Agrostemma (Corn Cockle) in Zone 3a & 3b
Agrostemma githago
Yes, agrostemma (corn cockle) grows in zones 3a and 3b. Start seeds indoors May 2–May 9 and plant out May 16–May 23.
When to plant agrostemma (corn cockle) in zone 3b
Zones 3a and 3b share the same average frost dates, so this page covers both.
Method: Either: Start indoors for an earlier harvest, or direct-sow outside for less fuss. Either works.
| Start indoors | May 2–May 9 |
|---|---|
| Direct sow / transplant outside | May 16–May 23 |
| Estimated bloom | Jul 30–Aug 6 (~75 days after planting) |
Spacing: 2 per square foot (square-foot-gardening spacing). Mature height: 2-3 ft.
Plant alongside it in zone 3b
These go outside within two weeks of agrostemma (corn cockle) in zone 3b, so one planting day can cover them.
- AstilbeMay 16–May 23
- Bachelor's Button (Cornflower)May 16–May 23
- Basket-of-GoldMay 16–May 23
- Bupleurum (Thoroughwax)May 16–May 23
- CalendulaMay 16–May 23
- California PoppyMay 16–May 23
Agrostemma, better known as corn cockle, has a history as an unwanted weed in European grain fields before it found a second life as a deliberately grown cut flower. Its delicate, magenta-pink blooms on tall, wiry stems have the airy, cottage-garden look that's hard to get from a sturdier, more structured flower.
How agrostemma (corn cockle) fits zone 3's season
Zone 3b's frost-free window runs about 98 days, from May 30 to September 5. Agrostemma (corn cockle) needs about 75 days from sowing to first bloom.
Agrostemma (Corn Cockle) planting windows in every zone
Zone 3b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 2a & 2b | Apr 22–Apr 29 | May 6–May 13 | Jul 20–Jul 27 |
| 3a & 3b (your zone) | May 2–May 9 | May 16–May 23 | Jul 30–Aug 6 |
| 4a & 4b | Apr 17–Apr 24 | May 1–May 8 | Jul 15–Jul 22 |
| 5a & 5b | Apr 12–Apr 19 | Apr 26–May 3 | Jul 10–Jul 17 |
| 6a & 6b | Mar 28–Apr 4 | Apr 11–Apr 18 | Jun 25–Jul 2 |
| 7a & 7b | Mar 13–Mar 20 | Mar 27–Apr 3 | Jun 10–Jun 17 |
| 8a & 8b | Feb 25–Mar 4 | Mar 11–Mar 18 | May 25–Jun 1 |
| 9a & 9b | Jan 18–Jan 25 | Feb 1–Feb 8 | Apr 17–Apr 24 |
| 10a & 10b | Jan 2–Jan 9 | Jan 16–Jan 23 | Apr 1–Apr 8 |
| 11a & 11b | Dec 4–Dec 11 | Dec 18–Dec 25 | Mar 3–Mar 10 |
Bloom dates are about 75 days after the sow or plant-out date, not after starting seeds indoors.
Zone 2 sows before zone 3 here, which looks wrong and is not. USDA zones rank winter cold, not season length, and zone 2 is mostly interior Alaska, where hard winters come with warm summers. More on what a zone measures.
Good companions
No well-established companions for agrostemma (corn cockle).
Where to buy agrostemma seeds
None of the seed suppliers we list carries agrostemma seeds right now. A local garden center or a specialty seed house is the place to look.
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing agrostemma (corn cockle)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 3b calendar · Plan your beds in the Garden Designer →
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Growing Agrostemma (Corn Cockle) in USDA zone 3b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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