Larkspur · City of Westminster, England, United Kingdom
When to sow larkspurs in City of Westminster
Main outdoor window
17 Mar - 7 Apr
The window this page is built around.
Timed from last spring frost
14 April
In City of Westminster, on your chosen risk.
Ready to pick
15 Jun - 5 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 City of Westminster
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.
Sow direct
17 Mar - 7 Apr
Four weeks before your last frost.
In flower
15 Jun - 5 Jul
Larkspurs through the year
Against the frost risk in City of Westminster
Why these dates
Sow direct four weeks before the last frost, into cool soil - the seed germinates below 15C and often refuses above 18C, which is why late sowings fail. Do not start it indoors; the taproot makes transplanting unreliable. Chilling the seed in a fridge for a fortnight before sowing improves germination markedly.
Hardy to about -12C as a seedling, so autumn sowing works well in zone 7 and milder and produces plants twice the size of spring-sown ones. Collapses in humid heat and will not persist through a subtropical summer.
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. Larkspurs are timed for direct sowing 4 weeks before it, and this page simply resolves those offsets against the frost date computed for City of Westminster.
Hardiness is not the obstacle here. City of Westminster is zone 9a, comfortably inside the range this crop is rated for, so an established plant should come through an average winter without protection.
The median frost-free season here is 219 days, against 90 to 110 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in City of Westminster
Other flowers to time
Growing larkspurs in City of Westminster
When should I plant larkspurs in City of Westminster?
Aim for 17 Mar - 7 Apr in an average year. If you would rather not gamble on the weather, wait until 7-28 Apr - by then frost has finished in nine years out of ten.
When will larkspurs be ready to harvest in City of Westminster?
Expect to start picking around 15 Jun - 5 Jul, based on 90 to 110 days to maturity from the planting date calculated for this location.
How much frost will larkspurs tolerate?
Hardy to about -12C as a seedling, so autumn sowing works well in zone 7 and milder and produces plants twice the size of spring-sown ones. Collapses in humid heat and will not persist through a subtropical summer.