companion plant

A plant species planted near crop plants to benefit the latter, or two crop plants planted together to benefit one or both. Companion trees are found in forestry (nurse trees) and agroforestry, while in top fruit culture they may aid pollination by belonging to different varieties. A companion may also fix nitrogen, provide physical support for a climbing crop plant, deter pests with their scent etc.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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