Dendrobium anosmum

Dendrobium anosmum -
Every One Should Have One
By Dr. Yin-Tung Wang

Reprinted from the October 1999 issue of Orchids -- The magazine of the American Orchid Society

Dendrobium anosmum

I was conducting my regular weekly orchid tour in my orchid research greenhouse one Thursday afternoon, when I overheard a man telling another: "John, this orchid flower has an odor". An older gentleman stared at the man for a moment and corrected him. "You see, my friend, men and pigs have odors. The ladies and flowers have fragrances". Boy, I knew he was right just from my personal experience.

I love fragrant orchids. If you share this passion with me, there are plenty of orchid species and hybrids for you to collect. Some orchids have pleasant fragrances. The popular Oncidium Sharry Baby 'Sweet Fragrance' has flowers that may lure chocolate lovers to them. Flowers of Maxilaria tanuifolia smell like coconut oil. The bright yellow Lycaste aromatica flowers have a strong cinnamon scent. Many Cattleya Alliance plants have fragrant flowers. When my Blc. Ronald Hausermann 'Betty Jo' put out 25 flowers at once last fall, I could smell its wonderful fragrance more than 60 feet downwind. The scent of other orchid flowers (such as some Bulbophyllum species), however, may keep people from entering a greenhouse. The excellent book "Scent of Orchids" by Roman Kaiser tells us the composition of fragrances of various orchids. Many fragrant orchid flowers smell much better during the morning hours under bright light. The fragrance fads off after noon. Others, such as the Brassovala species and many of their hybrids, do not emit fragrance until it has experienced complete darkness. However, one may fool them to emit fragrance by placing them in a dark place for 20 to 30 minutes. In general, good lighting is essential for sustained fragrance over an extended period of time.

One of the orchids species with a powerful fragrance is Dendrobium anosmum (syn. Dendrobium superbum). "Anosmum" means without scent in Latin. This species is native to New Guinea, the Phillippines and north to Sri Lanka and Thailand. The long slender pseudobulbs are said to grow to 3 meters (nearly 10 feet) in length. However, in cultivation, especially when it is mounted, the pseudobulbs often do not even reach three feet. When well grown in a pot, the pseudobulbs can easily reach five to six feet. This species has lavender flowers that have two burgundy spots on either side of the lip towards the inner base. An albino form with pure white flowers are available. The flowers of some forms reach only half-open, while others open fully. Although the literature says that each node produces 1-3 flowers, my specimen-size plants produced four flowers on many nodes. Although I enjoy it, the fragrance of these flowers can be overpowering to some people. It smells like raspberry, strawberry, rhubarb, or hyacinth, depending upon one's imagination. Even the dried up flowers keep the fragrance for a while. Flowers of Dendrobium parishii has a similar fragrance, but it has much shorter and stockier pseudobulbs. Roman Kaiser in his book "The Scent of Orchids" describes that 2-penta-decanone is responsible for 50% of the fragrance that is accompanied by a serious of odd-numbered 2-alkanones and some of their 2-alkyl acetate derivatives. Both the lavender and white flowers have identical fragrance.

In the warm south Texas, flowers of Dendrobium anosmum reach full bloom in late March and remain in bloom for about four weeks. Under cooler conditions, the flowers may last longer. A well grown pseudobulb can produce over 100 flowers.

After flowering is over, the unbloomed nodes near the tip of the pseudobulbs and a few nodes just below the lowest flowers will start to produce keikis. A keiki may be removed from its parent plant when a good root system has developed in a couple of months. These plants normally do not produce flowers during the first year in existence, but will bloom during the next season. I pot these keikis one to a four-inch pot in late spring or early summer. These plants remain in such small pots until plants have ceased growing in December the following year. The medium consists of equal parts of medium grade orchid bark, hardwood charcoal, sponge rock, and chunky peat (all from Stewart Orchids). I use this same medium for catasetums, cattleyas, cymbidiums, dendrobiums, oncidiums, phalaenopsis and just about all orchids species and hybrids that I grow.

The new growth starts at the base of a one-year-old pseudobulb when flower buds start to swell. That is in late February in deep south Texas. There may be as many as four to five new growths from the base of a three-year-old plant and one to three from a two-year-old plant. When the pseudobulbs of the current season are in active growth, plants need a liberal supply of water and nutrients. I apply Peters 20-20-20 in the amount of about one teaspoon per gallon of water at each and every watering. I leave the young plants on the bench and allow the pseudobulbs stay on the bench until they cease growing in early December. These first-year's growth are usually no longer than one and one-half feet and do not flower. The next year's growths usually reach four feet long. At the end of this growing season, I move them up to one gallon pots and use bamboo sticks to stake up the stems straight up. However, many people grow this species in baskets.

When measured at noon in the summer, my Dendrobium anosmum plants receive 4500 foot-candles of light. They receive 3800 foot-candles in the winter. However, lower light intensities close to 3000 foot-candles during the entire year may be adequate for good flowering. Maximum air temperature in the summer reaches 95 °F in the summer. My three-year-old plants produced pseudobulbs over six feet in length.

This species, like Dendrobium nobile, must be exposed to moderately low temperatures to induce flowering. In the natural habitats, Dendrobium anosmum may be exposed to temperatures as low as 50 °F, but, in cultivation, 60 °F is adequate to trigger flowering. When growth has ceased, I move plants either to another much cooler greenhouse or to outside. After three to five weeks of lower temperature treatment, the upper two-thirds of the leaves start to turn yellow and fall off. The lower leaves may stay green if the temperature during this period is not too low and/or roots do not become very dry. High light is said to be necessary during this period for maximum flowering. Reduce watering to just enough to keep plants from shriveling. However, in south Texas, I do water them as soon as the medium becomes dry even in the winter. Fertilization can be reduced to quarter strength or stopped completely. As a precaution, do not leave plants outside if the temperature is predicted to fall below 50 °F (10 °C) for long. Watering must be increased when the buds on the nodes start to swell for best flowering .

Unless keikis are being produced, I cut off the upper portion of the pseudobulbs after the blooms have fallen off. If an old pseudobulb has some green leaves remaining on its lower portion, do not remove them because these leaves provide foods to the new developing pseudobulbs for fast and better growth to ensure good flowering the next season.

Dr. Yin-Tung Wang is a professor of floriculture with the Texas A&M University System. Among others, Dr. Wang conducts research on orchid production and physiology. He offers free public tours of his orchid research greenhouses on Thursdays at 4:30 P.M. He last wrote about regulating the blooming time of the phalaenopsis orchids in the September 1997 issue of ORCHIDS. He is a member of the AOS Research Committee and a member of the Houston and the Rio Grande Valley societies, as well as an honorary member of the South Texas Orchid Society. Address: 2415 East Highway 83, Weslaco, TX 78596. E-mail: yt-wang@tamu.edu .