Cloud forest canopies host some of the greatest orchid diversity. I recall a pasture cut out of the cloud forest in Monteverde, Costa Rica named ‘the Bullpen’ where we enumerated more than 75 species within about 10 acres. But epiphytic gardens host many other plants as well—mosses, ferns and fern allies, blueberries or their relatives (Vaccinium spp.), hollies (Ilex spp.), rhododendrons (Asian tropics), and various pitcher plants (Asian tropics). Remarkably bogs in northern latitudes have floristic similarities—the ferns, various Vaccinium species, rhododendrons, hollies, the lone pitcher plant, Sarracenia purpurea, and, of course, several bog orchids. But the similarities are also physical. Bogs and cloud forest canopies usually have a low pH, as low as 3.5 in some bogs and both are low in nutrients. This is why trees growing in bogs are runty with extremely low growth rates, while those of forest canopies rooted in mineral soil are usually not stunted. Finally, moisture is evenly distributed in cloud forests which screen moisture directly from clouds as well as in bogs floating with fluctuating water levels. Perhaps a bog may be viewed as a temperate climate canopy at ground level, but are these comparisons useful, especially for growing orchids and seeking alternative potting materials in a world where traditional materials can become scarce?
In the nineteenth century European growers used sphagnum moss from bogs and moors as a potting material, a practice recently revived and a subject of a previous Selby Vignette. Another bog plant (although not exclusively so) is osmunda, a favored orchid potting medium before the advent of barks in the mid-twentieth century. But most of us have little experience with osmunda, so what is it and how does it work as a potting medium?
First, osmunda root comes principally from one of three species in the United States, Osmunda cinnamomea or cinnamon fern. It is harvested from old fern colonies where the root continues to accumulate in extensive mats. In nature, it often raises the crown on a sort of trunk as in a tree fern. Extensive mats are need for harvesting osmunda fiber productively.
Rebecca Northen (1970) spoke of its virtues: “Its fibers are tough and springy so that they give the roots plenty of air, yet in the process of decay it furnishes all the nutrients the plants really need.” Orchids in osmunda didn’t require fertilizing, although they were reported to benefit from dilute fertilizer applications, and it lasts a long time in good condition. She continues to say, “potting with it is a slow process requiring a strong arm.” Not only were cattleyas potted in osmunda but also paphs, although Northen indicates that most growers would add sphagnum for moister retention. Finding bark mixtures in local garden centers is difficult where orchid growing is an uncommon practice, so I have been experimenting with the local wild osmunda.
We have large colonies of cinnamon fern available in a local wet land. Unlike a true bog where the substrate is organic peat from eons of accumulated dead plants, this wetland has a mineral soil substrate. Although it makes for a pleasant outing, harvesting and preparing it from habitats with mineral soil is time consuming requiring a sharp shovel and extensive washing to remove the mineral soil. Once cut out of the ground it must be cut into chunks with careful removal of any snails or companion plants such as sedges that otherwise benefit from the attention we would normally give the orchid. Potting with it is not particularly difficult, but unlike bark mixtures its springy texture requires fairly hard packing that used to be accomplished with a potting stick, otherwise top-heavy orchids can rock thus causing root damage. It is amazing how much osmunda one can tamp into a single pot!
I have tried several Laelia purpurata and two paphs in pure osmunda with the following results. While I usually find L. purpurata resents being repotted in bark mixtures, they seem to rebound more quickly in osmunda with strong root growth. Being somewhat more moisture retentive may be a factor in success with it. Laelia anceps also performs well in it, although not remarkably more so than in bark mixtures. Growing paphs in it is trickier requiring less tight packing to preserve the fleshy roots, a practice resulting in a more porous medium. I found that unless I religiously watered the plants (P. Maudiae ‘The Queen” and P. venustum) daily, root growth stops. Addition of sphagnum to the mix may solve this problem.
So what is osmunda? Osmunda ferns (common name) include about 10 species from the genus Osmunda (scientific name) with three species in the United States (Tryon and Moran 1997). The cinnamon fern occurs over the eastern United States and adjacent southern Canada south into Florida and west to New Mexico and the Dakotas. As with so many ferns that disperse by means of spores, it is also known from eastern Asia, the Himalayas, Andean South America, Guyana and Brazil. It is a relatively common fern, so some orchid growers may have a ready supply. The other two species in North America include the royal fern (Osmunda regalis) and interrupted fern (O. claytoniana). The royal fern occupies much of the same range as the cinnamon, but also includes most of Europe and parts of Africa. The interrupted fern also has a similar range in North America, although it ventures farther north, and is absent from the extreme Southeast. Neither interrupted nor royal ferns produce the extensive root mats of the cinnamon fern. I once tried harvesting royal fern, but the less dense root fibers held proportionally more soil and was much more difficult to clean with less fern root resulting from my labors. I have no experience with osmunda derived from the interrupted fern, but it is a common fern locally of many habitats.
Cinnamon fern occurs in a broad range of habitats including old pastures, but should be harvested without harming natural colonies, and only on your own property or by permission of the owner and never in public parks. Although bogs would probably provide easier cleaning, we cannot recommend harvesting from these delicate habitats, even if you own the property. This communication promotes its use because of its ubiquity in often-secondary habitats.
With possible fluctuation of bark supplies and conservation concern for tree ferns, perhaps we should seek more alternative potting materials taking our cues from the environment. My Paphiopedilum St. Swithin potted in pure limestone chat (purchased from a cement company) with a trace of fern root recently produced six flowers on one stalk as a houseplant. Both the parents of P. St. Swithin grow naturally rooted on the sides of cliffs of uplifted seabed, so my success with it may not be surprising. I grow P. St. Swithin with the pot hanging and tipped toward the light, as its parents would grow in nature.
There are many more native ferns available other than osmunda with dense root masses of which I have no experience, and there are rumors that some of the true mosses also provide useful orchid substrates. In experimentation, orchids need to be watched carefully especially for root growth since some substrates inhibit growth as I learned in the case of a live unidentified species of Sphagnum from the Florida Panhandle. I would guess that this species inhibits vascular plants that would otherwise out-compete it for light. Whether selecting potting materials or growing orchids in a sunny window or greenhouse, we always benefit by taking our cues from the habitat.
Literature CitedNorthen, R. T. 1970. Home Orchid Growing. Van Nostrand Reinhold Co. New York, NY 10001. 374 pp.
Tryon, A. F. and Moran, R. C. 1997. The Ferns and Allied Plants of New England. Massachusetts Audubon Society, Lincoln, Massachusetts. 325 pp.