This was the first of our special presentations is by that world renowned Disa hybridizer and all round great guy, Wally Orchard.  He learned about Disas at his father's knee in South Africa.  He has the largest Disa nursery in the Pacific Northwest and few know more about Disas.  There were to be a number of pictures included with this topic but he has put them all on his web page so you can see them there.

DISAS                 by Wally Orchard

Disas are terrestrial orchids, occurring mostly in southern and tropical Africa. Of the over 200 known Disa species, only a handful (described below) are commonly cultivated. These all grow in mountainous areas close to Cape Town, on the southwestern tip of the African continent. There they are found in association with perennial water on the banks of streams, on waterfalls and on damp cliff faces. These mountains are composed of sandstone and the water, although quite acidic, contains very low concentrations of minerals. The winters are mild and wet, and even in the hot summer months the roots of the plants are cooled by the presence of water.

Mature Disas develop large, fleshy underground tubers. The plants are deciduous, and after flowering (sometimes even without flowering) the plant dies; with luck, a new tuber and a growing shoot develop. Small plantlets (keikis) may spring up close to the stem of a mature plant, and underground stems (stolons) can lead to plantlets at a distance from the main plant. Disas grow strongly from spring through fall, and flower, depending on species, throughout the summer months. During winter they show little growth above ground, though there is always some root growth activity.

Disas were successfully cultivated and hybridized at Kew Gardens, London, toward the end of the nineteenth century, but then faded into obscurity for many years. More recently, various South African growers took up the challenge and have made great strides in bringing new species into cultivation, improving cultivation methods and making many new and beautiful hybrids. Excellent plant material is now available from several of these enthusiasts, as well as various sources in the United States.

Disa species of interest

Disa uniflora is the best known species, and for good reason. The magnificent flowers can spread over 4 inches (10 cm) across and cultivated plants produce several flowers on a spike. The hood (dorsal sepal) has pronounced veins of darker color. The wide range of colors includes pink, orange, red, yellow and other similar shades. The stem length and the size, shape and number of blooms are also very variable. Most of the Disa hybrids of interest contain at least 50% of this species in their genes.

D. racemosa grows in marshy areas and flowers best after fires. The mauve flowers, smaller than those of D. uniflora, are shapely and well-spaced on stems up to 3 ft (1 m) long. Although this species does not bloom readily in cultivation, some of the most sought-after hybrids (e.g. D. Foam) are derived from it.

D. tripetaloides grows in dense colonies on stream banks, producing numerous small but shapely white to mauve flowers, with a distinctive pink stippling in the hood, in contrast with the veins seen in D. uniflora. The spots in the dorsal sepal are often passed on to its offspring, such as the well-known hybrids, D. Kewensis and D. Watsonii.

D. aurata is similar in form to the previous species, but the flowers are an intense yellow, with orange stippling in the hood. D. cardinalis has slightly larger, scarlet flowers, and has led to magnificent red hybrids including D. Kirstenbosch Pride and D. Helmut Meyer. D. venosa, D. caulescens and D. atricapilla, while less known, have also been flowered in cultivation and used for hybridization.

Cultivation

Disas need to be kept constantly moist, and for this reason it is important to use a growing medium which does not break down too easily. The medium should also display instantaneous drainage and should allow good aeration of the roots. Most South African growers use coarse (1-2 mm or 1/16th inch) silica sand or river sand, often mixed with a small amount of fern fiber to promote acidity. This is an ideal medium if you can get it to work - it is cheap, reusable, and makes repotting quick and easy. Unfortunately I have had no success with it! Disas do very well in New Zealand sphagnum moss, which is the medium of choice with some US growers. But this medium gets entangled in the fragile Disa roots, and also begins to decompose rather quickly. I am working with mixes of volcanic pumice, vermiculite, coarse peat moss, redwood wool and a small amount of charcoal. It is a good idea to experiment to find a medium which works well under your particular growing conditions.

Disa plants tend to be quite small, and pots of about 3 to 4 inches (7-10cm) square and similar depth are ideal. Some growers have been very successful using net pots of up to 6 inches in diameter; these pots aid aeration and encourage stoloniferous growths. Water quality is probably the single most important factor in Disa culture. The water should be soft - that is, it should have a low concentration of dissolved mineral salts. Rainwater, collected from the roof during a good downpour, is ideal. Some growers, including several in California, get excellent results using tap water. Disa roots must be kept damp at all times, and the medium should never be allowed to dry out. Most growers water from above on a regular basis, typically 3 times a week in summer, 1 to 4 times a month in winter. In addition to the regular watering, an occasional extra heavy soaking will help in the key process of leaching accumulated mineral salts from the medium. With fertilizer, the key is to use very dilute concentrations (one tenth to one quarter strength) of a balanced to high nitrogen formulation containing all trace elements (e.g. 20:20:20 or 30:10:10) on a regular basis during the growing season, and less or none in the winter months.

Disas like relatively cool temperatures, especially in their root zones, and do best with humidity in the range 50-70%. In winter, while they will survive sub-zero temperatures, they should not be subjected to a hard freeze which will probably kill them. In the Pacific Northwest, a cool greenhouse would be ideal. Not possessing such a luxury, I grow mine outdoors under shade netting from April to the end of October; in winter they are put on carts and spend nights in an unheated garage, days out in the open. Beware of bringing Disas into a centrally heated house, as they cannot tolerate warm temperatures combined with low humidity! They like bright light and blue sky, but generally need to be under some shade cloth in summer to avoid desiccation.

Disas are prone to fungal rot, in which the whole plant and root system decomposes into a soggy pulp. Occasional or even regular application of fungicide is advisable. Watering should be severely curtailed in winter in order to minimize the danger of bacterial and fungal infections. In my experience, the main insect pests affecting Disas are aphids and earwigs and thrips. In treating Disas with either insecticides or fungicides, it is safest to use wettable powder formulations and to try the treatment on a small sample of plants before you apply it to your entire collection! Disas need regular repotting, which is best done in the fall, after the flowering stem has died back.

Disas are not the easiest of orchids to cultivate, but, with experience and care, the results can be spectacular. If you are thinking of putting a couple of them in amongst your other orchids, to see how they do, you are probably going to be disappointed by the results. But if you are prepared to give them the specific attention and treatment that they need, you might be well on the way to becoming the latest victim of Disamania!

    Wally is the owner of Afrodisa Orchids.  His new web site is <http://corchard.home.attbi.com/>