Plant hardiness defines the lowest temperature at which a plant will survive during the winter.
The zones are defined differently in the UK, the US and Europe.
The UK uses the Royal Horticultural Society (RHS) Zones:
- H – Fully Hardy – Hardy to -15 degrees C (5 degrees F)
- FH – Frost Hardy – Hardy to -5 degrees C (23 degrees F)
- HH – Half Hardy – Hardy to zero degrees C (32 degrees F)
- FT – Frost Tender – Not hardy below 5 degrees C (41 degrees F)
The rest of Europe uses the European Garden Flora (EGF) Zones:
- H1 – Hardy to -20 degrees C (-4 degrees F) and below
- H2 – Hardy to -15 to-20 degrees C (5 to -4 degrees F)
- H3 – Hardy to -10 to -15 degrees C (14 to 5 degrees F)
- H4 – Hardy to -5 to -10 degrees C (23 to 14 degrees F)
- H5 – Hardy to zero to 5 degrees C (32 to 40 degrees F)
- G1 – Requires cool greenhouse protection
- G2 – Requires heated greenhouse protection
The US uses a wider zoning system which is detailed in the diagram below:
