RHS Award of Garden Merit.
The Award of Garden Merit is a mark of quality awarded, since 1922, to garden plants (including trees, vegetables and decorative plants) by the United Kingdom, Royal Horticultural Society (RHS). Awards are made annually after plant trials intended to judge the plants' performance under UK growing conditions. Trials may last for one or more years, depending on the type of plant being tried out, and may be performed at Royal Horticulture Society Garden in Wisley and other gardens or after observation of plants in specialist collections. Trial reports are made available as booklets and on the website. Awards are reviewed annually in case plants have become unavailable horticulturally, or have been superseded by better cultivars.