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Agrostemma is a genus of flowering plants commonly known as corncockles. They are native to Europe and appear to have originated around the Mediterranean. These plants are very hardy and grow as annuals in almost all regions of the world with minimal need for care. They naturally reseed themselves and can turn invasive. In fact, in some areas, they are specifically classified as noxious weeds and gardeners are discouraged from cultivating them.
The origins of the term “corncockle” are a reference to habit these plants have of growing in or near wheat fields. “Corn” was once a generic term for cereal grains, wheat in particular. Various Agrostemma species were once very common in wheat fields. The development of improved seed filtration technology, combined with changes in how corn is grown, led to a decline in the abundance of these plants.
A. githago, or the common corncockle, is a commonly found species. The common corncockle has upright hairy stems, blade-like leaves, and large pink flowers with black stripes. The flowers have five petals each and little to no odor. Some gardeners grow common corncockle ornamentally, especially in cottage gardens, where plants that tend to sprawl and become slightly leggy can be a popular inclusion. Seeds and seedlings are both available from nurseries and gardeners can also request seeds from friends and neighbors, if they happen to be growing the plant.
Cultivating Agrostemma species is relatively easy. Seeds can be sown in spring directly in the garden or in a greenhouse for transfer after around three weeks. The plants prefer well drained soil and can tolerate both sun and shade, along with a variety of temperatures. They are extremely frost resistant and have low water requirements. The biggest problems gardeners may have are collapse of the long stems, sometimes making it necessary to prop the plants up with stakes, and invasive growth habits. If Agrostemma takes to the conditions where it is being cultivated, it can take over.
Gardeners facing an invasion of unwanted Agrostemma should try to remove the plants before they start going to seed. All visible plants should be dug up and gardeners may want to check the area for seedlings over several weeks. Establishing a fast-growing replacement can help keep seedlings down, although gardeners should avoid replacing one invasive species with another. Another option is to lay out a weed barrier and cover it with fresh soil for growing new plants.