RHS H3 UK planting calendar
When to plant eggplant 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 eggplant at RHS H3
| Stage | When | Anchor |
|---|---|---|
| Indoor seed start | early February (5 February) | 9 weeks before last frost |
| Outdoor transplant | late April (23 April) | 14 days after last frost (late March to early April) |
| First harvest (estimate) | mid-July (12 July) | ~80 days from transplant |
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. Eggplant are tender — they need soil above 10 °C to grow and stop setting fruit when night temperatures drop below 10 °C. At H3 that means transplant after the last spring frost (late March to early April) and pull plants when autumn cools (mid-November).
Eggplant needs more heat than tomatoes or peppers — transplant only after soil reaches 18 °C (65 °F) and night temperatures stay consistently above 13 °C (55 °F); cold soil causes prolonged transplant shock and purple-leaf discolouration. Start seeds 8-10 weeks before last frost at a soil temperature of 27-30 °C for good germination rates. In zones 3-5, rely on long-season indoor starts and black plastic mulch to boost soil heat.
UK-specific tips for H3
- Coastal Cornwall and south Devon gardens can plant eggplant 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: 24-30 °C (75-85 °F).
- Spacing: 18-24 inches (45-60 cm).
- Days to harvest from transplant: ~80 days.
- Wait until soil reaches 10-12 °C before transplanting outdoors — cold UK soils stall tender crops for weeks.
Common mistakes — H3 × eggplant
- Treating UK climate like the US zone 9: although temperature minima match, UK summers are cooler, wetter, and cloudier. Add 1-2 weeks to days-to-harvest figures from US sources.
- Sowing into cold wet soil: UK spring soil holds water longer than equivalent US zones. Wait for soil to dry enough to crumble in your hand before sowing.
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 eggplant — 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