John T. Atwood, Former Orchid Curator
Orchid Identification Center, Marie Selby Botanical Gardens, Sarasota, Florida
Asking growers about the merits of using sphagnum as a potting medium can elicit varying responses—some positive and others negative. Recently Wilella Stimell of the Orchid Society of Arizona inquired about the quality of New Zealand sphagnum in comparison to that from Chile. I couldn’t give her a quick answer because of the complexities relating to the subject. What are the species of sphagnum being used? Does live sphagnum behave differently from dried? Is orchid growth in sphagnum affected by ambient temperatures, water quality, fertilizer applications, and if so how?
Of the several wild sphagnum species being collected, not all are equally useful. Chilean and New Zealand sphagnum are dried and sold in bails. I have little experience with dried sphagnum but a number of years ago, experimented with live sphagnums collected from the wild.
My experimentation with sphagnums began in 1973 because of a desire to mature a single Phalaenopsis. The white P. amabilis-type seedling planted in a traditional bark mixture had produced but a single leaf per year with each leaf somewhat smaller then the last. With nothing to lose, I followed recommendations in Veich’s Manual of Orchidaceous Plants, and Williams' Orchid Growers Manual, and collect sphagnum from a local bog (then on Cape Anne, Massachusetts). After potting it loosely, I placed the plant in a skylight. The results were phenomenal with at least three leaves produced annually, each larger than the previous one. The local water supply was from abandoned granite quarries and had low mineral content. I recall feeding the plant regularly but dilutely for fear of killing the fertilizer-sensitive sphagnum
Several years later, I moved to Tallahassee from Michigan to work with Norris Williams. The slipper orchid collection I was growing for my research had produced few roots in the new environment. I collected a native species of sphagnum (identified as Sphagnum tenerum), again with phenomenal results. The species of Paphiopedilum sect. Barbata responded best. Paphiopedilum acmodontum produced three and four shoots from a single flowering shoot, and the pot filled with roots. Paphiopedilum philippinense, which that usually dries out severely in nature, did not respond well in it, although P. hennisianum, which grows with it in the wild, did. Most phragmipediums (except the Phragmipedium caudatum complex) also responded with rapid growth. Spherical colonies of cyanobacteria also developed in the pots, as the plants continued to thrive. The sphagnum however died within about six months, after which orchid roots no longer thrived. Repotting in live sphagnum returned the plant to rapid growth. The need for repotting twice a year, a laborious process when maintaining more than a few plants, was the major drawback to growing in live sphagnum.
I discovered though that not all sphagnums are beneficial. I tried a second species with purple-black “stems” from the Tallahassee area with dramatically contrary results. Growth of plants potted in this species (I couldn’t identify it) simply stopped––no roots, shoots, or flowers. I continued using the species I identified as Sphagnum tenerum until I left for Selby Gardens. I tried growing phrags in this sphagnum in Sarasota, but with less encouraging results, perhaps because of the poorer quality of the water.
Although live sphagnum worked for me in Massachusetts and Tallahassee, high water quality with low salt content probably contributed to success in both regions. So what does this tell us about dried New Zealand and Chilean sphagnums? Although sphagnum is purchased in the dried state, it is composed of many species, some of which may be deleterious to plant growth. Perhaps substances produced in some sphagnums inhibit the growth of plants that would otherwise shade them out, but whether they retain their growth inhibiting qualities after drying is unknown. As far as I am aware, commercial collectors of sphagnum do not discriminate among the different species. Clearly if we are to understand effects of sphagnum species from different locations and differing water qualities, quantitative research is needed. In short, the only advice I can offer readers is to try different kinds of sphagnum, even locally collected ones, if they can be legally gathered.
Sphagnum has a long history of use. Both the Amerindians and Celts used it as a poultice for wounds. Not only is it reportedly more absorbent than cotton, but also it has antiseptic qualities. The English used it in the 19th century, because it promotes excellent root growth and inhibits rot, while retaining both water and air. It often is associated with cyanobacteria, which may provide constant low levels of nitrogen. Although some species of sphagnum are rare, others are widespread and among the most common plants in the world. Their ease of propagation and rapid growth should render them fruitful subjects for farming in wetter and cooler parts of the earth. As a renewable resource, beneficial species of sphagnum might be profitably farmed, if carefully developed with species selected for ease of production and perhaps disease resistance. Many species grow in boreal forests. North Florida has about 30 species with which to experiment. Sphagnum tenerum, which I selected, was odd in that it grows in the higher, dryer portions of the flatwoods. I selected this species thinking that it could withstand more drought than those growing closer to the water’s edge.
Handling sphagnum carries some risk of the fungal infection called sporotrichosis (see webpage for the Center for Disease Control; ">http://www.cdc.gov/ncidod/dbmd/diseaseinfo/sporotrichosis_g.htm). Apparently the fungus, Sporothrix schenckii, occurs all over the world, so handling sphagnum carries with it a risk, even if limited. This fungus is also found in the soil, in bailed hay, and even on rose bushes. According to the CDC, “The first symptom is usually a small painless bump resembling an insect bite. It can be red, pink, or purple in color. The bump (nodule) usually appears on the finger, hand, or arm where the fungus first enters through a break on the skin. One or more additional bumps or nodules that open and may resemble boils follow this. Eventually lesions look like open sores (ulcerations) and are very slow to heal. Cases of joint, lung, and central nervous system infection have occurred but are very rare. Usually they occur only in persons with previous disorders of the immune system.” Symptoms usually do not occur until at least one week and sometimes 12 weeks after infection. According to the CDC, persons at greatest risk include plant nursery workers handling sphagnum, rose gardeners, children playing on baled hay, and greenhouse workers handling bayberry thorns. Prevention includes wearing of gloves and long-sleeved shirts.” Although incidents of sporotrichosis are not high, suspected symptoms should be taken seriously as the disease is progressive.