London, United Kingdom · 51.51°
When to plant dahlias in London
The London dates are calculated from the observed last spring frost — a 2016–2025 mean of 6 April — rather than from a latitude estimate or a national calendar. The frost-free season here averages 228 days.
Season anchorobserved 2016–2025
Last spring frost: 6 April · latest 30 Apr
First autumn frost: 20 November · earliest 1 Nov
Frost-free season: 228 days · 10 complete years
These come from the ERA5 reanalysis on a roughly 9 km grid, so they describe the area rather than your plot. A hollow, a frost pocket or an exposed site regularly runs several degrees colder, so use the cautious date for a decision you cannot undo.
Frost date estimator →Local calendar windows
The cautious column is calculated from the latest frost recorded in the period (30 Apr). Use it for tender crops you cannot re-sow.
The year in London
What can move the date
Tubers rot if planted into cold, wet ground, so wait until the frost risk has passed. Stake at planting time, not later — driving a stake in beside a grown plant spears the tuber.
Final spacing: 50 × 70 cm. Soil: pH 6–7.5.
Problems in London
Each has its locally favourable conditions counted month by month, from the weather archive for this city.
Full guide: dahlias diseases and pests →