The Slipper Orchids, particularly Paphiopedilum (Paphs) and Phragmipedium (Phrags), have held the attention of discriminating collectors for more than a century. Although most interest has been in modern hybrids of the genus Paphiopedilum, nearly as much enthusiasm has been evidenced in selected species and new introductions. The other two genera in this alliance are Selenipedium and Cypripedium (Cyps). Regardless, one can always find room in his collection for these attractive plants with glossy and/or mottled foliage which produce long-lasting flowers. Available in species and hybrids which produce flowers in white to red with variously colored highlights, there is something for everyone. The species of Paphiopedilum come from a huge area in the Old World, including India and China through Indonesia and the Philippines to New Guinea, while species of Phragmipedium are found from Mexico to Brazil. Selenipedium are found in tropical South America, while the Cyps inhabit temperate North America. All genera are threatened in their habitats and therefore forbidden from importation under existing C.I.T.E.S. regulations. The Cyps are protected under Federal and state regulations in the U.S.
Realize that these instructions are necessarily general and should be adapted to the cultural environment in which you are growing. Of course, specific cultural requirements peculiar to the type can be determined by review of available reference material such as that suggested below under the heading Recommended Reading.
Paphs require somewhat more shaded but otherwise similar cultural conditions to those of Cattleyas. None of the paphs should be kept wet nor should they be watered in such a way as to cause the accumulation of moisture in their crowns. Phrags, on the other hand, are reported to thrive in standing water setups, but no moisture in the crowns.
Not only are paphs attractive to beginners because they are compact, attractive plants, but also because they can be grown successfully without any specialized facility. Light requirements can be adequately satisfied on a window sill where early morning (until 9:30-10:00 am) sun hits the plant directly. Then, the plant will tolerate medium light intensity (slightly more shaded than cattleya conditions) for the balance of the day. As always, light intensity and temperature are related; the hot mid-day or afternoon sun will provide terrific light, but will also cause the leaf temperature to soar, with resulting burns. Use care in selecting the appropriate window sill.
There are two groups of paphs with respect to temperature requirements. These are 1) warm growing or mottled leaf types which prosper with night temperatures in the 65-68°F.(18-20° Celsius) range, and 2) cool growing or green leaf types which like nights of 50-55°(1O-13° Celsius), ideally. However, most green leaf types have been adapted to grow in much warmer environments than the ideal. In either case, day temperatures should not exceed 80-85° °F.(21-24 ° Celsius). Although plants will not die when exposed for short periods of time to even higher or lower temperatures, their growth is usually adversely affected.
HUMIDITY, AIR CIRCULATION, AND WATERING
Paphiopedilums are relatively slow growing, non-bulbous sympodials with nominal facility for water storage. Therefore, the humidity must be kept high (50-60%) to keep transpiration (leaf water loss) at a minimum. If low humidity is a problem. watering and misting are effective ways of increasing humidity. Care must be exercised to avoid accumulating excess moisture in the crowns. Wet crowns encourage bacterial and fungal activity which may cause a rot with subsequent plant loss. Try hosing down the growing area, i.e. wood bench surfaces, walks and under-bench spaces to effectively increase humidity without actually wetting the plants themselves.
In the home, humidity can be increased in several ways. A commercial humidifier may be used with good results, or shallow pebble trays filled with water may be placed in the growing area. Set the pots on the pebbles, keeping the water below the bottom of the pots. Paphs will thrive in a Wardian case, too, if one is available. Watering should be done as frequently as is necessary to keep the medium moist. Since there are many possible media to consider, each with a different consistency, from terrestrial to epiphytic, no set schedule can be specified here. However, remember that the more porous a medium actually is, the more quickly it will dry out. Also consider the potting container; a clay pot breathes, while a plastic pot does not. Any medium in clay pots will dry out more quickly than will the same medium in a plastic pot. See other notes on watering under the heading Fertilizer.
POTTING MEDIA. CONTAINERS. AND REPOTTING
A variety of containers may be used for paphiopedilum culture. However, the two most frequently utilized are clay and plastic pots. As mentioned in the previous section, the basic difference culturally in the two relates to the rate at which they dry out. Hence, the grower must adjust his watering practices accordingly.
The medium in which paphiopedilum species grow in nature is basically humus. Therefore, the medium used in cultivation should not be too dense, to allow for circulation of air through the medium. Try a generic mix comprised by volume of 4 parts fine fir bark, 3 parts medium-coarse shredded tree fern, 1.5 parts coarse perlite, 1.5 builder's sand, plus one-half pound of dried cow manure in each cubic foot of mix. The resulting medium is well-drained and has excellent nutrient retention characteristics. New Zealand sphagnum moss with fine hardwood charcoal is also been used. Rockwool, an inorganic medium, and peat based mixtures, such as ProMix BT® are being used with great sucess. However, one must be certain that the soil reaction (pH) of the mix is basic. If necessary, add dolomitic limestone as a top dressing on the medium in the pot to increase the pH to approximately 8.
Repot paphiopedilums only during periods of growth. Select plants to be handled when a new growth emerges from the side of the existing plant to insure that the plant will continue its vegetative growth cycle with a minimum of setback.
Paphiopedilums have sensitive roots, often few in number. Therefore, one must be extremely cautious in taking a plant out of a pot to change the medium and/or container. Each root is covered with tiny hair-like structures which are effective water gatherers. Do not be alarmed if plants just repotted do not show signs of adjustment for several weeks. This is normal and to some degree is a function of how carefully the plant was handled in the process.
FERTILIZERDuring the growing season, use 20-20-20 soluble fertilizer every 10-14 days at the rate of 1 teaspoon to a gallon of water. Remember that the roots of paphiopedilums are negatively sensitive to excess salts in the medium. Be certain to leach thoroughly between fertilizer applications to minimize the accumulation of salts which can cause root tip burn. Reduce frequency and rate of fertilization during the periods of reduced temperature and shorter days (November-March) in the northern hemisphere.
Again, the need to keep plant crowns dry is emphasized. Should rot occur, cut away the rotted area. Then treat the affected plants with a Physan solution prepared at a dilution rate of one teaspoon/gallon of water. The chemical may be poured into the crown or onto the potting medium surface. A Dithane M45 paste placed on the cut has also been very effective. A Dithane M45 at a dilution rate of one teaspoon/gallon has been extremely effective, in preventing rots, when sprayed in to healthy crowns.
Resist the temptation to move plants about after a flower stem and bud have appeared. Stake the stem as necessary while it is developing, but do not move the plant or a twisted, crooked inflorescence will result.====RECOMMENDED READING ====
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