Cup Plant
Silphium perfoliatum — Aster Family
A native perennial wildflower in the Aster Family that blooms in summer and thrives in moist to wet soils.
Planting Guide
When to plant
Plant in spring after the last frost date or in early fall, 6 weeks before the first frost. Container plants establish faster than bare root.
Spacing
Space plants 3.0–4.0 feet apart. Closer spacing fills in faster and suppresses weeds; wider spacing gives each plant room to reach full size.
Root system
Roots reach at least 36 inches deep at maturity. Plant the crown at or just below soil level — the deep root system is why this species handles drought well once established.
Growing Conditions
Sunlight
Part sun to part shade — 3 to 6 hours of direct sunlight. It adapts to a range of exposures and does well on the east or west side of a structure.
Soil & pH
Prefers a wide pH range from acidic to neutral (pH 5.5–7.5). Most average garden soils fall in this range; a quick soil test confirms your starting point.
Watering
High moisture needs. This species thrives in consistently moist soil and is well suited to rain gardens, low spots, pond margins, or areas with supplemental irrigation. Once established (typically 1–2 seasons), it shows moderate drought tolerance and can go extended periods without supplemental water.
Seasonal Care
- Cut back dead stems from last year to 2–3 inches above ground as new growth emerges.
- Top-dress with a thin layer of compost to support the season's growth.
- Deadhead spent flowers regularly to extend bloom period and prevent excessive self-seeding.
- Water deeply during dry spells; mulch around the base to retain moisture.
- No major pruning needed; remove any diseased or damaged foliage promptly.
- Leave stems and seed heads standing through fall and winter to support overwintering insects and birds.
- Divide or transplant in early fall (6 weeks before first frost) for best establishment.
- Leave the plant standing — hollow stems shelter native bees and other beneficial insects overwinter.
- The seed heads attract finches and sparrows through the coldest months.
- No mulching is needed for established plants; a thin layer of leaves is fine around the crown.
Wildlife & Garden Value
Ecological benefits
- Member of the Asteraceae (daisy) family — among the most pollinator-rich plant families. The disk florets provide pollen and nectar to hundreds of bee, butterfly, and hover fly species.
Landscaping uses
- Rain garden plant — thrives in the wet-dry cycles of a bioswale or detention area.
- Pond or stream margin planting for bank stabilization and wildlife habitat.
- Back-of-border accent or screening plant. Tall enough to anchor larger planting beds.
Where to Buy Cup Plant
Buy from specialist native plant nurseries to get the true species rather than a cultivar with reduced wildlife value.
- American Meadows — native seeds and plants
- Prairie Moon Nursery — specialist native plant nursery
- Burpee — seeds with planting instructions