Growing Agrostemma (Corn Cockle): A Complete Profile
By Growing Home Greens Team · August 10, 2026
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.
Sowing it for cool weather
Direct-seeding is the recommended method, sown 1/8 inch deep as soon as the soil is workable, or start indoors 4 to 5 weeks before your last frost. Germination takes 7 to 14 days at 60-70°F. Thin plants to 6 to 9 inches apart once the first true leaves appear; mature plants reach 24 to 36 inches tall.
Agrostemma performs best in cool conditions, blooming in July and August from an early spring sowing. For continuous bloom rather than one early flush, sow a new round every 2 to 3 weeks through midsummer.
Harvest early in the spray
Cut for a vase when just 1 to 2 flowers in a spray have opened; the rest continue opening after cutting, which extends the useful bloom window well past the initial harvest.
Agrostemma has no well-established companion pairings, and nothing it needs to be kept away from. At 2 plants per square foot, it works well in a dedicated cutting row in the Garden Designer, timed for the cool part of the season.
Source: Agrostemma (Corn-Cockle): Key Growing Information, Johnny’s Selected Seeds.
Companion planting guide for Agrostemma (Corn Cockle) · Find your planting dates
Typically viable in USDA zones 2-11. Not sure your zone? Look it up by ZIP code.
Mature height: 2-3 ft
Method: Either: Start indoors for an earlier harvest, or direct-sow outside for less fuss. Either works.
When to plant agrostemma (corn cockle), by zone
Every zone agrostemma (corn cockle) grows in. Pick your zone in the header and it will be highlighted here. Each zone links to its full page.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 2a & 2b | Apr 22–Apr 29 | May 6–May 13 | Jul 20–Jul 27 |
| 3a & 3b | 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.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Agrostemma (Corn Cockle) plants fit per square foot?
Spacing: 2 per square foot (square-foot-gardening spacing). Mature height: 2-3 ft.
Varieties worth considering
- Straight-species agrostemma (Agrostemma githago): Johnny's Selected Seeds sells this species in a couple of named color strains (the classic magenta-pink and a paler 'Ocean Pearl' white); the growing requirements are consistent across them, so the species itself covers what matters for care. (source)
- 'Purple Queen' agrostemma (best for: classic magenta cut flower): Johnny's Selected Seeds describes this as an elegant cut flower for early-season production, the classic deep-magenta corn cockle color. (source)
- 'Blossom Pearl' agrostemma (best for: blush pink color): Johnny's Selected Seeds lists this as producing blush pink blooms on long graceful stems, a softer color option than the standard magenta or white forms. (source)
Why each variety is listed comes from the source shown next to it. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement. The buy links are separate from those sources: they go to seed suppliers that sell that exact variety, and we may earn a commission on some of them.
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.
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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)
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Growing Agrostemma (Corn Cockle): A cottage-garden annual with delicate, magenta-pink blooms on wiry stems, an old European grain-field weed now grown deliberately as a cut flower.
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