RHS hardiness rating
H7 — Very hardy (extreme winter cold)
minimum below -20 °C · minimum below -4 °F · 90-day growing season
What this rating means
The RHS rating system measures the lowest winter temperature a plant will reliably tolerate. H7 sits at minimum below -20 °C. In practical UK terms, H7 suits high scottish mountains, exposed glens, alpine gardens above 500 m. a tiny fraction of uk gardens experience true h7 conditions.. For comparison with US references, H7 is roughly equivalent to USDA zone 5.
What grows at H7
Plants commonly recommended for H7 UK gardens:
- Native pines and spruces
- Larix (larch)
- Sorbus, alder, birch
- Salix lapponum and dwarf willows
- Alpine campanulas and saxifrages
- Empetrum nigrum (crowberry)
- Vaccinium myrtillus, V. vitis-idaea (lingonberry)
- Dryas octopetala
- Primula auricula
- Hardy ferns — Dryopteris filix-mas, Polystichum
- Cold-tolerant vegetables only — kale, cabbage, broad beans, peas, early potatoes
Climate notes for H7
H7 territory is genuinely tough gardening. Build for wind first, cold second — wind chill and exposure kill more plants than absolute temperature. Use a polytunnel for anything beyond brassicas, peas, and broad beans. Almost everything ornamental should come from alpine or boreal stock.
Frost dates and growing season
| Typical last spring frost | mid-June |
|---|---|
| Typical first autumn frost | early September |
| Growing season length | ~90 days |
| Temperature minimum (Celsius) | minimum below -20 °C |
| Temperature minimum (Fahrenheit) | minimum below -4 °F |
| Approx USDA equivalent | zone 5 |
Frost dates above are typical for the region the rating describes, not strict cutoffs. A south-facing walled garden in a H7 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 H7
Sowing, transplant, and harvest dates calibrated to a H7 winter:
- When to plant tomatoes in H7
- When to plant basil in H7
- When to plant garlic in H7
- When to plant lettuce in H7
- When to plant bush beans in H7
- When to plant cucumbers in H7
- When to plant summer squash in H7
- When to plant peas in H7
- When to plant carrots in H7
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.