Bringing Ex Situ Orchid Conservation to the Home Garden

Authors


Growing Hardy Orchids . Tullock, J. 2005 . Timber Press , Portland , OR . 244 pp . $29.95 (hardcover) . ISBN 0-88192-715-5 .

Hardy terrestrial orchids are commonly considered to be delicate, fragile plants, tenuously existing in a world of tougher vegetation. Common warnings against attempts to propagate these orchids claim that they are unadaptable to horticulture. This reputation is probably a reaction, understandably so, to many decades of exploitive destruction in the wild for the horticultural trade. Nevertheless, in the context of modern, widespread habitat destruction, this view requires revision, allowing an examination of how modern horticulture can benefit their conservation. Although it is true that some species would not favor artificial propagation, many others are actually quite tough and adaptable. This book provides a refreshing perspective on orchid conservation. The author shows not only that many hardy orchids can be grown in home gardens without ethical or legal violation but also convincingly demonstrates that this can be done by any diligent grower without too much difficulty, thereby bringing orchid conservation into the hands of the general public.

The author, John Tullock, is a long-time conservationist with extensive experience in growing wildflowers. The book starts with a passionately expressed personal view about native orchid conservation. Several illustrative examples are provided in which neither law nor tinkering with the marketplace much affected biodiversity preservation, but preserving habitat and species within a local community worked very well once people were given the tools and incentives for this. Home gardens sometimes have an unanticipated role to play here. In Great Britain the population of the Eurasian yellow lady's slipper (Cypripedium calceolus) dwindled to just one wild plant. With the help of seeds and pollen provided by British gardeners, the species has a chance to survive. That this is still an uncommon practice is caused by the fact that most wildflower field guides and gardening books strongly discourage growing native orchids. In these books native orchids are usually described as difficult to grow and impossible to propagate, making all nursery stock suspect of being derived from illegally collected material. The latter view is outdated, and a handy list of nurseries at the end of the book convincingly shows that legally propagated native orchids are nowadays widely available.

In subsequent chapters more detailed information is given about growing hardy orchids. The pH and moisture content of the growing media and sun exposure and nutrient availability of ideal growing sites are discussed in detail, followed by ways of propagation and transplantation after dormancy. In the chapter on mycorrhizal associations, it is expressed that mycorrhizae are unnecessary for the survival of cultivated hardy orchids once they have reached the adult phase. Neither the author nor the references he cites, however, seem to provide any experimental support that mycorrhizal fungi are actually not present on the roots of cultivated temperate orchids. We doubt that just because an orchid can be grown in sterile media under laboratory conditions it therefore does not need a mycorrhizal associate in the garden. There is abundant evidence in the scientific literature (e.g., Smith & Read 1997) of the widespread association of mycorrhizae and the majority of vascular plants in a huge diversity of habitats; many species of plants in cultivation are known to greatly benefit from this association. If one provides the right growing media in which the plants thrive, it is likely that one has also provided optimal conditions for the fungus to grow. We think therefore that it is quite likely that mycorrhizae will be found on cultivated orchids once their roots are properly examined.

The bulk of the book consists of a catalog of hardy orchids. The utility of this clearly written and well-illustrated section is substantial because it provides detailed information on individual species and on cultivation methods applicable to larger species groups. An impressive total of 104 different species are listed for which detailed growing conditions are provided, such as the most optimal fertilization times and U.S. Department of Agriculture winter hardiness zones. Nevertheless, with regard to the latter point a more extensive discussion of summer temperature limitations would have been handy because, for example, hardiness zone 8 is definitely not the same in Georgia versus Washington State. A bit more emphasis could also have been given on the importance of using material of local populations when growing widespread species because these are more successfully adaptable to local conditions than plants from distant parts of the range, where the climate differs considerably. The discussion of growing conditions of species such as dragon's mouth orchid (Arethusa bulbosa), lily-leaved twayblade (Liparis liliifolia), and the tubercled orchid (Platanthera flava) that are not yet available for culture are of value for development of future propagation for horticultural or conservation purposes. Claims that several orchids require bog conditions in cultivation, however, seem a bit too strict. Species such as the North American yellow lady's slipper (Cypripedium pubescens), the showy lady's slipper (C. reginae), and the heath spotted orchid (Dactylorhiza maculata) are perfectly happy in mesic garden conditions despite generally preferring wetland conditions in the wild. They are even easier to grow than the book already suggests. The lack of information on the risk of introgression of genetic material of introduced plants from different geographical origins into wild populations is an unfortunate deficiency. Because the author lists multiple species of lady's slippers (Cypripedium), snake-mouth orchids (Pogonia), and lady's tresses (Spiranthes) that are likely to produce viable offspring with their congeners, we think more information could have been provided about the potential risks of unplanned hybridizations.

The largest weaknesses of this book are several distracting factual errors. For example, it is claimed that the ivory lady's slipper (Cypripedium kentuckiense) is federally endangered, whereas it is listed as endangered only in Tennessee. The giant helleborine (Epipactis gigantea) is depicted as a European native introduced to the Pacific Northwest and assumed to be essentially similar to the broad-leaved helleborine (E. helleborine), whereas it is native and widespread in western North America. It is unmistakably morphologically distinct from the latter species (Luer 1975). The author also states that orchid leaves lack stomatal guard cells and that the majority of orchid species are terrestrial. A considerable body of literature on these subjects, however, demonstrates that orchid leaves do have guard cells and that over 70% of all species are epiphytes (Dressler 1993). These errors left the impression that relevant scientific literature was not always consulted.

The author concludes the book with a chapter on the value of conservation methods for popular species collected from the wild, often illegally or very destructively, and uses the tropical aquarium pet trade as an example. It is hard to underestimate the value of learning how to raise and reproduce a wide variety of imperiled species in captivity, plants or animals, which is only just beginning and not yet widely accepted. Ex situ propagation methods have broad application across much of Earth's biodiversity and can work to the benefit of those who enjoy species in the wild. The challenge is to convince a wider audience that ex situ propagation is useful and not wrong. The shortcomings of this book aside, we recommend it to anyone interested in growing hardy orchids because in our view horticulturalists and conservationists will find it of use. It brings together a great deal of previously scattered information for a large audience reaching far beyond the hobbyist gardener. The main message is not only that it is possible to grow hardy orchids but also that it is not intrinsically wrong. Instead, growing orchids can help imperiled species survive by providing a stock for reintroductions. We are confident that this book will therefore contribute substantially to preserving hardy orchids threatened in the wild, although the author rightly emphasizes that no garden can substitute an unmolested habitat.

Ancillary