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Trials field at Wisley showing some of the hundreds of varieties assessed for the Award of Garden Merit
The Award of Garden Merit, or AGM, is an award made to garden plants by the Britishmarker Royal 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, Wisleymarker 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 The awards are reviewed periodically in case plants have become unavailable or have been superseded by more recent, superior cultivars.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 Coursonmarker, 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.


  • RHS Plant Finder 2005-2006, Dorling Kindersley (2005) ISBN 1-4053-0736-6

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