Silphium perfoliatum - Cup plant

Silphium perfoliatum, the cup plant, is a giant perennial with sturdy stems that bear numerous bright yellow daisy-like flowers in high summer. Its ample foliage has a remarkable feature: the leaves join around the stems, forming small cups capable of holding rainwater. This very hardy, long-lived plant is visited by pollinating insects and is at home in a naturalistic meadow, on a bank, or in a spot in the garden where its roots can spread at will.

The cup plant belongs to the Asteraceae family, like sunflowers, rudbeckias and asters. It is a herbaceous deciduous perennial: its stems die back in autumn, and new shoots emerge from the rhizome in spring. This wild plant is native to south-eastern Canada and much of the central and eastern United States. It grows in damp meadows, meadows near rivers, ditches, damp woodland edges and around lakes. Its rhizome develops deep roots as well as superficial rhizomes that spread gradually. A mature plant reaches 2 to 2.50m in height with a spread of 80cm to 1m, but several plants can eventually form a much larger colony. The thick, upright stems have four well-marked angles. They are sparingly branched in their lower part, then divide at the top to bear the flowers. The medium green leaves are arranged in pairs. Oval to broadly lanceolate, coarsely toothed and rough to the touch, they measure 15 to 25cm in length. The base of each pair of leaves surrounds the stem: the leaf appears to be pierced by it, which explains the name perfoliatum. The small cavity they form collects dew and rainwater; birds come to drink there, and ripe seeds are loved by goldfinches. Flowering extends from July to September; the terminal branches bear golden-yellow heads 7 to 9cm in diameter. They are composed of numerous ligulate florets, resembling petals, arranged around a yellow heart. Bees, bumblebees, butterflies and hoverflies visit them for their pollen and nectar. The plant tolerates temperatures below –25 °C. The stems are heavy when in flower and can be laid flat by strong winds or a storm. The cup plant self-seeds readily on bare ground; unwanted young plants should be removed early, as their root system quickly becomes difficult to extract.

It is the perfect type of plant to accompany large grasses such as Miscanthus and Panicum in an open, sunny garden. This cup plant can also be paired with other tall plants for moist ground such as Vernonia crinita 'Mammuth' and Persicaria polymorpha, a robust knotweed bearing large white inflorescences in summer. Its cut stems can be used in large country-style flower arrangements, with large daisies, for example. Cut them when the first flowers are open, then remove the lower leaves, which are too bulky and rough.

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