Silphium perfoliatum

Cup-Plant Asteraceae

A magnificent North American perennial, Silphium perfoliatum, commonly known as Cup Plant, is one of those plants that makes the word ‘architectural’ seem almost inadequate. It forms towering, upright stems clad in enormous opposite leaves, their bases joined around the square stems to create distinctive cup-like structures which collect rainwater — the feature responsible for both its common name and the specific epithet perfoliatum, meaning ‘leaf surrounding the stem’. Above this imposing foliage appear branching sprays of bright yellow, daisy-like flower heads from midsummer into early autumn.

Native from south-eastern Canada through the central and eastern United States, S. perfoliatum is naturally found in moist prairies, open woodland, thickets, stream margins and pond edges. It is therefore rather less interested in the dry prairie conditions tolerated by some of its relatives and is happiest where soil remains reasonably moist. Once established it is a formidable presence, making an excellent backdrop for large-scale naturalistic planting, while the flowers attract butterflies and other pollinating insects and the mature plant provides useful seed for birds. 

In cultivation it is remarkably straightforward provided it is given enough room. Grow in full sun or light shade in fertile, moisture-retentive soil, where it can reach 2.5 m or more. It is particularly effective beside ponds and streams, in damp meadow planting or towards the rear of a large herbaceous border. Staking may be necessary in exposed positions, but otherwise it is admirably undemanding. It can self-seed where conditions suit, so those with smaller gardens may wish to keep an eye on its ambitions — Cup Plant is not a perennial that believes in staying quietly in its allotted corner. 

Height: 150–250 cm
Spread: 50–100 cm
Flowering: July–September
Hardiness: H7, below –20°C
Growing conditions: Fertile, moisture-retentive but well-drained soil; full sun to partial shade. Particularly good in moist soils and alongside ponds or streams.
Range: South-eastern Canada through the central and eastern United States. 
Habitat: Moist prairies, open woodland, thickets, streambanks, pond margins and other damp, open habitats.
Habit: Robust herbaceous perennial with tall, square stems and huge opposite leaves joined around the stem, forming characteristic water-catching cups.
Flowers: Bright yellow, daisy-like heads, approximately 7–9 cm across, carried in branched sprays.
Wildlife: Attractive to butterflies and other pollinating insects; mature plants also provide seed utilised by birds.
Ethnobotany: The species has a history of traditional use among Indigenous peoples of North America, including uses associated with its resinous sap.
Nomenclature: Perfoliatum means ‘having leaves that surround or clasp the stem’, referring directly to the distinctive cup-forming leaf bases.