Agrostemma githago aka Corncockle

Agrostemma githago, or corn cockle, is an annual herb. It belongs to the carnation family, Caryophyllaceae. Its native range spans southeast and east Europe to northern Iran. It has spread beyond that range into much of the USA. It grows in fields, meadows, roadsides, and other disturbed ground. Once a weed of grain fields, it has declined with modern farming.

Plants branch as they grow and hold their stems upright. Garden plants reach 2–3 feet [0.6–0.9 metres] tall. RHS gives an upper height of 3.3 feet [1 metre]. They spread about 1–1.6 feet [0.3–0.5 metres] wide. Growth is fast, and the slim green stems bear fine hairs. Narrow, soft leaves grow in pairs along the stems. Each leaf joins the stem without a stalk. Its base clasps the stem, and its edge is smooth. RHS describes grey-green leaves, while NC State lists green ones.

Flowers open through summer on long stalks from the leaf joints. Chicago Botanic Garden lists a wider season, from March through August. Each flower has five pink or purple petals. Dark lines mark the petals near their base. The five sepals reach out beyond the petal edges. Flowers measure about 0.08–0.16 feet [0.025–0.05 metres] across. Most flowers grow alone rather than in dense clusters. Bees visit the flowers, and NC State also records hummingbirds. The fruit forms a capsule with many black, pitted seeds.

Grow corn cockle in full sun and soil that drains well. Sources also list partial shade as a suitable exposure. Sandy soil and loam suit it, including soil low in nutrients. RHS lists acid, neutral, and alkaline soils as suitable. It accepts moist ground and spells of drier soil. Chicago lists moderate watering and USDA zones 4–11. RHS rates its UK hardiness as H5. Weak stems may need stakes to keep them upright. Sow seed where the plants will grow. Removing spent flowers can extend the bloom season. It suits borders, cottage gardens, meadows, and cut-flower beds.

Corn cockle sheds enough seed to spread fast. NC State reports invasive status in West Virginia, Virginia, and Maryland. New Hampshire places it on a watch list. Pests and disease cause few problems, though powdery mildew can occur. All parts can poison people, livestock, and birds. RHS also warns of harm to dogs that eat it. Poisoning may cause gut pain, vomiting, weakness, and slowed breathing. PFAF records cooked leaves as a famine food, with toxicity warnings. It also records past medicinal seed use, not a safe home remedy.