(Editor's Note: This article was originally published on September 5, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
I think most gardeners would agree that orchids are considered the most exotic and beautiful of all flowering plants. There has been a certain allure surrounding orchids ever since gardeners began to cultivate them. The vast majority of the world's orchids are tropical species which require indoor culture. However, there are a few very showy, hardy orchids which can be cultivated outside in our gardens. The most obvious are the lady's-slippers from the genus Cypripedium. However, less well known are the Calanthe orchids and some are surprisingly hardy.
The genus Calanthe gets its names from the Greek kalos, beautiful and anthos, flower. There are about 120 species worldwide, hailing from temperate to tropical regions of Asia, Polynesia and Madagascar. This article will discuss those few that originate from the temperate zones of eastern Asia. There are only 5 species of note, all considered hardy to zone 6b. In the wild, the hardy Calanthe grow in dappled, deciduous woodlands. In the garden, you should try to simulate similar growing conditions. Mix plenty of rotted leaves, peat and sand into the existing topsoil to create an open, gritty mix that retains some moisture. The growing area should be well drained in winter as too wet soil will cause them to rot. They make admirable companions for Trillium, Asarum, ferns and Hosta. If grown well, they can form quite large clumps over time.
In late spring, plants will send up pairs of leathery, pleated leaves. These leaves will reach 20 to 30 cm in length. Flower stems arise at about the same time and may reach upwards to 30 to 45 cm with a spike of 10 to 25 flowers come June and July. After blooming, dead-head to prevent seed production as this can reduce future blooming. In milder areas the leaves will remain evergreen but at the edge of their range, the foliage may look a bit tattered come spring. However, resist the urge to cut off the old foliage as this may cause the spread of virus. These old leaves will die away naturally as the new leaves emerge.
Calanthe reflexa and C. aristulifera are two closely related species that bloom in August
As mentioned, there are only five Calanthe considered hardy to zone 7 (maybe 6 if well mulched). They do well in the Pacific Northwest, Southeastern U.S. and milder areas of Europe. In North America, I have seen them growing as far north as the Detroit area. Alas they are not hardy in my region but northern gardeners don't despair! They may be grown indoors. I have several that are overwintered in a cool basement window (5 C minimum). I grow them as pot plants outside in summer, placing the pots in dappled shade. They remain outside until early November then are brought back into the cool basement again. I grow them in a mix of peat, perlite, rotted leaves, sand and fine bark (the same mix I use for terrestrial tropical orchids like Paphiopedilum and Cymbidium).
Among the most readily available Calanthe are C. sieboldii var. striata and C. discolor
Calanthe sieboldii var. striata is among the most common and robust. This species has brilliant yellow flowers which are among the largest of the hardy Calanthe. The hardiest species is C. discolor. This species has been known to survive in zone 5b when heavily mulched. The flowers are two-tone purple-brown with a white lip. Calanthe tricarinata has quite striking flowers whose petals and sepals are bright green with a contrasting red, heavily frilled lip. Calanthe reflexa is a late bloomer (August) whose flowers are white with a contrasting lavender lip. It is not quite as hardy as the other species mentioned. The rarest hardy Calanthe in cultivation is C. aristulifera, a close relative of C. reflexa. It also blooms in August but has pink flowers. Calanthe bicolor is often considered a species, but in fact, is a natural hybrid between C. discolor and C. sieboldii. Flowers are variable in colour but are mostly autumn tones of bronze, orange and yellow. Most recently there have been a series of Calanthe hybrids developed among the above mentioned species . These are called the Hizen, Kozu and Takane hybrids and are available in a rainbow of colours.
Above are shown C. tricarinata in situ and an example of one of the Kozu hybrids
If orchids are your thing and you are fortunate to live in a mild hardiness zone, then Calanthe orchids are a very satisfying and exotic addition to your garden.
I would like to thnak the following people for the use of their pictures: K. Keiko (C. reflexa), T. Rodd (C. tricarinata) and Lophophora (C. sieboldii var. striata and C. discolor)