Crown imperial · Ōmuta, Fukuoka, Japan
When to sow crown imperials in Ōmuta
Main outdoor window
2-16 Nov
The window this page is built around.
Timed from last spring frost
10 March
In Ōmuta, on your chosen risk.
Ready to pick
1 Apr - 31 May
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 Ōmuta
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.
Plant the bulbs
2-16 Nov
Four to six weeks before your first frost, so roots form before the ground cools.
In flower
1 Apr - 31 May
Crown imperials through the year
Against the frost risk in Ōmuta
Why these dates
Plant in early autumn, as early as the bulbs can be bought, and deep - 20cm. The bulbs have a hollow crown that collects water and rots, so plant them at a slight tilt or on a handful of grit. They resent disturbance and often skip a year after being moved.
Hardy to about -25C. The smell deters mice and voles, which is a genuine advantage in a garden where tulips get eaten. Needs cold winters and dislikes hot wet summers.
Crown imperials are anchored to the first autumn frost rather than the last spring one, so the planting window on this page counts backwards from the end of the season in Ōmuta instead of forwards from its start.
Ōmuta sits in zone 9b, which is milder than this crop wants, and a winter that never really arrives is its own problem. The dates below still describe the right time of year; the open question is survival rather than timing.
The median frost-free season here is 279 days, against 160 to 200 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in Ōmuta
Other flowers to time
Growing crown imperials in Ōmuta
When should I plant crown imperials in Ōmuta?
Aim for 2-16 Nov in an average year. If you would rather not gamble on the weather, wait until 21 Oct - 4 Nov - by then frost has finished in nine years out of ten.
When will crown imperials be ready to harvest in Ōmuta?
Expect to start picking around 1 Apr - 31 May, based on 160 to 200 days to maturity from the planting date calculated for this location.
How much frost will crown imperials tolerate?
Hardy to about -25C. The smell deters mice and voles, which is a genuine advantage in a garden where tulips get eaten. Needs cold winters and dislikes hot wet summers.