Which vegetables grow well together? The best-known companions
The best-known companions are the “Three Sisters” (corn, beans and squash) and French marigold next to tomatoes. For marigold there is a glasshouse trial showing that it slows the growth of whitefly populations on tomato. Many other pairings come from tradition and lack solid evidence.
With documented basis
In the Three Sisters each plant has a job: corn gives support, beans fix some nitrogen, and squash shades the soil and suppresses weeds. For marigolds, a 2019 study in PLoS ONE found that French marigolds grown beside tomatoes all season slowed whitefly development in a glasshouse. Adding them once an infestation was heavy helped little, so plant them alongside the tomatoes from the start.
Tradition to verify
Pairings like carrot and onion or basil and tomato are hugely popular. They do no harm, but don't expect miracles: any effect depends on spacing, timing and climate.
Practical rules
Don't put plants that compete for light and space next to each other. Alternate plant families in your rotation, and leave room for flowers that draw in pollinators and beneficial insects.
In the app
Every plant in the catalogue lists its companions and rotations, so you can plan your beds with some method.
Frequently asked questions
Are online companion charts reliable?
Often not: university extension services warn that many of these lists have no scientific basis.
Does marigold work outdoors?
The study was done in a glasshouse; outdoors the effect may differ.