Native to Southeast Asia, the genus Dendrobium is one of the largest of all orchid groups. There are about 1,200 individual species, and they grow in all manner of climates, from hot, wet lowlands to high-altitude, colder mountains. Growers usually divide dendrobiums into groups based on their growing conditions. All dendrobiums are epiphytes, meaning that they grow on other plants. In nature, they grow on the branches of trees. Some are deciduous and some hold onto their leaves all year round.
Serious collectors often favor the D. nobile, but the most common kind of dendrobium—the kind gracing grocery store shelves—is a hybrid Dendrobium phalaenopsis, also known as a dendrobium orchid.
How to Grow Dendrobium Orchids
While they are considered a great orchid for beginners, some people have trouble with Dendrobium phalaenopsis hybrids. With the hybrids, think more of everything—more light, more water, and more fertilizer.
The plants are robust growers that send up at least one new upright cane every year from creeping rhizomes. Don't cut off old canes, as they store nutrients and water to keep the plant healthy. Older canes will sometimes flower or produce tiny plantlets, called keikis, that can be potted up on their own after they develop roots.
You can find a wide range in the color, size, and shape of the blooms. The long-lasting sprays of flowers remain in bloom for six to eight weeks. You can use the sprays to use as cut flowers for arrangements. These bloom several times throughout the year, depending on conditions. To help provoke a flower spike, slightly drop the water and nighttime temperature.
These plants like strong, natural sunlight. They will grow in lower-light conditions, but it is unlikely the plant will bloom well. The appearance of keikis often means the plant isn't getting enough light. On the other hand, if you see yellow leaves you may have given the plant too much direct sunlight.
Orchids don't grow in soil, but rather in a special mixture that mimics their environment in the wild. Purchase a commercial orchid potting medium, which contains peat moss, perlite or fir bark, or make your own that has these ingredients in it. Make sure that the "soil" has aeration and is well-draining, so the roots aren't left in moisture for a lengthy period of time.
During the growing season, dendrobiums like high humidity and lots of water. As with all orchids, the frequency of watering depends on your growing conditions, but at least weekly is a good idea during the summer. Don't leave them in a tray of water as that can rot the roots. After the growing season, cut water back somewhat (maybe every 10 days), but do not suspend watering.
Feed heavily during the growing season with a weak fertilizer solution containing lots of nitrogen, or use a balanced fertilizer like Peters 20-20-20 at quarter-strength with every watering. At the end of the growing season, reduce fertilizer by about half to help provoke a better bloom.
Temperature and Humidity
There are considered warm-house plants by growers, meaning they favor conditions in a warm greenhouse. The temperature for these plants should be above 60 degrees Fahrenheit at all times. Although experience has shown they can withstand a few nights down to 50 degrees Fahrenheit, this should be avoided if possible. A slight drop in nighttime temperature will often stimulate a bloom.
These orchids like a humidity level of 50 to 70 percent. Brown leaf tips are a sign that the air is too dry for your orchid, and you may need a humidifier.
Potting and Repotting
These are naturally epiphytic orchids that will thrive in hanging baskets with little or no potting media (in superb conditions), or they will do well in fast-draining media as a windowsill plant. In fact, they do best in a smaller pot with only an extra inch beyond the root ball. If you have a larger planter you want to use, you can disguise it with a smaller pot inside the decorative one.
Dendrobiums don't like potting soil but want an orchid mix or a soilless potting medium. A mixture of clay aggregate, perlite, and coconut fiber works well. These plants are shipped from Hawaii, Taiwan, and throughout Asia, and some growers have started selling them grown in wood chunks. This is not a favorite potting situation because the plants are often top heavy and the wood gradually rots away.
Repot at the beginning of the growing season when necessary, usually every couple of years at most. If your plant has more than three leafless canes, you can remove the oldest when you are repotting it.
Propagating Dendrobium Orchids
If your plant has at least four canes that are bearing healthy leaves, you can divide it. Use a large stiff knife to cut through the rhizome and root mass, attempting to keep the root mass intact as much as possible. Remove all the growing medium from the root mass, and then cut away any long, dangling or dead roots.
Put the plant in a pot in the appropriate size—it shouldn't be too larger. Add orchid potting mix around the roots, so the junction of the plant and the root is a half-inch below the mixture. Pack the potting medium firmly, and wait one week to water it thoroughly.
After the bloom is done, you can cut off the spike above the leafy part of the stem. However, you should not remove any old leafless canes.
Dendrobium orchids are prone to root rot when they're overwatered or left to sit in water. Potential symptoms include wilting and shriveling, yellowing leaves. If the roots appear dark brown or black, trim off the infected parts of the root, disinfecting the pruning shears between each cut. Repot the plant in fresh orchid mix that's been drenched with a fungicide.
Additionally, your plant could become infected with brown spots, which can be fungi or bacteria. Leaf spots are often caused by high humidity or too little area movement. Remove the heavily damaged leaves and trim off the affected areas, sterilizing the tool between cuts. Spray the orchid with a combination fungicide and bactericide, but avoid copper fungicide.