Flower · Asteraceae
When to sow cornflowers
The true blue of the cornfield, and one of very few genuinely blue flowers that will grow from seed scattered on open ground. Cuts and dries well, and the dried petals hold their colour for years.
Start seed indoors
6 weeks before
Counted from your last spring frost.
Plant out
2 weeks before
Counted from your last spring frost.
Sow direct
3 weeks before
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 cornflowers plantable anywhere.
- Start seed indoors 6 weeks before the last frost.
- Plant out 2 weeks before the last frost.
- Sow direct 3 weeks before the last frost.
- Expect 65–85 days to maturity, counted from sowing.
- Hardy in USDA zones 2a–11a.
- Sow again every 21 days for a continuous supply.
Getting the timing right
Sow direct three weeks before the last frost, thinly and where it is to flower - it resents transplanting once the taproot is down. Deadhead relentlessly, because a plant allowed to set seed stops flowering within a fortnight. An autumn sowing gives much taller, sturdier plants.
Frost tolerance
Hardy to about -10C as a young plant, which is what makes autumn sowing possible in zone 7 and milder. Dislikes humid heat and finishes early in a hot summer.
Classified as hardy, with damage expected below -10°C (14°F)14°F (-10°C).