Cup plant

Sun

Full sun is best; tolerates light shade, but stems may lean and flowering may decrease.

Water

Prefers consistently moist ground and tolerates occasional flooding. Established plants withstand short dry spells, but prolonged drought can scorch the lower leaves.

Soil

Moist, reasonably fertile soil, including clay; tolerates a broad range of soil pH. Avoid very dry, shallow soil.

Height

4-8 ft (1.2-2.4 m)

Spread

2-4 ft (0.6-1.2 m), gradually wider where allowed to spread

Flowers

Mid-summer to early autumn; branching clusters of yellow, daisy-like flowers.

Foliage

Large, rough-textured green leaves in opposite pairs, with upper pairs fused around sturdy, square stems.

Growth

Fast once established

Care needed

Medium

• Pollinators
• Cold hardy
• Heat tolerant
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Very tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   4 ft (1.1 m)

3. After 2 years

   6 ft (1.8 m)

   full size

About 2 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Native to

the US and Canada

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Fast

• Water deeply during the first growing season and during prolonged dry spells.
• Apply a thin layer of compost in spring; avoid heavy feeding, which encourages weak, floppy growth.
• Mulch around young plants to conserve moisture, keeping mulch clear of emerging shoots.
• Install supports in late spring if the site is exposed or partly shaded.
• Remove unwanted seedlings early and divide expanding clumps in spring when necessary.

Pruning. Leave stems standing through winter for structure and wildlife, then cut them to near ground level in late winter or early spring before new shoots develop. Where self-seeding is a concern, remove flower heads before the seeds ripen instead.

Late winter

Cut down old stems before new growth starts, unless they were removed earlier to prevent seeding.

Spring

Plant or divide clumps, water thoroughly, and apply compost and mulch.

Late spring

Thin unwanted seedlings and install supports where needed.

Summer

Water during extended dry weather and check crowded foliage for mildew.

Late summer

Remove fading flower heads before seeds ripen if spread needs controlling.

Autumn

Where spreading is acceptable, leave seed heads for birds and standing stems for winter interest.

• Place at the back of a large sunny border, where its height will not shade smaller plants.
• Combine with tall native grasses and late-flowering perennials for a prairie-style planting.
• Use in a spacious rain garden or beside a pond, above permanently submerged ground.
• Plant in broad groups to create a seasonal screen and a strong vertical backdrop.

Garden styles it suits: Native meadow, Midwest prairie, New perennial (prairie), Wildlife garden, Pollinator garden and Wildflower.

Plant it with: Joe-Pye weed, Swamp milkweed, New England aster, Switchgrass, Ironweed and Oxeye sunflower.

Wildlife: Flowers provide pollen and nectar for bees and other insects, and the seeds feed birds, including finches. Leaf cups hold temporary pools of rainwater used by insects and sometimes birds.

• Powdery mildew can affect crowded or drought-stressed plants; improve air circulation and water the soil during dry spells.
• Rust may cause orange-brown spots on leaves; remove badly affected foliage and clear infected debris.
• Aphids sometimes cluster on young growth; wash them off with water and encourage natural predators.
• Stems may flop in shade or overfed soil; provide more sun, avoid rich feeding, and support stems early.

Not known to be toxic to people, cats, dogs or horses, and no particular poisonous part is established. Species-specific safety information is limited; it is not a food plant, so discourage eating it.

Where it spreads. Can spread aggressively by seed and short rhizomes in moist, fertile gardens. It is listed as invasive and prohibited in Connecticut and New York, outside its native range; check local restrictions before planting.

• Rosinweed (Silphium integrifolium)

  Also has yellow flowers and opposite leaves, but the leaf bases do not join around the stem to make water-holding cups.

• Compass plant (Silphium laciniatum)

  Has deeply divided leaves, especially near the base, rather than broad opposite leaves fused around the stems.

• Prairie dock (Silphium terebinthinaceum)

  Has very large basal leaves and tall, mostly leafless flower stalks, rather than leafy stems with paired cups.

The common name refers to the rain-catching cups formed by joined leaf bases, while perfoliatum describes the appearance of stems passing through the leaves.

Propagation. Divide clumps in early spring, retaining roots and several shoots on each division. Sow seed outdoors in autumn for natural winter chilling, or cold-moist stratify seed before spring sowing; seedlings may take several years to flower.

Accepted botanical name

Silphium perfoliatum

In the US and Canada

Native in Canada and the lower 48 states.

Native range

Alabama, Arkansas, Connecticut, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Masachusettes, Michigan and Minnesota.

Measured

Soil pH 4.5 to 7.5. Average height 178 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.