Possible mechanisms[1] include attracting beneficial insects,[2] repelling pests,[3] or providing nutrients such as by fixing nitrogen,[4] shade, or support.
[5] A large number of companion plant associations have been proposed; only a few of these have been subjected to scientific testing.
Mechanisms that have been scientifically verified include using strongly aromatic plants to deter pests; using companions to hide crops from pests; providing plants as nurseries for beneficial insects including predators and parasitoids; trap cropping;[6] and allelopathy, where a plant inhibits the growth of other species.
The large leaves of these vining plants can help with soil moisture retention.
Strawberries and dewberries create healthy ground cover, clover fixes nitrogen for the blueberries' high needs, yarrow and bay laurel repel unhealthy insects.