When to plant basil in RHS H7 (UK)

Key dates for basil at RHS H7

Dates are typical for the regions H7 describes (High Scottish mountains, exposed glens, alpine gardens above 500 m. A tiny fraction of UK gardens experience true H7 conditions.). 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 H7

H7 describes UK gardens with winter minima of minimum below -20 °C. Last spring frost typically passes mid-June; first autumn frost arrives early September, giving about 90 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 H7 that means transplant after the last spring frost (mid-June) and pull plants when autumn cools (early September).

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 H7

• H7 territory — high Scottish mountains, Cairngorm fringe, Caithness — gives a 90-day frost-free window. basil are realistic only with full season-extension kit: polytunnel, fleece, and short-season cultivars.
• Wind chill is the dominant stress — even a healthy plant fails if it sits in a constant 30 mph gale. Walled or netted shelters change what is possible more than any temperature change.
• Soil warmth lags air temperature by 3-4 weeks at H7 elevations — black plastic mulch through April is the difference between a crop and a failure.
• Watch the autumn equinox carefully — once day length drops below 12 hours, most warm-season crops stop ripening regardless of temperature. Pick green and ripen indoors.

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 — H7 × basil

• Choosing a long-season cultivar: H7's 90-day window is too short for big beefsteak tomatoes or long-season peppers — pick short-season cultivars (Glacier, Sub-Arctic Plenty, King of the North).
• Skipping season extension: direct outdoor sowing fails most years at H6/H7 — a polytunnel, cloches, or a fleece-covered raised bed turns a failure into a crop.
• Transplanting into cold soil: even in a polytunnel, UK soil sits below 10 °C until mid-May at this rating. Use black plastic mulch to warm the bed a fortnight ahead of transplanting.

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 H7describes. 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 H7 is roughly equivalent to USDA zone 5. Curated by the Growli editorial team.

Keep going

• How to grow basil — full guide
• RHS H7 — 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 H5
• When to plant basil in RHS H6

Other crops at H7

• When to plant tomatoes in H7
• When to plant garlic in H7
• When to plant lettuce in H7
• When to plant bush beans in H7
• When to plant cucumbers in H7
• When to plant summer squash in H7