# Companion Planting Checker

> Check which of your plants go well together, which to keep apart, and why. Checks every pair in a list of up to 40 vegetables, herbs, fruit and flowers for companions and antagonists. Each pair says why — a plain reason such as shared blight or shade, or gardening tradition with weak evidence — and same-family neighbours that share soil pests are listed too.

Part of usefulweb.site (https://usefulweb.site/). Part of [Greenplot](https://greenplot.usefulweb.site/) (ownerApp: greenplot). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://greenplotcompanioncheck.usefulweb.site/ (interactive tool at https://greenplotcompanioncheck.usefulweb.site/tool)
- JSON API: POST https://greenplotcompanioncheck.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://greenplotcompanioncheck.usefulweb.site/api/v1/tool)
- OpenAPI: https://greenplotcompanioncheck.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://greenplotcompanioncheck.usefulweb.site/mcp - tool `greenplot_companion_check`

## Inputs
- plants (multiselect): Plants

## Method
- The pair table is our own compilation: Hearth’s twelve traditional pairs plus about sixty more for Greenplot’s library of vegetables, herbs, fruit and flowers. Every pair is either good (grow together) or bad (keep apart).
- Each pair carries its reason and an evidence label. “Practical” means a plain mechanism: the same disease (late blight on potatoes and tomatoes, verticillium wilt on potatoes and raspberries), shade or competition, a quick crop that is cleared before its neighbour needs the space, pollinators, support for climbers. “Tradition” means gardening lore with weak or no trial evidence; it is shown, never promised.
- Every pair inside your list is looked up once. The score adds 1 per practical good pair and 0.5 per traditional one, and subtracts the same for bad pairs; the verdict is “conflicts” when any practical bad pair is present.
- Same-family neighbours are listed for the families that share soil pests and diseases (potato family, cabbage family, onion family, carrot family, legumes, cucurbits): they are fine together in one season but should move on together in the rotation.

## Limits
- Companion planting is mostly tradition. Spacing, light, water and rotation matter far more than neighbours.