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The RHS Award of Garden Merit (AGM) was introduced in the 1920’s by the Royal Horticultural Society and represents the mark of excellence for plants. This exists to help gardeners choose the best all round garden value varieties. The RHS run professional and well executed AGM trials which are a helpful guide for the gardening public.

These trials are undertaken with a limited range of plants, chosen for comparative purposes, and not necessarily conducted on a wide range of site and soil situations. It is a useful guide but far from exhaustive. Trials can take years to find a suitable variety. These plants are mostly selected for their availability from specialist growers. This does not mean that trees that do not have this recognition are less desirable or do not perform as well. The Yellowstone Arboretum has a number of trees and/or shrubs that have trialed successfully according to RHS standards. We have listed them below with location and the year of RHS award.