Cup Plant: a beautiful native plant for the landscape
Cup plant, Silphium perfoliatum, is a native plant that can be seen growing in moist ditches in Dodge County as well as in the educational garden outside the Administration Building in Juneau. If you are looking for a native wildflower that will not only bring beauty to your landscape but also provide food and water to a whole host of insects, birds, and amphibians, look no further than this unique specimen.
Cup plant is a member of the Asteraceae family, which not only includes asters but, also some daisies and sunflowers. A sunflower-like perennial, cup plant grows 4–8 feet tall on tough, erect stems requiring no support. They have three-inch flower heads of light-yellow rays surrounding a dark yellow center that bloom on the uppermost portion of the plant from July to September.
Most plants have a petiole: a small stem-like piece that holds the leaf to the main stem. Cup plant, however lacks petioles except on the lowest leaves. Instead, the triangular-shaped, coarse toothed leaves wrap around the stem opposite one another. This forms a small cup where water accumulates, hence the name of the plant. This small accumulation of rain water provides moisture for hummingbirds, bees, butterflies, beetles, and even a few frogs.
Cup plant attracts a host of pollinators. The plant will literally buzz in the summer with bees searching for nectar from the flowers. Bumble bees, cuckoo bees, long-horned bees, leafcutter bees, green sweat bees, and miner bees of several species will all make an appearance.
Bees are not the only pollinators who like the open-faced flowers of the cup plant. A multitude of butterflies, including skippers and swallowtails will frequent it. Several moths use cup plant as their larval host, including silphium moths (Tabenna silphiella) and giant eucosma moths (Eucosma giganteana). Later in the life cycle, finches and sparrows will avail themselves to the seeds of the plant.
Aphid populations on the underside of the leaves are not uncommon. At first glance, this may seem like an unpleasant factor. However, these aphids draw in beneficial insects like parasitic wasps, lady bugs, lacewings, robber flies, and spiders, which will in turn keep detrimental insects at bay in other parts of your landscape.
Cup plant will grow in heavy clay soil and actually helps penetrate the soil to improve it. It will tolerate some sandy soil, although it will do best in moist rich soil. It will tolerate some drought once established. It can be started from seed, but will take several years to flower. Planting from plugs will achieve better results, but still won’t bloom until the second year. Full sun is a must for best performance.
Are there any drawbacks to this work horse, native wonder? Maybe. It is a large, expansive plant and requires significant space to thrive. It might even be a bit of a bully if not managed properly. It can spread vegetatively through rhizomes (underground stems) and colonize under optimum growing conditions. These colonies are wonderful bird havens if you have the space for them. However, if you do not, take steps to contain the plant by surrounding it with an underground barrier like plastic edging. Anything that escapes the barrier can be removed easily.
Carol Shirk
Master Gardener Volunteer