Award of Garden Merit

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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 a mark of quality awarded to garden plants by the British 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 trialled, and may be performed at RHS Garden, Wisley, other RHS gardens or after observation of plants in specialist collections. Trial reports are made available as booklets and on the RHS website. Awards are reviewed periodically in case plants have become unavailable horticulturally, or have been superseded by more recent, superior cultivars.

The AGM should not be confused with the RHS Award of Merit (AM), given to plants deemed 'of great merit for exhibition' i.e. for show, not garden, plants.

To qualify for an AGM, a plant

  • must be available horticulturally
  • 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 is cited together with a hardiness rating as follows:

  • H1 Requires a heated glasshouse (hot glasshouse, minimum temperature 15°C; warm, minimum 10°C; cool, minimum 2°C)
  • H2 Requires an unheated glasshouse
  • H3 Hardy outside in some regions or situations, or which - while usually grown outside in summer - needs frost 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 a heated glasshouse as above, but may be grown outside in summer

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 awards are based solely on the opinions of the jury members as to the plants' likely performance in French gardens, rather than on extensive trials.

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