From Tonkin Orchids, Inc., Livemore, California
Temperature and Humidity: The green-leaved types ideally require night temperatures around 50 to 55 oF, while the mottled-leaved types need 60 to 65 oF at night. Day temperatures should range between 70 and 80 oF, although short periods of moderate higher or lower temperatures will not injure the plants. The humidity should be moderate, between 40 and 50 percent.
Light and shade: Paphiopedilums enjoy medium light intensity, requiring 800 to 1,000 foot candles throughout the year for optimum growth. Direct sun, except in the early morning, should be avoided. In the home, move the plants back from the window at the peak of the noonday sun, or ideally grow them behind a filmy curtain.
Air Movement: As with all orchids, moist, vigorous air movement, at a temperature favorable to the plants is highly recommended to keep the leaves cool and to dry drops of water from the plants, thereby reducing chances of disease. Hot or cold drafts will blast paphiopedilum flower buds so be very careful of the position of your plants, particularly on a windowsill.
Watering: Although the growth habit of paphiopedilums is sympodial, they do not possess pseudobulbs. Hence, like phalaenopsis, they must receive regular and constant watering. This will entail keeping the potting media moist but not wet. Perfection of this technique requires some experimentation.
Potting: There are at present many different potting media to choose from. Many of them have been described in various issues of AOS Orchids. Straight fir bark makes an excellent growing medium. Because paphiopedilums are semi-terrestrial, a potting medium that drains well but retains moisture is necessary. Consequently, fine chopped fir bark, commonly called, 1/8 to 1/4 inch, is preferable to the medium to large sized chunks used as cattleya or phalaenopsis potting medium. Be sure that you wet the bark thoroughly before potting any type of orchid in it.
Feeding: Plants in fir bark are fed with a high nitrogen fertilizer, a 3-1-2 or 3-1-1 formula, at one-half recommended strength. For greenhouse growing you should fertilize three times and then use plain water for the fourth watering in order to leach out any salts that have accumulated. For home or windowsill growing alternate the use of fertilizer and plain water.