Dendrobium nobileDendrobiums come in many varieties, but in this website and cultural guide, reference is made only to the nobile types. Nobile are natives of the Far East in countries such as Burma, India, Thailand, and Vietnam. They grow in their natural habitat on branches of trees in the forest from lowlands to quite cool highlands of 4000 feet elevation in the Himalaya mountains. They are extremely hardy surviving warm, how, and down to freezing temperatures. If kept dry, they survive winter temperatures of 37º to 39ºF (3-4ºC) and flower around April. If temperatures are maintained at about 62º to 64ºF (17-18ºC) as soon as buds appear, they will flower in January or February.
FloweringPoor flowering in spite of robust growth and appearance of offshoots (keikis) are the most common problems with nobile type dendrobium. These can be solved by following these precautions:
Potting media, containers, and repottingTree fern fiber, osmunda, fir bark, sphagnum moss and other media appropriate for cattleyas may be used for nobile type dendrobiums. A mixture of perlite (1-2 parts), and peat moss (1 part) with pH controller can also be used. A slightly acide medium (pH 5) which drains well but still retains some moisture is ideal.
Clay pots are recommended for sphagnum moss or media which retain moisture. For other media which drain well, plastic or polyethylene pots are recommended.
Appropriate post sizes are as follows: For a small plant up to 3 inches tall, a 2.5" pot is good. for a plant 5 inches tall, a 3" pot is adequate; and for a plant 10" tall, a 4 inch pot is fine. Overpotting is not good for growth of small plants.
WateringThere is a direct relationship between temperature, light, and watering. When temperatures begins to rise in the spring, gradually start watering. In the summer when temperature is high and sunlight is strong, water almost every day to keep plant from drying. From about late September as the temperature begins to fall, gradually reduce watering. When the night temperature falls below 50ºF (10ºC) water only enough to keep canes from shriveling - about 2 or 3 times per month should be enough. When night temperature falls below 41ºF (5ºC), keep the plants dry; never overwater. If you have a glasshouse in which night temperature in winter can be kept about 59ºF (15ºC), water lightly whenever plants are dry.
FertilizingAs mentioned earlier, low nitrogen fertilizer should be used for flowering plants. Be sure to stop fertilizing after early August if you wish to have many flowers.
For small plants grown without supplemental heat and where night temperature falls below 46ºF (8ºC) in winter, apply fertilizer high in nitrogen when night temperature in winter is over 50ºF (10ºC) then fertilize from January. The easiest way to fertilize small plants is by use of slow release fertilizers which are effective for more than half a year.
LightFor small plants, no shade is required in winter; 30% to 40% shade is needed from late spring for good growth and beautiful canes and leaves.
For medium or flowering size plants, no shade is necessary all year; plants will grow vigorously and bloom profusely.
In case there is hardly any breeze, about 30% shade is needed only in summer. If ventilation is inadequate in the greenhouse during the flowering season, buds will be damaged and flowering will be poor. Therefore, 30% shade is recommended from the time buds appear until the end of the flowering season. However, no shade is needed if temperature is low and sunlight is weak.
If you follow these cultural hints for nobile type dendrobiums, your appreciation of dendrobiums will change. You will be charmed by the beauty of nobile type dendrobiums.
Flowering plantsWhen grown properly nobile dendrobiums will reward you with heavy textured, big, bright, deep colored flowers which last a long time. Yellow or orange colored flowers require 7 to 10 days to attain deep rich colors. Wait until flowers mature moving plants from greenhouse to cool areas where you can admire and enjoy the flowers.
When in full bloom flowers will last longer if plant is placed in a cool, dry spot away from any draft and direct sunlight. A night temperature of 40º to 50ºF (5-10ºC) is ideal. Water the plant enough to moisten the surface of the medium once every 10 days during the warmest part of the day. With the right amount of moisture, plants should dry before evening.
If culture is poor or roots are damaged, flowers will be small, faded and of poor texture. If temperature is too high - above 85ºF (30ºC) day and 70ºF (20ºC) night - after buds are formed, flowers will be soft.
Repotting after floweringOvergrown or large plants which have finished flowering should be divided and repotted. This should be done only when night temperatures remain about 55ºF (13ºC). In case lower temperature prevail, transplanting should be deferred. To repot, remove decayed medium and discolored, black or decayed roots, pot the plant into a smaller size container. If the root ball has decreased due to removal of decayed roots. Repot into a larger size container.
Only plants with more than 7 or 8 canes should be divided. If healthy plants with only 4 or 5 canes are divided, the following year's growth will be poor.
Transplanting small or medium size plants which have finished flowering should be done only when the pot has become too small to support the height of the canes.
After repotting, plants should be kept relatively dry for two weeks. Water once every 3 ro 4 days just to moisten the surface of the medium. When new roots appear the plant should be given ample water to soak through the bottom of the pot. The plants should be kept in 40% shade and away from direct sun for about 3 weeks after transplanting.
From spring to early summer, offshoots (keikis) may appear on the upper nodes of canes due to damage of new shoots breaking or by slugs or to excessive application of nitrogen. The offshoots which appear in spring will produce thick canes and mature during the summer. When roots are 2-3.5" long (7-10cm), the offshoot can be removed from the cane. Soak the offshoot in water to soften the roots and plant in 3" or other size pot depending on size of offshoot.