When to plant garlic in RHS H7 (UK)

Key dates for garlic 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. Garlic need a cold period to bulb properly. Plant cloves in autumn so roots establish before the ground freezes; they overwinter dormant and break growth in spring. H7 delivers plenty of chill — perfect for hardneck varieties.

Garlic is the unusual one — plant cloves in autumn (4-6 weeks before the first hard fall frost) so they put down roots before winter, then break dormancy in spring and bulb up over the long days of early summer. Cold-winter zones grow hardneck varieties; mild-winter zones do better with softneck.

UK-specific tips for H7

• H7 territory — high Scottish mountains, Cairngorm fringe, Caithness — gives a 90-day frost-free window. garlic 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: Soil 10-15 °C (50-60 °F) at planting.
• Spacing: 4-6 inches (10-15 cm).
• Days to harvest from autumn planting: ~240 days.
• Mulch with 5-7 cm of straw or shredded leaves once temperatures drop in November.

Common mistakes — H7 × garlic

• Planting too late: H7 winters arrive fast — get cloves in by mid-October so roots establish before the ground freezes. Late November planting risks the cloves rotting in cold wet soil before they root.
• Skipping winter mulch — without a 5-7 cm cover of straw, freeze-thaw cycles can heave cloves out of the soil at H6/H7 elevations.

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 garlic — 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 garlic in RHS H5
• When to plant garlic in RHS H6

Other crops at H7

• When to plant tomatoes in H7
• When to plant basil 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