklore | Aromatic groundcovers may alter microclimate or deter some insects in limited cases, but broad claims about pest control or growth enhancement are not backed by replicated field trials. Their main effects are groundcover and weed suppression, not reliable pest repellency. |
| Basil + Peppers | Basil next to peppers reduces aphids and boosts pepper health. | Folklore | No consistent trial evidence shows basil reliably repels aphids or improves pepper yields. Observations of lower pest pressure are likely due to surrounding plant diversity or other garden conditions, not a basil-specific chemical shield. |
For herbs, apply the same practical rules that work across vegetable gardens: place tall or vining herbs (e.g., dill, tansy when tall) on the north or east side so they don't shade shorter plants; give spreading herbs like mint or oregano room or grow them in pots to avoid root competition; top-dress beds with compost before planting herbs each year to maintain soil biology; and interplant several different herbs and flowers to support pollinators and natural enemies rather than relying on single "repellent" plants.
Stop guessing at plant pairings. Our garden planner optimizes your layout based on plant height, sun direction, spacing, and your local frost dates — the things that actually make a difference.
Claims that basil changes tomato flavor come from anecdote rather than controlled experiments. If you like having basil nearby, plant it for convenience and pollinator visits, but don’t expect a reproducible flavor boost backed by science.
There are few replicated trials showing that simply planting aromatic herbs nearby repels specific pests from another crop. In many cases any observed reduction is better explained by increased habitat for predators or by chance; avoid depending on herbs alone for pest control.
Extension research shows marigolds can suppress some nematodes when grown as a cover crop and incorporated into the soil. Planting marigolds adjacent to herbs without tilling the roots in is unlikely to give reliable nematode control.
Aggressive spreaders like mint can crowd and outcompete neighbors, so give them containers or barriers. Fennel is often reported to inhibit some seedlings, so many gardeners keep it isolated; these are practical crowding and chemical-interference cautions rather than universal prohibition.