Dutch iris · Zhenjiang, Jiangsu, China
When to sow dutch irises in Zhenjiang
Main outdoor window
14-28 Oct
The window this page is built around.
Timed from last spring frost
19 March
In Zhenjiang, on your chosen risk.
Ready to pick
1 May - 30 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 Zhenjiang
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
14-28 Oct
Four to six weeks before your first frost, so roots form before the ground cools.
In flower
1 May - 30 Jun
Dutch irises through the year
Against the frost risk in Zhenjiang
Why these dates
Plant in autumn, six weeks before the first frost, 10cm deep. In zone 5 and colder, plant in early spring instead, or mulch heavily - these are the least hardy of the common autumn bulbs. Lift and dry the bulbs after the leaves die back if your summers are wet.
Hardy to about -15C, appreciably less than a tulip, and the emerged spring leaves are damaged by a hard late frost even where the bulb survives. Mulch after planting where winters fall below -12C.
Dutch irises 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 Zhenjiang instead of forwards from its start.
Hardiness is not the obstacle here. Zhenjiang is zone 8b, 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 252 days, against 170 to 210 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in Zhenjiang
Other flowers to time
Growing dutch irises in Zhenjiang
When should I plant dutch irises in Zhenjiang?
Aim for 14-28 Oct in an average year. If you would rather not gamble on the weather, wait until 28 Sep - 12 Oct - by then frost has finished in nine years out of ten.
When will dutch irises be ready to harvest in Zhenjiang?
Expect to start picking around 1 May - 30 Jun, based on 170 to 210 days to maturity from the planting date calculated for this location.
How much frost will dutch irises tolerate?
Hardy to about -15C, appreciably less than a tulip, and the emerged spring leaves are damaged by a hard late frost even where the bulb survives. Mulch after planting where winters fall below -12C.