Clinging to rocks and trees, the Australian Dendrobiums flourish along the eastern slopes of Australia. Within that 1,500 mile long area, the habitat ranges from rocky outcroppings to subtropical rainforests. While there are approximately 56 native Dendrobiums in Australia, naturally occurring hybrids and orchid enthusiasts have produced thousands of named and unnamed varieties. At Flowers by the Sea, we grow the lithophyte Dendrobiums, which grow along the rocky canyon walls.
Dendrobiums require bright filtered light, between 3,000 and 4,000 foot candles. A brightly lit south, west or east facing window with sheer curtains generally allows sufficient light for the orchid to thrive and bloom. A grow light provides additional light when there isn't enough natural light. When growing Dendrobiums outdoors, or taking them outside for their summer vacation, place the orchids in the dappled shade of the trees. If the leaves are dark green, the orchid needs more light, but use caution as too much sun can burn the leaves.
In their native habitat, the Dendrobiums thrive in temperatures ranging from 32 to 90 degrees F. At Flowers by the Sea, we grow our Dendrobiums in a high-light shade house that ranges from 30 degrees F in winter to 85 degrees F in summer. Temperatures drop at night to the high 50s, providing the temperature variations between day and night that promote blooming. In general, Australian Dendrobiums can be grown in shady locations outdoors in U.S. Department of Agriculture plant hardiness zones 9 and above when provided with sufficient humidity and protected from frost.
Along the eastern coast of Australia it rains eight to 10 times a month, providing regular water to the native orchids. The plants store water in thick, fleshy stalks called pseudobulbs. At home, water indoor Dendrobiums once a week when the potting mix is dry. Place the flowerpot in the sink and add water until it drains from the bottom of the pot. Wait until the water has completely drained and then repeat watering twice more to ensure that the medium is completely moist. Avoid using softened water; it contains too much salt. Outdoors, the Dendrobiums may require twice weekly watering in summer, depending on the temperature and humidity level. In late fall and early winter, rest the plants for 30 to 60 days by only misting the roots and foliage. Continue to maintain a high humidity around the orchid. When new flower spikes appear, resume watering.
After watering, fertilize the Dendrobium with a dilute fertilizer solution. The American Orchid Society recommends using a 20-20-20 liquid fertilizer at one quarter strength, or 1/4 teaspoon per gallon of water. Add the solution to the flowerpot until it drains from the bottom of the pot. Avoid fertilizers formulated with urea. At FBTS, we use a solution of 200 ppm, or 5 tablespoons to 1 gallon of water, of Maxicrop kelp and urea-free fish emulsion. We also use compost tea to nourish the orchids.
Because the Dendrobiums are subtropical orchids, they need a humidity of 60% or more. Outdoors, soaking the ground underneath the orchid and using misters during warm weather raises the humidity around the plant. Indoors, place the flowerpot on a tray filled with pebbles and water, group similar plants together, and add a cool steam vaporizer to raise the humidity in the air. The additional moisture in the air also helps offset cooler temperatures in winter and summer heat.
The lithophytes Australian Dendrobiums grow naturally amid the rocks on canyon walls. At Flowers by the Sea, we use rock mediums mixed with tree fern, osmunda fiber or coir chunks to replicate the natural habitat. While bark medium can be used, it breaks down rapidly. When planted in a rock medium, the Dendrobiums need repotting every three to four years.
When the roots and plant are "climbing" out of the flowerpot, it is time to repot. Generally, Dendrobiums are repotted at the end of the blooming period. Prepare the new medium by soaking it for several hours to ensure that it is consistently moist throughout. Carefully remove the Dendrobium from the pot. Examine the roots and trim any decayed or dead roots, sterilizing the pruners between each cut with a solution of equal parts water and rubbing alcohol. After adding a layer of the fresh medium in a new, slightly larger clay flowerpot, nestle the roots on top of the medium, and add more medium to fill the flowerpot. Tamp firmly around the roots to secure the orchid. Here at FBTS, we place the flowerpot on a plant heating mat set at 80 degrees F until new roots emerge and are at least 1 inch long.
Keikis are the baby plantlets that emerge from the canes on parent plant. Wait until the roots on a keiki are 1/2 to 1 inch long. Then remove the keiki by cutting just above and below the keiki with sterile anvil pruners. Dab a little fungicide, such as thiomyl or ground cinnamon, onto the cut ends of the parent cane and the keiki. Plant the keiki in a rocky medium in a small clay flowerpot.
Flowers by the Sea brings a variety of Australian Dendrobiums to the orchid enthusiast. These are among the easiest orchids to grow. Mature plants can put out numerous new spikes and may have thousands of flowers in bloom at one time in a spectacular, sweet-smelling display.