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Dendrobium Culture: Phalaenopsis and Semi-Antelope types

Photo copyright William Curtis

Den. Classic White 'Memoria Yukie
Nakano', AM/AOS

Dendrobium is the second largest genus in the Orchidaceae; the largest is Bulbophyllum, with possibly more than 2,000 species. Dendrobium is so massive that its more than 1,000 species are divided into several sections and subsections based on both floral and vegetative characteristics. Hybrids made within section Phalaenanthe are commonly referred to as phalaenopsis-tyjpe dendrobium hybrids or, more comnonly, den-phals due to their resemblance to flowers of the genus Phalaenopsis (moth orchids). Hybrids within the section Spatulata are commonly called Antelope-types because their twisted petals resemble the horns of some antelope and hybrids made between the two species are referred to as semi-antelope types. Among the easiest of orchids to grow under most conditions, den-phals and semi-antelope types are evergreen orchids that reward the beginner with sprays of vividly colored long-lasting flowers in exchange for minimal care.

Arched inflorescences are borne on upright, cylindrical, 2- to 4- (or more) foot- tall pseudobulbs (sometimes called canes), which are slightly swollen at or above the middle. New growths develop from growing points (called "eyes") near the base of the pseudobulbs and sometimes higher near the leaf joints. Somewhat leathery, 3- to 6-inch-long leaves clothe the upper half of the pseudobulbs and usually remain for one to two years.

The number of flowers borne on an inflorescence increases as the plant ages. First-bloom seedlings often bear one to five flowers per spray; mature plants can produce 20 or more flowers per inflorescence on each of many inflorescences. Individual flowers last six to eight weeks and provide color for several months during the warmer parts of the year. Den-phal flowers are typically round and flat with overlapping sepals and petals. They range from pure white, or green to deep plum and shades and hues in between. Flowers of semi-antelope types have narrower petals that are more or less twisted depending on the extent of antelope-type species in their background. Many of these hybrids have dramatically colored flowers with starkly contrasting lips.

Photo copyright Greg Allikas, Orchidworks.com

Den. Thai Pixie 'Orchid Acres', AM/AOS

Culture

Temperature and Humidity Den-phals and semi-antelope types thrive under many temperature and light combinations. The recommended temperature range is 50 to 90 F, but temperatures a few degrees higher or lower are acceptable and usually cause no detrimental effects. A relative humidity of 50 to 60 percent is optimal. In climates with lower humidity, mist the plants on hot, dry days. Avoid excessive water on the leaves and in the crown of the plant during humid and cool weather to prevent crown rot and fungal problems. Fans that move the air without causing excessive chilling or drying keep the foliage dry and also help remove heat from the leaves during hot weather.

Light Direct filtered sun is essential for flowering, but provide 30- to 70-percent shade during midday. Bright light will generally encourage flowering, provided excessively high leaf temperatures are avoided. Although these dens can be grown under artificial lighting, this practice is not recommended due to the plants' height.

Watering The moisture needs of these orchids are similar to those of cattleyas. Thoroughly soak the potting medium, then allow it to dry before watering again. Watering twice a week is generally adequate with properly potted plants in most climates. In winter, watering frequency may be reduced if the plants take longer to dry.

Nutrition Apply a balanced fertilizer containing minor elements regularly. When using inorganic media it is especially important to provide an adequate mix of nutrients, including minor nutrients. This is important because little nutrition is provided by the decomposing medium. Avoid prolonged use of high-nitrogen fertilizers (such as 30-10-10), because they encourage the growth of algae and pathogens and promote excessive leaf growth rather than the development of roots and flowers. Feed with every watering at half the recommended dilution rate. This will guarantee adequate nutrition while avoiding any chance of root-tip damage from excessive nitrogen.

Potting Many dendrobiums, and these hybrids in particular, grow and flower bet-ter when left undisturbed in relatively small containers. Choose a potting material that will not decompose quickly. Mixtures of fir bark and inorganic material (lava rock) have yielded positive results. The inor-ganic materials impart a porosity to the mix that permits air circulation around the roots. This mixture allows as much as three years to lapse between repotting. It is important, though, to avoid overpotting, because this slows growth and reduces flowering significantly.

Photo copyright AOS

Den. Lim Chong Min
'Spring Orchids', JC/AOS

These dendrobiums are suited to hanging in the greenhouse and west- or south-facing windows in the home. Clay pots with slits or extra holes are preferred in humid environments, while plastic pots with extra holes are adequate for drier climates. When repotting, avoid planting the growths too deeply in the mix because the eyes, from which new growths emerge, will rot easily if covered with mix.

Problems Spider mites may be a problem in early summer. They can be found on the undersides of leaves and can be quite destructive if not eliminated. Watch for snails that can quickly eat the dormant eyes from around the base of the pseudobulbs.

When kept in a container too long, or another misfortune is experienced, these dendrobiums tend to develop keikis (plantlets) from dormant eyes located near the top of the plant. Once the keikis have grown leaves and developed 1-inch-long roots, remove them and pot separately. They will grow into duplicates of the original plant. Development of keikis on a Dendrobium is generally an indication that there is a problem with the parent plant which will often die soon after the keikis have developed.

The article above has been adapted from an article written by Bob Davidson and originally published in the American Orchid Society Bulletin in October 1993.