RHS Hardiness Zones
Royal Horticultural Society UK hardiness zones based on average minimum winter temperatures
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H1a
Above 59°F (15°C)
Tropical conditions requiring heated greenhouse year-round
Heated tropical glasshouses
H1b
50°F to 59°F (10°C to 15°C)
Subtropical conditions requiring heated greenhouse in winter
Heated temperate glasshouses
H1c
41°F to 50°F (5°C to 10°C)
Frost-tender plants requiring frost-free conditions
Unheated glasshouses, mild coastal areas
H2
32°F to 41°F (0°C to 5°C)
Tolerates low temperatures but not frost, needs protection
Isles of Scilly, Channel Islands, Coastal Cornwall
H3
23°F to 32°F (-5°C to 0°C)
Hardy in mild areas with some frost tolerance
Coastal South England, South Wales, Coastal Ireland
H4
14°F to 23°F (-10°C to -5°C)
Hardy through most of UK, survives average winters
London, Birmingham, Manchester, Edinburgh
H5
5°F to 14°F (-15°C to -10°C)
Hardy in most areas including severe winters
Yorkshire, Lancashire, Scottish Lowlands
H6
-4°F to 5°F (-20°C to -15°C)
Hardy in all UK regions including exposed uplands
Lake District, Peak District, Scottish Highlands
H7
Below -4°F (-20°C)
Extremely hardy, tolerates severe European winters
Scottish mountains, Northern Scandinavia equivalents