Cosmos · Mainz, Rheinland-Pfalz, Germany
When to sow cosmos in Mainz
Main outdoor window
27 Apr - 11 May
The window this page is built around.
Timed from last spring frost
20 April
In Mainz, on your chosen risk.
Ready to pick
6-26 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 Mainz
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
23 Mar - 6 Apr
Four weeks before your last frost, under cover or on a windowsill.
Sow direct
27 Apr - 11 May
One week after your last frost.
Plant out
27 Apr - 11 May
One week after your last frost.
In flower
6-26 Jul
Cosmos through the year
Against the frost risk in Mainz
Why these dates
Sow direct around the last frost date. Pinch young plants once to produce a bushier, more productive plant.
Frost-tender at both ends, but flowers freely until the first autumn frost stops it outright.
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. Cosmos 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 Mainz.
The median frost-free season here is 201 days, against 70 to 90 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in Mainz
Other flowers to time
Growing cosmos in Mainz
When should I plant cosmos in Mainz?
Aim for 27 Apr - 11 May in an average year. If you would rather not gamble on the weather, wait until 11-25 May - by then frost has finished in nine years out of ten.
When will cosmos be ready to harvest in Mainz?
Expect to start picking around 6-26 Jul, based on 70 to 90 days to maturity from the planting date calculated for this location.
How much frost will cosmos tolerate?
Frost-tender at both ends, but flowers freely until the first autumn frost stops it outright.