RHS H6 UK planting calendar
When to plant garlic in RHS H6 (UK)
Sowing, planting, and harvest dates calibrated to H6's 120-day UK season (Upland Scotland, the Cairngorms foothills, the Pennines, high ground in the north of England and north Wales).
Key dates for garlic at RHS H6
| Stage | When | Anchor |
|---|---|---|
| Plant cloves outdoors | late August — early September (about 35 days before the first autumn frost) | 35 days before first autumn frost (early October) |
| First harvest (estimate) | early May of the following year | ~240 days from autumn planting |
Dates are typical for the regions H6 describes (Upland Scotland, the Cairngorms foothills, the Pennines, high ground in the north of England and north 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 H6
H6 describes UK gardens with winter minima of minimum -20 to -15 °C. Last spring frost typically passes late May to early June; first autumn frost arrives early October, giving about 120 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. H6 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 H6
- H6 gardens — Highland Scotland, Pennine uplands — have a short growing season, and garlic need either a polytunnel or a south-facing wall to deliver a reliable crop.
- Wind exposure cuts as much as 2 °C off ambient temperature in upland gardens — site beds in the lee of a hedge or wall before worrying about frost dates.
- Choose short-season cultivars: tomatoes (Glacier, Sub-Arctic Plenty), peppers (King of the North), squash (Spirit, Sweet Mama). Long-season heirlooms will run out of summer before they finish.
- Cool wet ground keeps soil temperatures below 10 °C well into May — black plastic mulch or biodegradable paper mulch lifts soil temperature by 3-4 °C and brings sowing dates forward by two weeks.
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 — H6 × garlic
- Planting too late: H6 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 H6describes. 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 H6 is roughly equivalent to USDA zone 6. Curated by the Growli editorial team.
Keep going
- How to grow garlic — full guide
- RHS H6 — 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