Flower · Asteraceae
When to sow cosmos
Thrives on neglect and poor soil. Rich ground gives foliage instead of flowers.
Start seed indoors
4 weeks before
Counted from your last spring frost.
Plant out
1 week after
Counted from your last spring frost.
Sow direct
1 week after
Counted from your last spring frost.
Those weeks become real dates once you name a place.
Timing, in frost-relative terms
Seed packets rarely give calendar dates, because a date that suits one latitude is wrong at another. They give offsets from the last spring frost instead, and those offsets are what make cosmos plantable anywhere.
- Start seed indoors 4 weeks before the last frost.
- Plant out 1 week after the last frost.
- Sow direct 1 week after the last frost.
- Expect 70–90 days to maturity, counted from sowing.
Getting the timing right
Sow direct around the last frost date. Pinch young plants once to produce a bushier, more productive plant.
Frost tolerance
Frost-tender at both ends, but flowers freely until the first autumn frost stops it outright.
Classified as tender, with damage expected below 0°C (32°F)32°F (0°C).