The Award of Garden Merit, or AGM, is an award made to garden plants by the BritishRoyal Horticultural Society after a period of assessment by the appropriate committees of the Society. Awards are made annually after plant trials (which may last for one or more years, depending on the type of plant being trialled) at RHS Garden Wisley and other RHS gardens, or after observation of plants in specialist collections, and are intended to judge the plants' performance for conditions in the UK. Trial reports are made available as booklets and on the RHS website. The awards are reviewed periodically in case plants have become unavailable or have been superseded by more recent, superior cultivars.
To qualify for an AGM, a plant
must be available
must be of outstanding excellence for garden decoration or use
must be of good constitution
must not require highly specialist growing conditions or care
must not be particularly susceptible to any pest or disease
must not be subject to an unreasonable degree of reversion.
The AGM symbol represents a cup-shaped trophy with handles. It should be cited together with a hardiness rating as follows:
H1 Requires heated glass
H2 Requires unheated glass
H3 Hardy outside in some regions or particular situations or which, while usually grown outside in summer, needs frost-free protection in winter (e.g. dahlias)
H4 Hardy throughout the British Isles
H1-2 Intermediate between H1 and H2
H2-3 Intermediate between H2 and H3
H3-4 Intermediate between H3 and H4
H1+3 Requiring heated glass; may be grown outside in summer
For plants requiring heated glass, further guidance is given as follows:
Minimum temperature
15°C Hot glasshouse
10°C Warm glasshouse
2°C Cool glasshouse
Since 1989, France has had similar awards called the Mérites de Courson, but these are drawn from a limited number of plants submitted by nurserymen to juries at the twice-yearly Journées des Plantes de Courson and the prizes are based solely on the opinions of the jury members as to the plants' likely performance in French gardens, not on extensive trials.
References
RHS Plant Finder 2005-2006, Dorling Kindersley (2005) ISBN 1-4053-0736-6
