RHS zones

RHS hardiness zonesThe lettering within the RHS zones is as follows:

H – fully hardy

FH – frost hardy

HH – half hardy

FT – frost tender

The RHS system differs somewhat from the USDA and EGF systems since it is based on the growing conditions plants require rather than by dividing the locality into ‘zones’ and identifying plants which can survive in each zone. However, as you can see from the summary diagram, the RHS system can be aligned to the others.

While this system benefits by its simplicity (fewer levels and use of ‘words’ instead of reference numbers) it isn’t able to adapt to changing climates and it is not flexible to expansion. The RHS is now changing its approach to align more closely to more complex, but more accurate and flexible, systems. However, many reference books retain the original RHS categories (usually represented by ’snowflake’ symbols).