RHS hardiness rating
H5 — Hardy (cold UK winter)
minimum -15 to -10 °C · minimum 5-14 °F · 150-day growing season
What this rating means
The RHS rating system measures the lowest winter temperature a plant will reliably tolerate. H5 sits at minimum -15 to -10 °C. In practical UK terms, H5 suits the midlands, northern england, inland wales, lowland scotland — the band most uk gardens actually sit in once you leave the south coast. For comparison with US references, H5 is roughly equivalent to USDA zone 7.
What grows at H5
Plants commonly recommended for H5 UK gardens:
- Geranium (hardy cranesbills)
- Hellebores
- Hosta
- Astilbe
- Iris sibirica
- Phlox paniculata
- Aster (Symphyotrichum)
- Achillea
- Rosmarinus officinalis (most varieties — but mulch crowns)
- Apple, pear, plum, sour cherry, blackcurrant, gooseberry, raspberry, rhubarb
- Vegetables — brassicas, peas, beans, leeks, onions, garlic, potatoes, tomatoes (sheltered)
- Buxus sempervirens, Ilex aquifolium, Taxus baccata
Climate notes for H5
H5 covers the realistic baseline for "is this plant hardy in my garden" across most of the inhabited UK. Use H5 ratings when planning; treat H4 ratings as a risk you have to mulch and protect. Garlic, rhubarb, soft fruit, and most temperate perennials are perfectly happy here.
Frost dates and growing season
| Typical last spring frost | mid-May |
|---|---|
| Typical first autumn frost | mid-October |
| Growing season length | ~150 days |
| Temperature minimum (Celsius) | minimum -15 to -10 °C |
| Temperature minimum (Fahrenheit) | minimum 5-14 °F |
| Approx USDA equivalent | zone 7 |
Frost dates above are typical for the region the rating describes, not strict cutoffs. A south-facing walled garden in a H5 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 H5
Sowing, transplant, and harvest dates calibrated to a H5 winter:
- When to plant tomatoes in H5
- When to plant peppers in H5
- When to plant basil in H5
- When to plant garlic in H5
- When to plant lettuce in H5
- When to plant bush beans in H5
- When to plant cucumbers in H5
- When to plant summer squash in H5
- When to plant peas in H5
- When to plant carrots in H5
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.