The Slipper Orchid Alliance


By Marilyn LeDoux, Windy Hill Gardens, Labadie, MO

[Reprinted from Fall 2000 SOA Newsletter]

Phragmipediums are New World ladyslipper orchids that grow from Mexico through central South America. Most are terrestrial (grow in the ground) or lithophytic (grow on rocks), but a few species can sometimes be epiphytic (grow on trees). The tree dwellers are primarily the long-petaled caudatum types. Some species prefer to grow in the splash zone of waterfalls and on streambanks and can often be submerged during periods of heavy rain. These streams and waterfall dwellers include the species caricinum, kaieteurum, klotzschianum, lindleyanum, longifolium, pearcei, and sargentianum. Phrags flower at various times but most heavily in the late winter and spring. Mature plants of many sequential-blooming species can be in bloom for six months or more.

Light. Light needs for Phrags range from bright (cattleya-like, 3,000 to 4,000 footcandles) for the long-petaled caudatum types and xerophyticum, to medium low (Phal-like or mottled leaf Paph-like, 1,500 to 2,000 footcandles) for besseae and schlimii.

Growing these lower light Phrags on a lower bench in a greenhouse usually provides both the reduced light levels and somewhat cooler temperatures they prefer.

Temperature: Most Phrags prefer intermediate temperatures with nights in the upper 50's to the mid 60's. However, besseae and schlimii can tolerate and even prefer somewhat cooler temperatures. If kept much cooler in the winter, keep them somewhat drier as well, not soggy wet. Phrag xerophyticum prefers temperature on the warmer end of the ranges given above.

Humidity and air circulation: Grow in humidity above 50 percent if at all possible. Plant groupings on pebble-trays with water between the pebbles is very helpful when growing in the home. Caudatum types are most tolerant of less humidity, as long as the roots remain moist. Constant air circulation, especially in a greenhouse or grow room is very important. In higher humidity growing areas such as these, growths that do not dry out by evening can develop a bacterial rot. Constant air circulation can help prevent this problem. If a problem does occur, pull off the infected leaves and use a bactericide. This problem can occur on any Phrag but is most prevalent on caudatum types and their hybrids.

Water: Good quality water is very important for growing Phragmipediums. Tap water with low dissolved solids is OK, but rain water or reverse osmosis (R.O.) water is usually even better. Flush the media and roots well each time you water. Most Phrags should be kept moist at all times; however, the caudatum types and xerophyticum can become somewhat drier between waterings. Some people have great success growing their moisture-loving Phrags sitting them in saucers of water. To help prevent bacterial rot problems do not water over the tops of the plants on cool, cloudy days if the growths will not dry out by evening.

Fertilizer: In general, Phrags can take more fertilizer than Paphs, but feeding too heavily can cause leaf tip burn. When using rain or R.O. water be sure to use a fertilizer with essential micro-nutrients, such as Dyna-Grow. I prefer using water-soluble or liquid fertilizers at one-fourth to one-half the recommended strength for three or four waterings then flushing thoroughly with clear water every fourth or fifth watering. Less fertilizer and/or a blossom booster (higher phosphorous) fertilizer should be used in the fall and winter.

Repotting and potting media: Repot every one to two years in fresh mix. The best time is usually right after flowering, but Phrags are very tolerant of repotting anytime. I prefer the following basic potting mix for my phrags:

* 9 quarts fine bark (Sequoia).

* 3 quarts perlite or sponge rock.

* 3 quarts fine to extra fine charcoal (#3 or #4)

* 3 quarts fluffed Canadian peat or Pro-Mix HP (or similar peat-based mix).

* 1/ 2 cup bone meal.

For phrags (excluding xerophyticum) potted in 5-inch and larger pot sizes, I like to add in 1/4 to 1/3 medium sequoia bark. I also often add in 1/4 fluffed rockwool, especially for the more moisture-loving types of phrags. I never use rockwool in my xerophyticum mix.

For Phrag (Mexipedium) xerophyticum, I add to the above formula:

* 1/4 cup dolomitic lime.

* 1/4 more charcoal for good drainage to any size part of this mix separated out. For example, for two cups of the above mix, I add  cup or more of extra fine charcoal.

I also use the above mix, minus the extra charcoal but with the dolomitic lime, for my paphiopedilums. I also like to use styrofoam peanuts in the bottoms of my pots for good drainage.

Happy Growing!