Zone: 3 to 9
Soil: Sand to clay
Light: Full sun to part sun
Bloom colour: Yellow
Bloom period: August to September
Height: 4 to 10 feet
Moisture: Average to moist
Attracts: Bees, butterflies and birds
Notes: All the images shown here are of Silphium perfoliatum, which is the only species that the author has seen in the wild and is the most common member of this genus in Ontario. However, all three species listed below are rare in this province. The cup plant is one of the best native plants to grow. It serves as source of food for a wide range of wildlife and its leaves, which are joined at their bases to form a cup, store water that can be accessed by birds. In my garden, it is one of the more popular plants for Monarch butterflies. It is normally found along riverbanks where its deep roots can access the water table. It will also grow in rain fed gardens in clay or sandy soil.
All three species are large and should be planted at the back of the border where there is some shelter from the wind because heavy storms tend to make the stems flop over or break. The flowers appear as a spray on top of the plant so it would also be a good idea to plant some other quite tall flowers in front of it. All three are noted for their longevity. Cup Plant is the most versatile of the three species tolerating a fair bit of shade. One note of caution; cup plant should only be placed in managed gardens. Every year, a plant produces several daughter plants that are easily pulled. In an unmanaged space, these daughter plants will form a colony. I have seen this plant growing out of control in parks where a single specimen was probably planted.
Silphium perfoliatum - Cup Plant
Silphium laciniatum - Compass plant
Silphium terebinthinaceum - Prairie Dock