RHS hardiness rating
H2 — Tender (frost-free coastal microclimates)
minimum 1-5 °C · minimum 34-41 °F · 250-day growing season
What this rating means
The RHS rating system measures the lowest winter temperature a plant will reliably tolerate. H2 sits at minimum 1-5 °C. In practical UK terms, H2 suits isles of scilly, channel islands, the warmest sheltered pockets of west cornwall and south devon. For comparison with US references, H2 is roughly equivalent to USDA zone 10.
What grows at H2
Plants commonly recommended for H2 UK gardens:
- Echium pininana
- Geranium maderense
- Aeonium (outdoors year-round in Scilly)
- Hedychium (ginger lilies)
- Banana (Musa basjoo with protection — Ensete in milder spots)
- Tree ferns (Dicksonia antarctica) in shelter
- Watsonia
- Salvia leucantha
- Lantana camara
- Agapanthus africanus (the tender evergreen forms)
Climate notes for H2
H2 outdoor gardening works only on the south-west tip of England, the Isles of Scilly, and the Channel Islands. Elsewhere these plants will need a frost-free greenhouse from November through March. Mild winters tempt mainland gardeners to push H2 plants — most lose them in the first hard winter.
Frost dates and growing season
| Typical last spring frost | mid-March (Scilly Isles, Channel Islands) |
|---|---|
| Typical first autumn frost | late November |
| Growing season length | ~250 days |
| Temperature minimum (Celsius) | minimum 1-5 °C |
| Temperature minimum (Fahrenheit) | minimum 34-41 °F |
| Approx USDA equivalent | zone 10 |
Frost dates above are typical for the region the rating describes, not strict cutoffs. A south-facing walled garden in a H2 area can run a fortnight warmer; a frost pocket at the bottom of a valley can run a fortnight colder. Always cross-check against your local Met Office station before sowing tender crops.
When to plant — crop by crop in H2
Sowing, transplant, and harvest dates calibrated to a H2 winter:
- When to plant tomatoes in H2
- When to plant peppers in H2
- When to plant basil in H2
- When to plant garlic in H2
- When to plant lettuce in H2
- When to plant bush beans in H2
- When to plant cucumbers in H2
- When to plant summer squash in H2
- When to plant peas in H2
- When to plant carrots in H2
Source and methodology
Temperature thresholds from the RHS hardiness rating reference. Frost-date typicals are taken from Met Office regional climate summaries for the geographies each rating describes. Plant lists curated by the Growli editorial team from the RHS Find a Plant database and UK extension references. USDA-zone equivalents are approximate cross-references for readers comparing American catalogues.