I have heard them called “yellow daisies” and “yellow sunflowers,” and I agree, the flowers of the Silphium spp. look like both. However, Silphium spp. is actually a yellow aster; the various species of Silphium are members of the asteraceae family.
Silphium spp. is commonly referred to as “rosinweed” due to a pine-scented sap that comes out of the stems of the plant. There are 19 varieties of Silphium found in North America where it grows as a native. Native Americans used the resin from the plant as a type of chewing gum.
The advantage of Silphium spp. is the height they bring to the garden landscape. Typical of many natives, this flower is drought tolerant, likes full sun and will adapt to a variety of soils. The plants flower from June through September.
One of the best things about Silphium is the leaf structure of the plants. The leaves provide contrast, weight and texture and the leaves in the mixed garden.
“Compass plant” or Silphium lacinatum is one of the most common rosinweeds in cultivation. This plant has large leaves – up to 24 inches – at the base of the plant, and they decrease in size as they reach the top of the plant. Compass plant can reach up to nine feet in height, so it’s definitely a “back of the border plant.” The name derives from the way the leaves tend to orient themselves to the north and the south. Songbirds will perch on the stems of the plant, and goldfinches will eat the leaves.
Silphium terebinthiaceum is commonly known as “prairie dock.” This rosinweed has distinct large leaves about 12 inches wide and 24 inches long that grow at the base of the plant. Smooth, leafless stems grow up about eight feet above the leaves of the plant, and the stems bear clusters of yellow flowers that are about three inches wide.
“Slender rosinweed” or Silphium gracile is probably the best variety for the garden. Stems grown four to six feet tall with wide, dark green leaves that start at eight inches at the base of the plant. This variety of Silphium attracts butterflies to its nectar and birds to its seeds.
Three-inch long leaves grace the “wholeleaf rosinweed,” Silphium integrifolium. The plant reaches four to five feet in height, also with yellow flowers. This species is very drought tolerant.
“Cup plant” or Silphium perfolatium has large square stems that come from a pair of leaves that grow together at the base of the plant. Water will collect in the fused leaves, creating a perfect cup for small birds and insects to drink water from. The yellow flowering stems of this plant are anywhere from four to eight feet in height.
Some Silphiums self-seed prolifically, especially in a garden setting where the soil is rich. These plants are well-suited for prairie and native gardens where their self-sowing tendencies are needed. Some suggested North American natives to pair with rosinweed are big bluestem, gray coneflower, rattlesnake master and nodding onion.
Questions or comments related to gardening? Contact Joleen at missourigardener@hotmail.com.
Questions or comments related to gardening? Contact Joleen at missourigardener@hotmail.com