Open dataset · CC-BY 4.0
RHS Hardiness Ratings — H1a to H7 scale with °C bands
| RHS rating | Minimum temperature tolerated | What it means for UK growing |
|---|---|---|
| H1a | above about 15 °C (warm, never cold) | Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever. |
| H1b | about 10 °C (sustained cold below this is damaging) | Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. |
| H1c | about 5 °C (and never frost) | Warm-temperate — can summer outdoors but must come in well before the first frost. |
| H2 | about 1 to 5 °C — tolerates cold but no real frost | Tender — survives a frost-free greenhouse or a very mild, sheltered spot. |
| H3 | about −5 to 1 °C — a light, short frost only | Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. |
| H4 | about −10 to −5 °C | Hardy in an average winter across much of the temperate world. |
| H5 | about −15 to −10 °C | Hardy in most of the UK and in cold winters. |
| H6 | about −20 to −15 °C | Hardy throughout the UK and northern Europe. |
| H7 | below about −20 °C | Hardy in the severest European continental winters. |
Methodology
Ratings and temperature bands reproduce the published RHS plant-hardiness rating scale, verified May 2026 against the official RHS hardiness-rating document. The "what it means" column is a plain-language gloss of each band for UK growers; it adds no temperatures the RHS scale does not define.
Sources
- Royal Horticultural Society — plant hardiness ratings (rhs.org.uk)
Last verified 2026-05-15.
License & citation
This dataset is published under Creative Commons Attribution 4.0. You may reuse it commercially or non-commercially with credit. Suggested attribution:
RHS hardiness-rating reference table compiled by Growli (getgrowli.app), CC-BY 4.0, from the Royal Horticultural Society plant-hardiness rating scale.
Want this applied to your actual garden?
A table tells you the rule. The Growli app tells you what to do — it knows your plants, your zone, and your local weather, and turns reference data like this into daily watering, frost, and repot reminders.