MANILA, Philippines - Cane-type Dendrobiums are the most popular orchid cultivated in the Philippines. Generally the plants are bought when they are in bloom and more often than not, the plant deteriorates in the hands of the home growers. This condition has been described as “Dendrobium Orchid Decline” during the 80’s.
The sequence of events that lead to “orchid decline” are as follows: Orchid nursery grows the plants fast with steady increase in height of succeeding pseudobulbs; Plants flower as soon as they reach a particular height depending on the genetic make-up of the plant; While the flowers are intact, vegetative growth slows down because the plant need to divert some of its food (photosynthates) produced to the expanding flower tissues;
Since the fertilization programs for these commercial orchids are heavy, homeowners who buy the plants may not be able to keep up the feeding regime; The next pseudobulb growth are usually shorter than the previous ones; As plant grows more pseudobulbs, the older canes tend to lose their leaves leaving only the youngest cane with leaves and live roots; As the plant grows older, flower quality and quantity diminishes and new plants progressively shrink in size;
Aggravating Factors to Dendrobium Orchid Decline
– Age of the plant. Older plants tend to have more leafless pseudobulbs (generally non-photosynthesizing) to be nourished by the remaining photosynthesizing leaves; It may be said that the pseudobulbs are parasitizing on the young healthier photosynthesizing portions of the plant; As the plant ages, the system becomes less and less efficient because of ever-increasing leafless pseudo-bulbs and therefore more load for the leafy areas to carry or feed;
– Media degradation. Commercial Dendrobium growers plant Dendrobiums in Coconut husks. The cocohusk chunks are perfect for 9 to 12 months growth cycle of Dendrobium (growing to blooming). After blooming, the home growers are suppose to change the potting media; The old medium breaks down and acidifies and becomes very water retentive. Waterlogged media damage the epiphytic roots of the plant resulting in rotting of roots followed by defoliation of the pseudo-bulb corresponding to the damaged roots. In advanced stage, the pseudo-bulbs shrivel up then turn yellow. Damaged root system promotes keiki production;
– Fertilizer application. The Dendrobium roots are designed for low levels of fertilizers and may easily be damaged by dumping strong fertilizer solutions on the roots. The leaves however can take very high concentrations of fertilizers without damage. Applying strong solutions foliar fertilizers directly to the root system damage the root system in the shortest possible time.
– Keiki or Anak production. Pseudobulbs with damaged root system defoliate then send off plantlets. The more plantlets, the more exhaustion of food and water reserves in the pseudobulbs.
Solution for Dendrobium Orchid Decline
There is only one solution to Dendrobium Orchid Decline: that is plant rejuvenation. Rejuvenation is done by trimming off as many inefficient leafless canes leaving only one or two attached to the leafy cane (for better anchorage). By systematically trimming off leafless canes, the plant system becomes more efficient and will tend to grow faster.
The leafless pseudobulbs will have enough food storage to produce plantlets which may be planted when big enough to handle.