A banker plant is a non-crop plant placed among or near the crop to support a breeding population of beneficial organisms. The classic system is cereal plants such as barley or wheat infested with bird cherry-oat aphid (Rhopalosiphum padi), which feeds only on grasses and cannot attack the crop. Parasitic wasps such as Aphidius colemani breed on those aphids and then hunt crop aphids. Flowering plants that provide pollen support predators such as Orius.
In practice
Banker plants make biocontrol self-sustaining rather than relying on repeated purchases. In cannabis they suit greenhouses and long-running mother rooms more than short sealed indoor runs. They need replacing every few weeks as the cereal ages, and they must be scouted like any crop so they do not become a source of pests. Choose host aphids that cannot use cannabis; the rice root aphid, for example, also uses grasses and cannabis roots, so not every grass aphid is safebeing reviewed.
Don't confuse with
- Trap crop: a plant that lures pests away from the crop.
- Companion planting: a broader garden practice with weaker evidence.
