Gentle giants have their place in gardens, and the cup plant is a perfect example. This tallgrass prairie perennial looms like a small tree over lesser flowers, but a crown of bright yellow daisylike blooms—which appear in late summer, just when the rest of the garden is crying uncle, and last until fall—makes it easy to forgive its excesses. Wildlife find this plant irresistible: it offers flowers for butterflies, seeds for birds, and a cool drink for all when dew or rain falls in the cups formed by leaves that encircle the stem.
Common name: Cup plant, rosinweed, cup rosinweed
Botanical name: Silphium perfoliatum
Plant type: Perennial
Zones: 3 to 9
Height: 4 to 8 feet
• Sun: Full sun
• Soil: Average
• Moisture: Medium to wet
• Mulch: Mulch to preserve moisture in the soil.
• Pruning: None needed.
• Fertilizer: None needed.
• By seed or by division
Pests and diseases
• Vulnerable to leaf spot, downy mildew, and rust.
• Not typically a target of pests.
• S. perfoliatum attracts birds and butterflies. Birds and insects drink dew or rain from the “cup” formed by the perfoliate leaves. In the fall, goldfinches eat the seeds.
• Cup plant may need staking unless it’s grown near other tall plants. Because it’s such a large plant, it’s best in prairie gardens or at the back of a big perennial border. Or use it as a screen or for colonizing a large area.
• The plant has a long taproot that’s difficult to dig out, so think carefully about where you plant it.
• S. perfoliatum can be aggressive. It will self-seed under the right conditions. It’s not a problem plant in most areas, but it is considered invasive in some parts of the Northeast.
All in the family
• There are about 20 species in the genus Silphium, all found in Canada and the United States. Cup plant, compass plant (S. laciniatum), and prairie dock (S. terebinthinaceum) are the most widely available.
Where to buy
• Ion Exchange, Harpers Ferry, IA, 800-291-2143, www.ionxchange.com
• Romence Gardens, Grand Rapids, MI, 888-907-5268, www.romencegardens.com
(Photo of Silphium perfoliatum courtesy of Missouri Botanical Garden’s Kemper Center for Home Gardening)