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Silphium perfoliatum AGM

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© RHS

Characteristics

Plant type

Herbaceous Perennial

Habit

Bushy

Fragrance

Leaf

Resilience

Hardiness

H7 (very hardy)

Colour

Flower

Yellow in Autumn and Summer

Foliage

Green in Autumn, Spring and Summer

Size

Ultimate height

1.5-2.5 metres

Ultimate spread

0.5-1 metres

Time to ultimate height

2-5 years


Preferred common name

cup plant

Family

Asteraceae


Silphium are robust herbaceous perennials with tall stems bearing simple leaves, aromatic when bruised, and loose clusters of yellow, daisy-like flowers in summer and early autumn

S. perfoliatum is an upright perennial to 2.5m tall, with paired, oval leaves joined around the stem, and branched sprays of bright yellow daisies 7-9cm wide, opening in late summer

Other common names

  • cup rosin weed
  • Indian cup

How to grow

Sunlight

  • Full sun
  • Part shade

Aspect

  • South-facing or West-facing
  • Exposed or Sheltered

Cultivation

An impressive plant suitable for the back of a border. It performs best when grown in full sun; in partial shady, or windy, sites it may require staking

Soil

  • Well-drained or Moist but well-drained
  • Acid, Alkaline or Neutral
  • Loam

Propagation

Propagate by seed or division

Suggested planting locations and garden types

Architectural, Cottage/Informal Garden or Flower borders and beds


How to care

Pruning

Cut back after flowering; stems may optionally be left until shortly before new growth begins the following season

Pests

Generally trouble free

Diseases

Generally trouble free