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Cypripedium acaule

pink lady's slipper

Orchidaceae Eastern North America

Attracts Pollinators

Native to North America

SunPart Shade – Full Shade

WaterMedium

HardinessZones 3–8

Overview

Cypripedium acaule is a terrestrial orchid native to eastern North America, growing 6-15 inches (15-40 cm) tall. Two broad, elliptic, strongly ribbed leaves rise directly from the ground, with no leafy stem between them, and a single flower is borne on a separate leafless stalk. The flower has a large, drooping, pink pouch-shaped lip 1.2-2.4 inches (3-6 cm) long, with a vertical slit down the front, framed by greenish-brown twisted petals and sepals. Bumblebees enter the pouch through the slit and exit past the pollen, which is how the flower is pollinated, though it gives no nectar reward. The species grows in acidic soils of pine and oak woods, sandy slopes, and bog edges, and depends on a specific soil fungus to germinate and sustain its roots. This dependence makes wild plants nearly impossible to transplant, and dug plants almost always die. Plants are slow to mature, taking several years from seed to first flower, and may live for decades once settled. The glandular leaf hairs can cause a skin rash like that from primulas in sensitive people.

Native Range

Native to eastern North America, from Newfoundland and the Northwest Territories south through the Great Lakes and Appalachians to Georgia and Alabama. It grows in dry to moist acidic woodlands, on sandy or rocky slopes, and at the edges of bogs.

Suggested Uses

Grown only by specialist native-plant and orchid enthusiasts in acidic woodland or bog gardens, using nursery-propagated stock. It suits undisturbed shaded sites that mimic its native pine and oak woods. Wild collection has reduced many populations, so it is protected in parts of its range.

How to Identify

Recognized by a pair of large, ribbed basal leaves and a single nodding flower on a leafless stalk. The flower has an inflated pink pouch with a lengthwise central slit, unlike other lady's-slipper orchids whose pouches have a round opening. Most flowers are pink, though white-flowered plants occur occasionally.

Appearance

Size & Dimensions

Height6" - 1'3"

Width/Spread8" - 1'

Reaches mature size in approximately 5 years

Colors

Flower Colors

pink

white

Foliage Colors

green

Bloom Information

Bloom Period

~3 weeks

Spring

Flowers in late spring, generally May to June, with one bloom held above the leaves on each flowering plant. Queen bumblebees are the main pollinators, drawn into the pouch by scent and color. Not every plant flowers each year, and a ripe seed capsule may release thousands of dust-like seeds.

Detailed Descriptions

Flower Description

Pink, rarely white

Foliage Description

Green

Growing Conditions

Sun Requirements

SunPartial Shade SunFull Shade

Requires 2-5 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range4.0 - 5.0(Acidic)

357912

Soil Types

peat sand loam

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

Several years from seed to first flower

Care & Maintenance

Care Guide

Grows in part to full shade in moist but well-drained, strongly acidic soil with a pH of about 4.0 to 5.0, rich in pine or oak leaf litter. Depends on specific soil fungi, so it resists ordinary cultivation and rarely survives transplanting from the wild. Where it is grown, it needs an undisturbed, acidic, humus-rich root zone and steady but not soggy moisture. It is slow to establish and declines if the roots are disturbed once settled. Nursery-propagated plants adapt far better than collected ones.

Pruning

No pruning is needed or advised. The two leaves and flower stalk die back on their own in late summer or autumn. Leaving the natural leaf litter in place protects the shallow roots and their fungal partners.