RHS H3 UK planting calendar
When to plant potatoes in RHS H3 (UK)
Sowing, planting, and harvest dates calibrated to H3's 230-day UK season (Coastal Cornwall, south Devon, the south coast of England, mild parts of Pembrokeshire and west Wales).
Key dates for potatoes at RHS H3
| Stage | When | Anchor |
|---|---|---|
| Direct sow outdoors | mid-March (19 March) | 21 days before last frost (late March to early April) |
| First harvest (estimate) | mid-June (12 June) | ~85 days from sow |
Dates are typical for the regions H3 describes (Coastal Cornwall, south Devon, the south coast of England, mild parts of Pembrokeshire and west Wales). UK frost pockets, urban heat, and coastal moderation can shift the planting window by 1-2 weeks within the same rating band. Always cross-check against your local Met Office station for current conditions.
Why this timing works at H3
H3 describes UK gardens with winter minima of minimum -5 to 1 °C. Last spring frost typically passes late March to early April; first autumn frost arrives mid-November, giving about 230 frost-free days. Potatoes prefer the cool damp weather UK springs and autumns deliver — they bolt and turn bitter once daytime temperatures climb above 24 °C, which makes the British shoulder seasons their happiest time.
Potatoes are planted as certified seed potatoes (not supermarket tubers) 2-4 weeks before the last spring frost, once soil temperature reaches at least 7 °C; they tolerate light frost in the ground but emerging foliage is killed below -2 °C, so hill soil over any shoots that break through during a late freeze. In zones 9-11 potatoes are a winter or early-spring crop, planted in late January-February to mature before summer heat forces them dormant. Days-to-harvest ranges from 70 days for early/new-potato types to 110-120 days for maincrop storage varieties.
UK-specific tips for H3
- Coastal Cornwall and south Devon gardens can plant potatoes a fortnight earlier than the rest of the UK — late April for tender crops is realistic on a sheltered south wall.
- Wet UK summers drive blight pressure on tomatoes and potatoes — choose blight-resistant cultivars (Crimson Crush, Lizzano, Sarpo Mira) and remove lower foliage to improve airflow.
- Slugs and snails thrive in H3 mildness — overnight checks in May and June are worth the effort.
Quick-grow guide
- Sun: Full sun — 6-8 hours direct.
- Soil temperature for germination: Soil 7-18 °C (45-65 °F) at planting.
- Spacing: 10-15 inches (25-38 cm).
- Days to harvest from direct sow: ~85 days.
- Sow in cool conditions — UK springs and autumns are ideal. Provide some afternoon shade if a heatwave arrives in July.
Common mistakes — H3 × potatoes
- Sowing too late: potatoes bolt in heat — UK Junes can spike to 28 °C, so the productive window is March-May and again August-October at rating H3.
- Ignoring slug pressure: damp UK springs are slug heaven. Protect rows with copper tape or wool pellets, or sow into modules and transplant when seedlings have toughened up.
Source and methodology
RHS hardiness rating thresholds from the official RHS reference. Typical frost-date averages from Met Office regional climate summaries for the geographies H3describes. Crop timing offsets calibrated against UK extension references (RHS sowing calendar, Garden Organic, James Wong's UK growing tables) and cross-checked against US Cooperative Extension Service publications. For American readers cross-referencing, RHS H3 is roughly equivalent to USDA zone 9. Curated by the Growli editorial team.
Keep going
- How to grow potatoes — full guide
- RHS H3 — typical regions and what else to plant
- All RHS hardiness ratings (H1a-H7)
- USDA hardiness zones — for cross-reference with US sources
- Fungus gnats in UK houseplants — guide