When to plant basil in RHS H2 (UK)

Key dates for basil at RHS H2

Dates are typical for the regions H2 describes (Isles of Scilly, Channel Islands, the warmest sheltered pockets of west Cornwall and south Devon). 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 H2

H2 describes UK gardens with winter minima of minimum 1-5 °C. Last spring frost typically passes mid-March (Scilly Isles, Channel Islands); first autumn frost arrives late November, giving about 250 frost-free days. Basil are tender — they need soil above 10 °C to grow and stop setting fruit when night temperatures drop below 10 °C. At H2 that means transplant after the last spring frost (mid-March (Scilly Isles, Channel Islands)) and pull plants when autumn cools (late November).

Basil is one of the most cold-sensitive common herbs — it sulks below 10 °C and dies in light frost. Wait a full week after the last spring frost before moving transplants outside, or direct-sow two weeks after frost when soil hits 18 °C.

UK-specific tips for H2

• Basil grow well outdoors in the Scilly Isles and Channel Islands but are still vulnerable to occasional spring frosts — keep horticultural fleece to hand through April.
• Slug pressure is severe in mild damp winters — start beer traps and copper rings in March, not when you see damage.
• Wind exposure trumps temperature in H2 coastal pockets. Salt-laden gales burn foliage as quickly as any frost — establish a windbreak before you plant.

Quick-grow guide

• Sun: Full sun — 6+ hours direct.
• Soil temperature for germination: 20-25 °C (68-77 °F).
• Spacing: 8-12 inches (20-30 cm).
• Days to harvest from transplant: ~60 days.
• Wait until soil reaches 10-12 °C before transplanting outdoors — cold UK soils stall tender crops for weeks.

Common mistakes — H2 × basil

• Treating UK climate like the US zone 10: 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 H2describes. 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 H2 is roughly equivalent to USDA zone 10. Curated by the Growli editorial team.

Keep going

• How to grow basil — full guide
• RHS H2 — 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

Same crop, nearby ratings

• When to plant basil in RHS H1b
• When to plant basil in RHS H1c
• When to plant basil in RHS H3
• When to plant basil in RHS H4

Other crops at H2

• When to plant tomatoes in H2
• When to plant peppers in H2
• When to plant garlic in H2
• When to plant lettuce in H2
• When to plant bush beans in H2
• When to plant cucumbers in H2