Zinnia · London, England, United Kingdom
When to sow zinnias in London
Main outdoor window
21 Apr - 5 May
The window this page is built around.
Timed from last spring frost
14 April
In London, on your chosen risk.
Ready to pick
20 Jun - 10 Jul
If you plant at the start of the window.
The average last frost. Half of all years are later than this.
Step by step in London
Each window is a range, not a single day. Earlier in the range buys you a longer season; later in it buys you a safer one.
Start indoors
17-31 Mar
Four weeks before your last frost, under cover or on a windowsill.
Sow direct
21 Apr - 5 May
One week after your last frost.
Plant out
21 Apr - 5 May
One week after your last frost.
In flower
20 Jun - 10 Jul
Zinnias through the year
Against the frost risk in London
Why these dates
Direct sowing after last frost usually beats transplanting - zinnias dislike root disturbance and catch up quickly.
Killed by the first frost at either end of the season. Strictly a warm-season flower.
Seed packets and extension guides express timing as weeks either side of the last spring frost, because that is the only reference point that travels. Zinnias are timed from 4 weeks before that frost for an indoor start, with planting out 1 weeks after it, and this page simply resolves those offsets against the frost date computed for London.
The median frost-free season here is 219 days, against 60 to 80 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in London
Other flowers to time
Growing zinnias in London
When should I plant zinnias in London?
Aim for 21 Apr - 5 May in an average year. If you would rather not gamble on the weather, wait until 12-26 May - by then frost has finished in nine years out of ten.
When will zinnias be ready to harvest in London?
Expect to start picking around 20 Jun - 10 Jul, based on 60 to 80 days to maturity from the planting date calculated for this location.
How much frost will zinnias tolerate?
Killed by the first frost at either end of the season. Strictly a warm-season flower.