Find a sunny spot for this giant beauty and enjoy the long-blooming riot of yellow flowers in late summer and early fall. Cup plant grows 6-10 feet tall in a wide variety of soil types and medium-to-wet moisture. While it prefers some moisture, it will tolerate occasional drought once established. It usually flowers the second year, and it’s worth the wait. A wide array of butterflies and bees visit this plant for nectar, pollen, and nesting materials. True to its common name, oval-shaped pairs of leaves join at the stem (perfoliatum means "through the leaf," referring to the stem piercing the leaf) to form a cup that catches water and provides a resting place for little critters. Birds will drink from and even bathe in the lofty tubs, and they also shelter in the dense foliage and search for insects. The branched clusters of flower heads are reminiscent of sunflowers, except seeds in sunflowers are produced in the center disk, whereas seeds of the cup plant are produced by the fertile flower rays that surround the center disk. Cup plant is distinguished from others in its genus by its leaves and hairless, square-shaped stem. It has a long tap root and spreads by shallow rhizomes and self-seeding. Even with its deep root system, it tends to topple if planted on slopes or in windy areas.
Native habitats include prairies, floodplains, open woodlands, ditches, and along railroad tracks. It’s stunning on its own or in meadows, gardens, or the backs of borders and beds. When planted 30-40 inches apart, the plants make a dramatic hedgerow or screen.
Reaches 6-10’ tall and 3-4’ wide.
Grows best in full sun, but tolerates part shade.
Prefers well-drained sandy or loamy soil but will grow in rich or poor moist soils, including clay.
Flower heads appear in clusters July-September; 20-30 slender ray flowers surround dark-yellow central disks.
Green, opposite, rough-textured, coarsely toothed leaves are up to 8” long and 5” across, adjoining the smooth, square stem in pairs to form a cup.
Host plant to 6 Lepidoptera species, including specialists giant eucosma (AKA bird dropping moth, pictured here), eucosma bipunctella moth and 2 other specialist moths that rely on Silphium exclusively for their survival, including the Silphium borer pictured here. Long-tongued bees, butterflies, and skippers are the primary pollinators. Short-tongued bees, wasps, and bee flies visit for pollen or nectar. Goldfinches and other birds and small mammals eat the seeds.
Medicinals, Edible, and Other Uses:
Native Americans used the plant for medicinal purposes. The root was used as a tonic and diuretic. The Chippewa used it for lung ailments, hemorrhage, and joint pain.
The young stems and leaves are tasty when sauteed. The nectar produces high-quality honey.
Native American children made chewing gum from the stem’s hardened resin.
Research shows cup plant to be an outstanding forage crop comparable to corn silage, and it has potential as a biofuel. Farmers use it as a pollinator crop due to its long bloom period.
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