Culture: Easily grown in average, medium to wet soils in full sun. Prefers moist, rich soils, but tolerates some drought once established. Somewhat slow to establish when grown from seed. Self-seeds in optimum growing conditions.
Noteworthy Characteristics: Silphium perfoliatum, commonly called cup plant, is a coarse, sunflower-like, native plant which occurs in low woods and thickets, meadows, prairie stream/pond peripheries and along railroad tracks throughout the State. It typically grows on tough, erect stems to 4-8′ tall and is distinguished from the other silphiums by its square/quadrangular stems and pairs of cup-forming leaves. Flower heads (to 3″ diameter) featuring light yellow rays (20-40) and darker yellow center disks bloom in summer on the upper part of the plant. Rough, triangular to ovate, coarsely-toothed, opposite, connate-perfoliate, medium green leaves. Lower leaves (to 14″ long) are united at the petioles. Middle and upper leaves lack petioles, and leaf pairs are united at the bases to envelop the stem forming a cup (hence the common name). Leaf cups will collect rain water. This species is also commonly called cup rosin weed because its stems (like those of all silphiums) exude a gummy sap when broken or cut.) The genus name Silphium comes from the Greek name silphion, used to refer to a North African resin bearing plant.Specific epithet means with leaves surrounding or embracing the stem, which form the “cup” in this species.
Problems: No serious insect or disease problems.
Garden Uses: A large plant that needs lots of space. Some gardeners find cup plant to be too large and weedy for border rears, but others find it to be an effective backdrop for other perennials. Adapts well to prairies, wildflower/native plant gardens, naturalized areas or moist, open woodland areas including stream/pond edges.
All plant information courtesy of the Missouri Botanical Garden
Standing tall at around six feet (more in wetter soils, less in drier soils), Cup Plant’s yellow blossoms can be seen starting in July when the butterflies visit them, and then later when the birds begin to feed on its seeds. Throughout the growing season, the water held in the leaf cups attract birds and other critters looking for a drink. Cup Plant establishes well in average garden soil or in heavier, wetter soils. It is easy to start from seed by fall planting outdoors, or, if planted in spring, a period of 60 days of moist, cold stratification is recommended prior to sowing.
A vigorous plant throughout its range, this species can be invasive when planted outside of its historic regions. Check the RANGE MAP tab to see if this species is historically native to your state. If your state shows blue-green coloring instead of lime green, this species is best not planted there. It is listed as noxious (pink) in NY and CT. Even within its range, it would not be a good choice for small landscapes as it could overwhelm smaller plants.
As the specific epithet “perfoliatum” suggests, each pair of leaves clasp the stem, making it look like the stem has pierced through them. The leaves themselves form a small basin that allows rain water to collect in tiny pools around the stem, hence the cup comparison. It has been suggested that this may be a primitive form of carnivorous behavior in the plant world. Certainly, one can see how this would set the stage for more specialization in that niche but, at least currently there has been no evidence of the plant gaining any nutritional benefit from the insects that may have drowned in there. It is more likely that this anatomical feature is a way of deterring potential flower predators from crawling up the stem in search of a meal. Indeed, for insects, these pools can form a considerable barrier against vertical movement.
Price range: $6.00 through $12.00
