unavailability to gardeners, better plants becoming available, affliction by pests or diseases, or insufficient uniformity. Criteria To qualify for an Award of Garden Merit, 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 "Award of Garden Merit" symbol represents a cup-shaped trophy with handles. It is cited together with a hardiness rating as follows: H1 Requires a heated glasshouse H1a Warmer than 15°C/59F: tropical plants for indoors and heated greenhouses H1b 10°C/50F to 15°C/59F: subtropical plants for indoors and heated greenhouses H1c 5°C/41F to 10°C/50F: warm temperate plants that can go outdoors in summer H2 1°C/34F to 5°C/41F: plants that need a frost-free greenhouse in winter H3 −5°C/23F to 1°C/34F: hardy outside in some regions or situations, or which - while usually grown outside in summer - need frost protection in winter (e.g. dahlias) H4 −10°C/14F to −5°C/23F: plants hardy outside in most of the UK in an average winter H5 −15°C/5F to −10°C/14F: plants hardy outside in most of the UK in severe winters H6 −20°C/−4F to −15°C/5F: plants hardy outside in the UK and northern Europe H7 Colder than −20°C/−4F: plants hardy outside in the severest European climates See also List of Award of Garden Merit camellias List of Award of Garden Merit clematis List of Award of Garden Merit dahlias List of Award of Garden Merit dianthus List of Award of Garden Merit flowering cherries List of Award of Garden Merit magnolias List of Award of Garden Merit maples List of Award of Garden Merit narcissus List of Award of Garden Merit rhododendrons List of Award of Garden Merit roses List of Award of Garden Merit sweet peas List of Award of Garden Merit tulips References RHS Plant Finder 2005–2006, Dorling Kindersley (2005) External links The Royal Horticultural Society's website - Search facility for AGM plants RHS AGM Plant Awards RHS Plant Committees Search for AGM plants The Royal Horticultural Society Complete AGM lists Royal Horticultural Society Gardening in the United Kingdom Plant awards