Paphiopedilum charlesworthii alba 'Japan' is a selected alba form of Paph. charlesworthii, offered in Potsize 8 cm and depending on the chosen variety with or without flowering. The SM/JOGA designation refers to a Silver Medal within JOGA's prize system.
Origin
Paphiopedilum charlesworthii, according to Kew, has a natural distribution from Assam (Mizoram) and western Yunnan to Myanmar and Thailand and belongs to humid tropical biomes.
In the literature, this species is described as both epiphytic and (semi-)terrestrial, which explains well why in culture it usually performs best in an airy but evenly moist substrate.
Characteristics
This is a medium-sized Paphiopedilum with glossy, strap-shaped green leaves that can reach about 25 cm in length when mature. The flowering stem arises from the center of the rosette and, in this species, usually bears one flower of about 8 cm, with a good vase life.
The "standard" charlesworthii is known to have a lime green, brown-veined pouch with a contrasting, often white to pink-veined upper cuttlebone. In the alba form, pigmentation is markedly reduced, making the upper petals appear much whiter and the pouch more often remains green.
Care
Light
Filtered light or semi-shade suits best, with protection from direct sunlight in spring and summer. In winter, the location can actually be lighter, as long as the leaves do not heat up behind glass.
Temperature
An intermediate range is usually the most stable. Values around 20-25 °C in summer and 18-22 °C in winter are mentioned by RHS for this species. Protection from cold is important, especially in combination with moisture in the heart of the plant.
Substrate
A bark-based Paphiopedilum mix with good drainage and at the same time sufficient moisture buffer fits well. A combination of fine bark with some sphagnum and other organic structural supports often works predictably, as long as the substrate remains airy and does not silt up.
Humidity
Moderate humidity is usually sufficient, roughly around 40-50%, with air movement as humidity increases. Misting on the leaves is not recommended at Paphiopedilum; a bowl of damp pebbles works better to provide some support for the environment.
Nutrition
Regular, mild feeding during the growing season works most consistently. Guideline is once every two to three weeks and markedly quieter in winter. Flushing the medium periodically helps reduce salt buildup.
Watering
The medium should remain moist, but not soaking wet. Letting it dry slightly between waterings is fine, but prolonged complete dryness does not suit Paphiopedilum as there are no pseudobulbs to buffer water. Excess water should always be allowed to drain away.
Preferably use demineralized water, especially if the tap water is hard, and flush occasionally to avoid accumulation of salts.
Repot
Repotting can be done when the substrate visibly breaks down or the pot becomes too tight. As a guideline, it is often mentioned about every two years, and preferably after flowering or in the growing season when new root activity gets going.
Flowering
For Paph. charlesworthii a flowering period in summer to fall is mentioned, usually with one flower per stem. The flowering period is often long in slipper orchids, and can last for weeks or even months under good conditions.
