Companion planting charts encode real relationships.
Most companion-planting advice you'll find online is folklore, and the charts have no scientific basis. A few pairings do have real mechanisms. Here's what we can actually defend, and why.
What is actually known
Companion-planting charts are not a record of tested relationships. The idea is old. Plants were once matched by the four elements and the signs of the zodiac, and later by pseudoscientific methods such as sensitive crystallization of plant extracts, and there is no scientific basis for any of the lists. A minority of pairings do have real, named mechanisms: mixed plantings confuse pests hunting for their host plant by sight and smell, a squash canopy works as a living mulch, and diverse plantings keep beneficial predators and parasitoids around. Those are recorded here as a good hunch. Most chart entries have nothing behind them.
The evidence
Evidence: checked against 1 source in the research-based literature.
The source
There is no scientific basis, however, for any of the several lists that exist describing
What we can actually defend
- Aromatic species interplanted with brassicas are reported to reduce cabbage-worm damage. The mechanism is unresolved and trial results are mixed.
- Alliums interplanted with carrots reduce carrot rust fly damage.
- Insectary plants near fruiting crops increase pollinator and predator visitation.
- Living mulch suppresses weeds and conserves soil moisture.
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Cite this page
Milpa Gardens. “Companion planting charts encode real relationships.” Evidence grade: Refuted. https://milpa.garden/beliefs/companion-planting-companion-chart/
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.