Larkspur · Tulsa, Oklahoma, United States
When to sow larkspurs in Tulsa
Main outdoor window
1-22 Mar
The window this page is built around.
Timed from last spring frost
29 March
In Tulsa, on your chosen risk.
Ready to pick
30 May - 19 Jun
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 Tulsa
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
1-22 Mar
Four weeks before your last frost.
In flower
30 May - 19 Jun
Larkspurs through the year
Against the frost risk in Tulsa
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 Tulsa.
Hardiness is not the obstacle here. Tulsa is zone 7b, 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 224 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 Tulsa
Other flowers to time
Growing larkspurs in Tulsa
When should I plant larkspurs in Tulsa?
Aim for 1-22 Mar in an average year. If you would rather not gamble on the weather, wait until 18 Mar - 8 Apr - by then frost has finished in nine years out of ten.
When will larkspurs be ready to harvest in Tulsa?
Expect to start picking around 30 May - 19 Jun, 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.