Companion planting matrix: exploring four documented pairings

Consult a plant pairing

Access the matrix, located after these instructions. All four fact sheets are initially visible.

1. Select a first plant, then a second from the lists.
2. Press View this pair to display the available fact sheet or the message indicating no fact sheet exists.
3. Read the observation alongside the conditions and limitations and the linked source.
4. Use All fact sheets to return to the complete selection.

After changing your selection, confirm the pairing again to update the result. Reversing the two plants retrieves the same fact sheet; this does not demonstrate a reciprocal benefit. Selecting the same plant twice displays a reminder of its requirements and spacing, without any companion planting note. Without JavaScript, all four fact sheets remain readable, and the filter is inactive.

Distinguishing a trial from a horticultural practice

The Contextualised experimental trial category refers to a measured result within a specific setup. To understand it, consider the species, the environment, the timing of the pairing, and what was actually measured.

The tomato and French marigold fact sheet concerns Tagetes patula and the glasshouse whitefly, Trialeurodes vaporariorum. Trials were conducted in a greenhouse in England: initial planting slowed whitefly development, whereas introduction after heavy infestation had little effect. This result does not guarantee protection outdoors or a yield increase. Trials by Conboy et al.

The lettuce and sweet alyssum fact sheet focuses on romaine lettuces in Salinas, California. The study compares several arrangements and measures dry matter, in particular. This measurement does not correspond to the fresh weight you harvest; nor does it provide an aphid reduction rate applicable to your garden. Study by Brennan

The Documented horticultural practice category describes a way of organising crops proposed by a horticultural organisation. The two RHS fact sheets have practical objectives:

• Small radishes and parsnips: making a slow-emerging row visible, then harvesting the radishes before they interfere with the parsnips. The example concerns small, quick-growing radishes. RHS, sowing radishes
• Lettuce and sweetcorn: temporarily occupying the space between large plants, with lettuces harvested before they are shaded. The success of this arrangement depends on the actual growth of both crops. RHS, space utilisation

These practices do not constitute proof of pest protection. The categories indicate the nature of the available information; they do not rank pairings from best to worst.

Understanding an unlisted pairing

The selection contains only four fact sheets. A search for tomato and parsnip, for example, shows a message saying that no fact sheet has been reviewed here for this pairing. This message describes the content of this tool: it does not claim that these plants are incompatible, that they benefit each other, or that no study exists elsewhere.

The tool therefore assigns neither a score nor a green or red light. It does not fill an absent entry with the conclusion from another pairing. Even when a fact sheet exists, it only addresses the described objective: marking a row, occupying space, or examining a specific result.

Moving from the fact sheet to your project

Before adopting a pairing, formulate the question the fact sheet should answer. “Can I harvest this crop before it is shaded?” allows you to compare your project with the lettuce–sweetcorn fact sheet. “Are these two plants always good neighbours?” goes beyond what it documents.

Keep the source and its limitations with your notes. To subsequently verify space requirements, light, how long the crops occupy the bed, and access to crops, continue with the companion planting guide.