Slipper Orchids Cast a Spell Over Those Seeking the Unusual

IT SEEMS THAT SPECIES AND hybrids from the genus Paphiopedilum, which are popularly called paphs, are orchids that many growers either adore or loathe. Indeed, some do not regard them as real orchids at all. Despite a lack of little middle ground in their popularity, it is not uncommon for their detractors to become converts as their experience with orchids evolves.

This Asian genus forms the largest part of the orchid group commonly known as “slipper orchids,” so named after the shape of their modified lip, which resembles the rounded toe of a shoe. The alliance also includes the genus Cypripedium, comprising hardy species found in the northern hemi-sphere, as well as the species in the genera Phragmipedium, Mexipedium and Selenipedium, which are natives of the tropical Americas.

There has been taxonomic con-troversy within the genus since the discovery and description of the first plants by European botanists in the middle years of the 19th century. This is due in part to the tendency toward uniformity among locally inbred plant populations, which may or may not deserve to be recognized as a separate species from rather similar plants found elsewhere. Natural hybrids occur within the genus as well, which confuses matters further.

Most experts put the number of Paphiopedilum species somewhere between 60 and 80, yet the debate regarding classification within the genus continues to the present day. New Paphiopedilum species continue to be identified and named as various parts of Asia are more thoroughly explored.

Rather broad diversity among Paphiopedilum species has led most taxonomists to divide the genus into subgenera that are further divided into sections to include closely related species. It is not my intention to describe each of the sections, but a few merit mention.

Section Barbata includes the species that were combined to produce the primary hybrid Paphiopedilum Maudiae (callosum × lawrenceanum), a major contributor to complex hybrids and also the progenitor of those hybrids popularly known as “Maudiae types.” Maudiae paphiopedilums usually have striped dorsal sepals and warted petals. They are known for their ease of culture and include a range of floral variations from the albinistic green and white forms to those popular burgundy blossoms known as vinicolors.

The influential primary hybrid Paphiopedilum Leeanum (insigne × spicerianum) has its roots in Section Paphiopedilum. Paphiopedilum Leeanum is at the base of virtually all of the complex hybrids. Other popular and unique species from this section include Paphiopedilum charlesworthii, Paphiopedilum fairrieanum and Paphi-opedilum villosum.

Arguably the kings of the genus are the multifloral species that hail from Section Coryopedilum. These include such species as Paphiopedilum roths-childianum, Paphiopedilum stonei and Paphiopedilum sanderianum. Well-grown specimens of these paphiopedilum species and their hybrids always command attention and continue to win top awards at orchid shows and AOS judgings. However, the plants of the species in this section tend to be large and are reputedly more difficult to cultivate and successfully flower than are those of some of their slipper-orchid cousins.

Finally, I never miss an opportunity to promote the somewhat florally diminutive species of Section Cochlopetalum. What these sequential-blooming plants lack in flower size is nicely compensated for by their longevity of bloom. They produce their interesting flowers, one after another, on the same stalk for months. The section is closely allied and differences between species are subtle. Look for Paphiopedilum glaucophyllum or Paphiopedilum victoria-regina and you will have an orchid-flower-producing machine that is hard to beat. I have found them of easy culture, too.

The exciting world of paphio-pedilum hybrids commenced with the flowering of Paphiopedilum Harris-ianum (villosum × barbatum) at the Veitch nursery of England in 1869. This triggered a wave of hybridization that has flourished for decades. Recrossing and inbreeding multiple species eventually produced the complex hybrids popularly known as “bulldogs,” which seemed to reach their zenith during the last half of the 20th century.

While a number of variations and breeding milestones were reached over the years, most complex hybrid types fell within a rather tidy range of reddish bronze and/or green and/or white flowers, with or without stripes and/or spots. Perhaps that oversimplifies the accomplishments of the dedicated breeders who produced these re-markable flowers, many of which are still coveted and grown in contemporary collections. Indeed, these hybrids were so round and waxy that it seemed little more could be accomplished with most of the popular breeding lines. Even so, I sense a resurgence of interest in complex hybrid paphiopedilums these days.

Toward the end of the 20th century, with seemingly little left to achieve in complex hybrid breeding, attention turned to crossing the complex hybrids back to traditionally popular Paphio-pedilum species, as well as some of the newer species that had recently come onto the scene. Such breeding resulted in a wave of novelty hybrids in which the progeny not only bear a strong resemblance to their species parent, but also share the positive attributes of their hybrid parent too. This type of breeding continues to dominate paph hybrids today.

Horticulturists tend to think of paphiopedilums as terrestrial orchids — ones that grow in the earth. In fact, many paphiopedilums are lithophytes, which cling to rocks and the traces of thin soil or organic matter that may accompany them. A few species are epiphytes. It is difficult to make generalizations regarding the culture of such a large and varied genus, but here are some.

Since they do not have pseudobulbs, most require a rather moisture-retentive potting mix, yet it must have good drainage. My current favorite for them consists of six parts medium-sized coconut husk chips blended with two parts coarse perlite and one part horticultural charcoal. I formerly used bark chips instead of coconut husk chips, but find that the coconut chips are more durable and moisture retentive.

It is often said that rapidly growing young plants benefit from frequent repotting. This can be particularly important if you use a growing medium that breaks down quickly, since the root system can quickly rot if it is consistently wet. Older plants with multiple growths may be separated into several plants, but keeping them together as long as possible will produce a beautiful specimen with multiple inflorescences.

As with most other orchids, paphio-pedilums generally grow best in a pot rather small for the size of the plant. Many are quite tolerant of lower light levels and make good subjects for indoor culture. Household temperatures suit them too. Most are excellent subjects to grow under artificial lights.

Paphiopedilums are subject to most typical orchid pests and diseases. Paphiopedilum growth habit may make detection somewhat difficult, so take care to look inside and underneath the fans of foliage regularly for signs of trouble. Watch for fungal or bacterial diseases on the foliage and in the crown of the plant, either of which may quickly kill it if left untreated. Such problems can often be prevented if spacing between plants is adequate and attention is paid to maintaining good air movement and avoiding low temperatures.

Paphiopedilums respond well to fertilization but are not greedy. I have come to favor the use of time-release fertilizers in their pots, especially during periods of active growth.

Slipper orchids seem to arouse passions among their enthusiasts in excess of those for any other type of orchid. Maybe the intrigue for the genus is that it includes some of the easiest-to-grow orchids, yet there is plenty of challenge for the more experienced grower too. One of my fellow orchid judges perhaps put it best when she remarked, “Paphs are easy to grow, but difficult to grow well.”