Cypripedium macranthos, often referred to as the Big-flowered Lady’s Slipper, is a captivating terrestrial orchid. Its unique floral structure and remarkable blooms make it a prized addition to specialized gardens.
Discovering Cypripedium macranthos
Physical Characteristics
Cypripedium macranthos is recognized for its large, showy, slipper-shaped flowers. These blossoms display shades of pink, purple, or reddish-purple, often with darker veins or spots. White-flowered forms are less common. The unique “pouch” or labellum, which gives the orchid its common name, measures about 4.5 to 5.5 cm and functions as a trap for pollinating insects.
The plant grows 30 to 60 cm tall, with an upright, hairy stem. Two to four oval-shaped, green leaves with prominent veins are borne along the stem. Flowers usually appear singly, or sometimes in pairs, atop the stems in late spring to early summer, lasting up to three weeks.
Natural Habitat and Distribution
Cypripedium macranthos is native to temperate regions across Asia, including China, Japan, Korea, Russia, and Taiwan. It thrives in diverse habitats, such as subalpine meadows, forests, woodland edges, and mountainous areas. It grows in cool, shady locations, often under tree canopies, at elevations from sea level up to 2,400 meters. The plant prefers well-drained, humus-rich soils, commonly found in these forested settings.
Cultivating This Lady’s Slipper Orchid
Light Requirements
Cultivating Cypripedium macranthos successfully requires mimicking its natural light conditions. These orchids thrive in indirect sunlight or dappled shade, similar to their native forest understory. Direct midday sun can scorch the leaves, so providing around 70% shade is recommended.
For outdoor plants, a location on the north side of a building or beneath deciduous trees provides suitable shade. Yellowish splotches or browning and curling leaves indicate excessive sun exposure, signaling a need to adjust the plant’s position. Consistent, strong air movement around the plants also helps regulate temperature and light intensity.
Soil and Growing Medium
For Cypripedium macranthos, the soil and growing medium must provide excellent drainage and aeration while retaining some moisture. A suitable potting mix includes two parts clay garden soil, two parts thick leaf mulch, one part sand, and one part cut sphagnum. Other recommended materials include horticultural grit, perlite, and specialized orchid mixes with bark or porous clay particles. The goal is a loose, open mix that prevents waterlogging and root rot. When planting, place the rhizome superficially, with growth buds just at or slightly below the soil surface, ensuring roots are spread naturally.
Watering Practices
Cypripedium macranthos requires consistent and careful watering, preferring moist but not waterlogged conditions. During the active growing season (spring through early summer), water regularly, often a couple of times a week. The soil should never dry out completely, but avoid prolonged saturation.
As the plant approaches dormancy in late summer or early autumn (indicated by yellowing and browning leaves), gradually reduce watering frequency. During winter dormancy, the plant requires very little water, as overwatering can lead to tuber rot. Water loss primarily occurs through the leaves, so the watering schedule should adjust with the plant’s foliage development.
Temperature and Humidity
Cypripedium macranthos is a cold-hardy orchid that prefers cool temperatures. Ideal daytime temperatures during the growing season range from 15-20°C (59-68°F), with cooler nighttime temperatures between 8-13°C (46-55°F). While it can tolerate slightly warmer conditions, temperatures should not consistently exceed 26°C (80°F).
During winter dormancy, these orchids can withstand freezing temperatures, with some sources suggesting they can tolerate conditions as low as -30°C (-22°F). Humidity levels should be 70-80% in summer and early autumn, dropping to 50-60% in winter and spring. In areas with mild winters, good drainage prevents issues caused by excessive winter wetness.
Fertilization
Cypripedium macranthos requires a cautious approach to fertilization due to its sensitivity. Fertilize sparingly, using a balanced orchid fertilizer at a diluted strength (1/4 to 1/2 of the recommended dose). Applications can begin in early spring as new growth emerges, continuing weekly or every 10 days during the active growing season.
Some growers prefer a granular, timed-release fertilizer in spring or alternating liquid feeds with seaweed fertilizer. Avoid chemical salt-based fertilizers, favoring organic blends. Fertilization should cease from October to February when the plants are dormant, as their demand for nutrients is very low during this period.
Common Pests and Diseases
Cypripedium macranthos is not often prone to serious pest or disease issues, but some problems can arise. Slugs and snails are common pests that can damage new, juicy shoots. Preventative measures include using slug pellets, electric fences, or beer traps.
Fungal infections, such as root rot, can occur if the plant is overwatered or grown in poorly drained soil. Proper drainage and careful watering prevent these issues. Regular inspection and good hygiene in the growing area help identify and address potential problems early.
Propagating Cypripedium macranthos
Cypripedium macranthos can be propagated through division, the most practical method for home growers. This involves carefully separating mature clumps, ensuring each new section has healthy roots and a growth bud. The optimal time for division is when the plant is dormant or just beginning new growth in early spring or autumn.
When dividing, handle the delicate root system with care and replant divisions promptly into a suitable, well-draining medium. While seed propagation is possible, it is a complex and challenging process for orchids, often requiring specialized laboratory conditions. Orchid seeds are tiny and lack endosperm, relying on a symbiotic fungus for germination, making in vitro techniques common for commercial propagation.
Protecting Cypripedium macranthos
Wild populations of Cypripedium macranthos have faced significant declines, leading to its listing as endangered in some countries. Its appeal makes it a target for overcollection. Habitat loss due to climate change, deforestation, and urbanization also contributes to the reduction of its natural range.
Given its sensitive status, purchase Cypripedium macranthos only from reputable nurseries that propagate plants through cultivation rather than collecting them from the wild. Ethical sourcing helps ensure demand does not further deplete vulnerable wild populations. Conservation efforts involve both in situ protection of natural habitats and ex situ conservation in botanic gardens.