RHS H6 UK planting calendar
When to plant rhubarb 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 rhubarb at RHS H6
| Stage | When | Anchor |
|---|---|---|
| Direct sow outdoors | mid-May (19 May) | 21 days before last frost (late May to early June) |
| First harvest (estimate) | mid-November (17 November) | ~547 days from sow |
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.
Rhubarb is planted as divisions or crowns in early spring while the soil is still cool, 2-3 weeks before the last frost; it is extremely cold-hardy and actually requires winter chilling to break dormancy (reliably hardy to zone 3, marginal in zones 9-10 where inadequate chilling reduces vigour). Do not harvest in year one; take only 2-3 stalks per plant in year two; harvest freely from year three onward, always leaving at least 3-4 strong stalks per crown. Never eat the leaves — rhubarb foliage contains toxic oxalates at harmful concentrations.
UK-specific tips for H6
- H6 gardens — Highland Scotland, Pennine uplands — have a short growing season, and rhubarb 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 (tolerates light afternoon shade in hot zones).
- Soil temperature for germination: Soil 4-10 °C (40-50 °F) at crown planting.
- Spacing: 36-48 inches (90-120 cm).
- Days to harvest from direct sow: ~547 days.
- Wait until soil reaches 10-12 °C before transplanting outdoors — cold UK soils stall tender crops for weeks.
Common mistakes — H6 × rhubarb
- Treating UK climate like the US zone 6: 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 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 rhubarb — 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