Pick a crop above and you get two lists: what to plant near it, and what to keep away. Every entry carries a reason and a label saying how well that reason is actually supported.
The label is the point. Most companion planting charts are a grid of names with no indication that some pairings rest on studied mechanisms and most rest on nothing at all.
What the three labels mean
Supported — a mechanism that has been studied and holds up. There are only a few, and they are worth planning a bed around:
- Feeding beneficial insects. Small, shallow, open flowers — the umbels of dill, cilantro and parsley, and the flowers of oregano and thyme — are accessible to hoverflies, parasitic wasps and lacewings, whose larvae eat aphids and caterpillars. The catch, which almost every chart omits: it only works from a plant in flower. A patch clipped for the kitchen all season feeds nobody.
- Nematode suppression by marigolds. Real, and specific: it needs a dense stand grown across the ground for a season and then dug in, effectively as a cover crop. A few marigolds dotted between tomatoes will not do it.
- Shared pests within a family. Two plants in the same botanical family host the same pests and diseases. This is the strongest reason to keep two crops apart, and it is why rotation is organised by family rather than by crop.
- Incompatible watering. Not a pest question at all. A woody Mediterranean herb wants poor, sharply drained soil kept dry; a leafy or fruiting vegetable wants steady moisture and feeding. Whichever regime you follow, one of them suffers. This is the most reliably useful thing on the chart and almost nobody publishes it.
Plausible — a mechanism that makes sense and has little or no testing behind it. Scent masking is the main one: aromatic herbs near brassicas, said to confuse cabbage moth. It costs nothing to try. Nitrogen fixing sits here too, for a reason worth knowing — beans and peas do fix their own nitrogen, but they keep most of it until the plant is dug in, so the crop that follows benefits more than the neighbour standing beside it.
Tradition only — repeated in garden lore with no mechanism worth citing. About two thirds of all the pairings on this chart fall here.
Why we show the weak pairings instead of dropping them
A chart of only the well-supported pairings would be short, honest and useless, because a reader who has met a claim elsewhere and cannot find it here will assume we missed it rather than that we checked. So the traditional claims stay, labelled.
This is the same treatment the marigold-and-beans claim got on our own data. Marigolds were once listed as inhibiting beans, a claim repeated widely and supported nowhere; rather than leave it unmarked or silently delete it, we established it was folklore and removed it from the data with the reasoning recorded. Does companion planting actually work goes through the five mechanisms in detail and is the longer read behind this chart.
How this chart is built
Every row is generated from the companion lists on our crop guides, read directly from the same data file those pages use. Nothing here is typed out by hand, which means the chart cannot drift away from the guides — a hand-maintained grid of 28 crops would be several hundred cells, and every hand-maintained figure in this project has eventually disagreed with its source.
The reasons are derived too, rather than written per pair:
- Botanical family gives the shared-pest reason, in both directions. Each crop carries its family, so the chart can work out that dill and carrots are both Apiaceae without anyone asserting it.
- Insectary flowers are a known set of herbs whose flower shape feeds small beneficials.
- Watering conflict follows from whether one plant is a woody Mediterranean herb and the other is not.
- Anything left over is tradition, and says so.
A name that has no guide on this site — nasturtium, leek, fennel and a few others — still appears with its claim, without a link. Leaving it out would misrepresent what the guides say.
Using it to plan a bed
The chart answers "what goes next to this", which is a smaller question than "how do I lay out a bed". Two things matter more than any pairing on it:
Spacing. Crowding does more damage than any bad neighbour. The plant spacing calculator works from the same crop data as this chart, and the square foot garden planner lays a bed out crop by crop.
Grouping by need, not by tradition. The single most useful application of this chart is the watering conflict, because it is the one that actually kills plants. Put the woody herbs — lavender, rosemary, sage, thyme, oregano — together at a dry edge, and keep the thirsty vegetables together where you water. Growing herbs covers that contrast, and planning a vegetable garden layout covers the rest of the bed.
Get the spacing, sun and water right and the neighbours barely matter. That is not a popular thing to say on a companion planting page, but it is what the evidence supports.