FIVE FAVOURITE COOL-GROWING SPECIES by Rex Johnson
There are over a thousand species in the genus Pleurothallis, which originates in Central America in a variety of habitats and temperature regimes. Many require a minimum temperature of 12-15˚C in winter but two species that I grow, namely Pleurothallis grobyi and P. tuerckheimii, manage with a winter minimum temperature averaging 8-10˚C, although it occasionally falls as low as 5-6˚C.
Pleurothallis grobyi is a small, tufted plant that I grow mounted on a tree fern slab. In nature it is found as an epiphyte at altitudes from sea level to 2000 m, so it is quite adaptable to a range of temperatures. The small, straw-colored flowers, measuring 5 mm across by 12 mm tall, are well spaced on a 70-80 mm raceme. Each raceme carries up to a dozen flowers, although the first ones to open begin to fall before the last buds have opened; flowering lasts for several weeks.
Pleurothallis tuerckheimii grows next to P. grobyi in my glasshouse but under very different conditions, being planted in an 80 mm pot filled with fresh Sphagnum moss. During its growing season (spring and summer), it is given plenty of water but little fertiliser. In autumn last year it produced 96 inflorescences, each carrying an average of 22 flowers, and this year it has flowered just as prolifically. The flowers are very dark, almost black but even when fully open they fail to impress most orchid growers! Very weak liquid fertiliser is applied only occasionally.
The Central American genus Scaphosepalum is closely related to Pleurothallis and Masdevallia, and contains about 30 species. I grow two species, Scaphosepalum swertiifolium and S. gibberosum, both planted in pots containing Sphagnum moss. Fresh moss is a good potting medium for many epiphytic orchids, although some growers have difficulty in keeping the moss nicely damp without being too wet. Dry moss can hold up to ten times its weight of water and become too soggy for good culture. If the moss becomes completely dry, it can be difficult to re-wet unless submerged and soaked in water. Both my scaphosepalums grow very well when I keep the moss nicely moist.
Both of the above species are sequential flowerers, producing one flower after another at the top of the wiry inflorescence over a period of many months, more than a year in the case of my plant of Scaphosepalum swertiifolium. They grow in the same glasshouse as my other pleurothallids, usually at a minimum temperature of 8-10˚C during winter. Scaphosepalum gibberosum has an odd-looking bloom, which I call my “water buffalo flower” because its petals reflex like the horns of a water buffalo. The flowering stem zig-zags from flower to flower. As soon as the latest flower is fully open, the previous one withers and falls.
Masdevallia huebschiana is a multi-flowering masdevallia bearing 2-5 flowers, each 10 mm across, on an inflorescence measuring 80-100 mm tall. It is not commonly seen in Tasmania and is sometimes confused with M. polysticta. Masdevallias grow well in Tasmania because of our cool climate. It is easier to maintain a warm house in a cool climate than it is to maintain a cool house in a warm climate. Many growers use Sphagnum moss as the potting medium for masdevallias but I use mulched leaf litter from beneath Myrtle trees. This partly decomposed material has a coarse structure and is both free draining and water-retentive. It also provides the plant with nutrients, so little liquid fertilizer is needed. A division of my plant has also been fastened to a mount of carpet under-felt and bush moss fixed to a piece of old fence paling, where it grows and flowers well.