(10/19) The Cup Plant, Silphium perfoliatum, is a member of the Asteraceae family, also known as the sunflower family, and is a great plant for encouraging biodiversity in your garden. It is also a very pretty plant. Its tall, straight stems are very sturdy with no need for staking, even when planted in a windy, unprotected location. My plants grow on top of a hill in
the northwest corner of my garden with no protection from wind. They reach at least six feet tall and their yellow, sunflower-like flowers appear near the top and continue to bloom from July into September with no deadheading.
If you pick a leaf from almost any plant, that leaf will have a little stem-like piece called a petiole. The petiole attaches the leaf to the stem of the plant or the branch of the tree. The cup plant has some leaves with petioles near its base, but most of its leaves do not have petioles.
Why would this fact be important or interesting to note? Because the lack of petioles cause the triangular shaped leaves to wrap around the stem forming a very small cup which then collects moisture from rain and dew. This, of course, is how the plant gets its common name. The tiny amount of water provides moisture for hummingbirds, butterflies, and other insects.
Being a native, the cup plant is not just a pretty face. It is a workhorse that interacts with wildlife in a big way. In addition to the cups that hold needed water for small birds, insects, and sometimes even frogs, the flowers provide pollen and nectar to bees, butterflies, and hummingbirds. In the fall, it's seed heads attract many birds, especially goldfinches.
Cup plants tend to attract red aphids, which seems like a bad thing. The upside is that, in turn, the red aphids attract many beneficial insects like Daddy-long legs, parasitic wasps, Lady bugs, lacewings, robber flies and spiders. You may not like the looks of some of these insects, but they are all carnivorous meaning they eat other insects freeing your garden of
many garden pests.
Cup plants spread vegetatively. They are able to send out long underground stems called rhizomes which have the ability to develop into a new plant. In this way they are able to produce large, dense colonies when growing in optimum conditions. Optimum conditions for this plant is a low lying moist area such as a rain garden. It's long tap root allows it to take up
large quantities of water. Large colonies provide good shelter for birds. They can search in the shade of its large leaves on a hot day while seeking the insects the plants have attracted. Although the plant prefers moist areas, it can survive very well in dry conditions.
If you garden, as I do, in a restricted area where you can't afford to give one plant large areas, but still want to include it in your garden, here is a hint I have found success with over the years.
I buy the black plastic garden edging material that is sold in a roll at any garden supply store. Simply surround the area you are willing to give the plant with the edging. Insert it into the soil as deep as it will go with its rounded top edge just showing above the soil surface. This will restrain the plant very effectively for quite a few years. If a piece does
manage to escape its confinement, it is easy to simply chop it off with a garden spade.
Once a cup plant becomes established, it is difficult to transplant because of its deep tap root. However, the young off-shoots of the plant can easily be dug to be shared with others, transplanted, or eliminated.
Finally, most native plants have a history of edible and/or medicinal qualities attributed to them, and the cup plant is no exception. First, the plant contains amino acids and carbohydrates which makes it a valuable feed plant for farm animals. The resin (sap) was used by the Native Americans to prevent nausea and vomiting. It was also made into a chewing gum to
freshen breath. A powdered form of the plant is used to help alleviate symptoms of fever, dry cough and asthma, and, among other healing qualities, extract from the leaves of the plant has been shown to lower cholesterol and triglycerides levels in blood,
If you are interested in adding this plant to your garden, fall is a good time to plant.