Paphiopedilums, or slipper orchids to some, originate from the jungles of Southeast Asia and Indonesia. They are semi-terrestrial, growing in humus and other material on the forest floor, on cliffs in pockets, and occasionally in trees. They're easy to grow in the home, under lights, or in the greenhouse.
"Paphs", as we call them, like shady conditions, as in the home in an east or west window, or near a shaded south window. In the greenhouse, heavy shade must be provided - giving them about 1000 to 1500 foot candles. Fluorescent light is excellent; use 2 or 4 tubes just over the leaves.
Since they have no pseudobulbs and store most of their water in their leaves, paphs must have water constantly available at the roots. They need a moist medium - never soggy, but never dry. Water once or twice a week. Humidity should be moderate, between 20% and 30%, which can be maintained in the home by setting the plants on trays of gravel, partially filled with water, so that the plants never sit in water. In dry climates, misting (in the morning only) can help increase humidity. In a greenhouse, average humidity is sufficient; spraying the floor or using an evaporative cooling system in warm climates can increase the humidity. Air movement is essential, especially when humidity is high.
Many growers separate paphs into two groups, the warm-growing mottled-leaf types and the cool-growing, green-leaf types. Warm-growing types should be 60-65 F at night, and 75-85 F or more during the day. Cool-growing types should be 50-60 F at night, 75-80 F during the day. All plants may be grown in the same temperature range with excellent success. The plants can stand night temperatures in the 40s if necessary (as when grown outside in mild climates), as well as temperatures to 95 F. Care must be taken to protect the plants from rot when cold (keep humidity Iow, and do not let water stand on leaves or in the crowns of the plants), and also to protect from burning when hot (shade more heavily and increase humidity and air movement).
High-nitrogen fertilizers (20-20-20) are recommended when potted in any fir bark mix. In warm weather, some growers use full-strength applications every two weeks; others use strength every watering. It's important to flush with clear water monthly to leach excess fertilizer, which can bum roots. In cool weather, fertilizer applications once a month are sufficient.
Paphs should be re-potted about every two years, or as the medium decomposes. Seedlings are often repotted annually. Mixes vary tremendously; most are fine- and/or medium-grade fir bark, with varying additives - perlite (sponge-rock), coarse sand, sphagnum peat moss, etc. Moisture retention with excellent drainage is needed. Divide large plants, by pulling or cutting the fans of the leaves apart, into clumps of 3 - 5 growths. Smaller divisions will grow, but may not bloom as well. Spread the roots over a small amount of medium in the bottom of the pot and fill with medium, so that the junction of roots and stem is buried «" deep in the center of the pot. Do not overpot; an average plant should have a 4" - 6" pot. Here at Orchids of Los Osos, we use approximately 80% fine fir bark and 20% medium perlite.