RHS H5 UK planting calendar
When to plant radishes in RHS H5 (UK)
Sowing, planting, and harvest dates calibrated to H5's 150-day UK season (The Midlands, northern England, inland Wales, lowland Scotland — the band most UK gardens actually sit in once you leave the south coast).
Key dates for radishes at RHS H5
| Stage | When | Anchor |
|---|---|---|
| Direct sow outdoors | late April (24 April) | 21 days before last frost (mid-May) |
| First harvest (estimate) | late May (22 May) | ~28 days from sow |
Dates are typical for the regions H5 describes (The Midlands, northern England, inland Wales, lowland Scotland — the band most UK gardens actually sit in once you leave the south coast). 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 H5
H5 describes UK gardens with winter minima of minimum -15 to -10 °C. Last spring frost typically passes mid-May; first autumn frost arrives mid-October, giving about 150 frost-free days. Radishes prefer the cool damp weather UK springs and autumns deliver — they bolt and turn bitter once daytime temperatures climb above 24 °C, which makes the British shoulder seasons their happiest time.
Radishes are the fastest root crop — spring types mature in 22-30 days from direct sowing, making them ideal row-markers alongside slower crops. Sow 2-4 weeks before the last spring frost as soon as soil can be worked; they bolt and become pithy and peppery hot if left too long in warming soil. Succession-sow every 7-10 days for a continuous harvest; daikon and winter types sown in late summer take 50-70 days and tolerate heavier frost.
UK-specific tips for H5
- H5 covers most of the inhabited UK — Midlands, northern England, lowland Scotland — and radishes need the timing to be more conservative than southern England.
- Cloches and a low polytunnel extend the season at both ends — worth 3-4 weeks of usable growing time in spring and another 2-3 weeks in autumn.
- Cold wet springs are the main pest stress — slugs build up populations in damp soil, and seedlings stall in cool weather. Sow into trays and transplant when soil is reliably above 10 °C, rather than direct-sowing into cold beds.
- Mulch all overwintering plants in November — even hardy perennials lose ground in a freeze-thaw cycle without a 5-7 cm cover of straw or composted bark.
Quick-grow guide
- Sun: Full sun — 6+ hours direct.
- Soil temperature for germination: 7-29 °C (45-85 °F).
- Spacing: 2-3 inches (5-8 cm).
- Days to harvest from direct sow: ~28 days.
- Sow in cool conditions — UK springs and autumns are ideal. Provide some afternoon shade if a heatwave arrives in July.
Common mistakes — H5 × radishes
- Sowing too late: radishes bolt in heat — UK Junes can spike to 28 °C, so the productive window is March-May and again August-October at rating H5.
- Ignoring slug pressure: damp UK springs are slug heaven. Protect rows with copper tape or wool pellets, or sow into modules and transplant when seedlings have toughened up.
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 H5describes. 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 H5 is roughly equivalent to USDA zone 7. Curated by the Growli editorial team.
Keep going
- How to grow radishes — full guide
- RHS H5 — 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 radishes in RHS H3
- When to plant radishes in RHS H4
- When to plant radishes in RHS H6
- When to plant radishes in RHS H7