RHS H4 UK planting calendar
When to plant dill in RHS H4 (UK)
Sowing, planting, and harvest dates calibrated to H4's 180-day UK season (Most of southern England, the south Midlands, south Wales, and coastal areas across the rest of the UK).
Key dates for dill at RHS H4
| Stage | When | Anchor |
|---|---|---|
| Direct sow outdoors | early April (4 April) | 21 days before last frost (late April) |
| First harvest (estimate) | early June (3 June) | ~60 days from sow |
Dates are typical for the regions H4 describes (Most of southern England, the south Midlands, south Wales, and coastal areas across the rest of the UK). 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 H4
H4 describes UK gardens with winter minima of minimum -10 to -5 °C. Last spring frost typically passes late April; first autumn frost arrives late October, giving about 180 frost-free days. Dill 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.
Dill develops a taproot early and transplants very poorly, so always direct-sow into its permanent spot 2-4 weeks before the last spring frost once the soil reaches at least 10 °C. It is hardy to light frosts and germinates in as little as 7 days in warm soil. Like cilantro, dill bolts quickly when temperatures climb above 27 °C (80 °F); successive small sowings every 2-3 weeks extend the leafy harvest, and a late sowing allowed to go to seed provides dill seed for pickling.
UK-specific tips for H4
- H4 is the typical southern English garden — dill grown outdoors here perform similarly to USDA zone 8b/9a Americans seeing in their references.
- Wet July-August stretches drive blight and powdery mildew — water early in the day, mulch to reduce splash, and remove lower foliage as plants establish.
- Slug pressure peaks in May after the first warm wet spell — protect young transplants for the first three weeks with copper tape or wool pellets.
- Light intensity is lower than in equivalent USDA zones — UK summer days are long, but cloud cover means more total hours but lower instantaneous photon flux than a US zone 8 garden. Plants tend to be leafier and slower to ripen.
Quick-grow guide
- Sun: Full sun — 6-8 hours direct.
- Soil temperature for germination: 10-27 °C (50-80 °F).
- Spacing: 9-12 inches (23-30 cm).
- Days to harvest from direct sow: ~60 days.
- Sow in cool conditions — UK springs and autumns are ideal. Provide some afternoon shade if a heatwave arrives in July.
Common mistakes — H4 × dill
- Sowing too late: dill bolt in heat — UK Junes can spike to 28 °C, so the productive window is March-May and again August-October at rating H4.
- 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 H4describes. 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 H4 is roughly equivalent to USDA zone 8. Curated by the Growli editorial team.
Keep going
- How to grow dill — full guide
- RHS H4 — 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 dill in RHS H2
- When to plant dill in RHS H3
- When to plant dill in RHS H5
- When to plant dill in RHS H6