UK hardiness lookup
Aberystwyth (SY23) — RHS hardiness H5
Aberystwyth, Wales · 165-day frost-free season
Frost dates and growing season for SY23
| RHS hardiness rating | H5 |
|---|---|
| Average last spring frost | early May |
| Average first autumn frost | mid-October |
| Growing season length | ~165 days |
| Temperature range (C) | minimum -15 to -10 °C |
| Temperature range (F) | minimum 5-14 °F |
| USDA equivalent | Roughly USDA zone 7a/7b. |
UK frost dates come from Met Office regional climate averages (1991-2020). Frost pockets, valleys, and exposed elevation can shift Aberystwyth-area gardens a full band colder than the regional figure. Coastal and urban gardens run a band warmer.
What grows at RHS H5 in Aberystwyth
Solidly cold-hardy plants. The default working assumption for a "British hardy perennial" away from the south coast.The RHS rates plants — not regions — so check the rating on each plant's tag against this H5 baseline. Anything rated H5 or hardier (numerically higher) should overwinter reliably in a typical Aberystwyth year.
- 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
When to plant in Aberystwyth
Sowing, transplant, and harvest dates for the most common edible crops, calibrated to RHS H5 timing:
- When to plant tomatoes at RHS H5
- When to plant peppers at RHS H5
- When to plant basil at RHS H5
- When to plant garlic at RHS H5
- When to plant lettuce at RHS H5
- When to plant bush beans at RHS H5
- When to plant cucumbers at RHS H5
- When to plant summer squash at RHS H5
- When to plant peas at RHS H5
- When to plant carrots at RHS H5
For a one-shot starting point: tomatoes go outside from the early May window onwards; garlic goes in 4-6 weeks before mid-October; brassicas and salads can run on either side of the frost window with fleece in cold snaps.
Local microclimate notes
Postcode-area ratings are a baseline — your actual garden can sit a band warmer or colder. Urban heat-island effect lifts inner-city gardens; frost pockets at the bottom of slopes drop them. If you can record your own lowest winter temperature for a couple of seasons, that beats any regional average for planning.
For US gardeners reading UK references: RHS H5 is Roughly USDA zone 7a/7b. — see the matching USDA Zone 7 guide for the US-side planting calendar.
Source and methodology
Hardiness rating from the Royal Horticultural Society hardiness rating scale. Frost-date averages from Met Office UK climate averages (1991-2020), matched to the nearest representative regional station for postcode SY23. Plant recommendations curated by the Growli editorial team. Last review 2026-05-19.
Other postcode areas in Wales
- CF1 — Cardiff (RHS H4)
- CF10 — Cardiff (city centre) (RHS H4)
- SA1 — Swansea (RHS H4)
- NP1 — Newport (RHS H4)
- LL30 — Llandudno (RHS H4)
- LL57 — Bangor (Gwynedd) (RHS H5)
- LD — Llandrindod Wells (Powys) (RHS H5)
- Browse all UK postcode areas