Poppies are ornamental plants desired for their colorful flowers. Poppy varieties grow in U.S. Department of Agriculture hardiness zones 2 to 9. Cultivars offer many flower and foliage combinations. These flowering plants, available as annuals and perennials, grow as ground-hugging 4-inch flowers or 4-foot upright clumps. Poppy flowers last for a few days and then fade. Under favorable conditions, they spread in the home garden but are rarely invasive.
Poppies typically spread through seed formation. The flowers die back and yield seed pods that mature in summer. The seed pods dry and shed seeds around the plant. Most poppy seeds are so tiny that they blow easily in the wind. Birds also eat the seeds and spread them. Many poppies, like California poppies, take root easily. They quickly spread across a hillside and may yield several generations in a season. Poppies self-sow in late summer or autumn and germinate the following spring.
Some poppies spread through roots that produce adjacent plants. Perennials such as the Oriental poppy can be left in place for years. They gradually spread into plant clumps that can be divided into new plants. These poppies spread both through seeds and roots. These poppies die back in late summer and foliage often disappears, only to emerge in spring from the root base. Leave room around clumping poppies. They are not aggressive in crowding out other plants, but do need room to spread. If they are too large for the garden spot, divide the clumps or sever the roots to slow plant growth.
A few poppies, such as the California native Matilija poppy, spread aggressively through their roots. Matilija poppies grow through tenacious rhizomes or underground roots. Called the fried egg poppy for its yellow-centered white flower, this poppy grows into a shrub 4 feet or taller. It is a tough desert wildflower that survives drought and poor soil. It spreads into the surrounding area through its root network that puts up root suckers as new plants. It is hard to propagate, but once it is established this type of poppy takes over a garden corner.
Gather poppy seeds when the pods turn brown. Most poppy pods resemble small globes or urns. The seeds mature inside. Remove them by shaking the pod upside down so the seeds fall from the holes. Or crush the dry pod and sift out the tiny round seeds. The California poppy matures into a slender pod 1 to 2 inches long. Snip off these pods before they are fully ripe. Drop them in a paper bag or covered container. When each pod is dry and brittle, it spontaneously pops open and scatters seeds several feet. The slightest touch to a dry pod will snap it open and throw seeds to the ground.