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. 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. This article will focus on those plants.
Light:
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 tiny plantlets on older canes (called keikis) often means the plant
isn't getting enough light. These keikis can be potted up individually
after they develop roots.
Water:
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. After
the growing season, cut water back somewhat (maybe every ten days), but
do not suspend watering.
Fertilizer:
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:
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
at all times, although experience has shown they can withstand a few
nights down to 50 or so. But this should be avoided if possible. A
slight drop in nighttime temperature will often stimulate a bloom.
Blooming:
These
bloom for me throughout the year, depending on conditions. To help
provoke a flower spike, slightly drop the water and nighttime
temperature. Also, if a cane loses all its leaves, don't cut it off—they
sometimes bloom from old canes. The flowers are long-lasting, up to six
weeks.
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. These plants are shipped
in quantity from Hawaii, Taiwan and throughout Asia, and some growers
have started selling them grown in wood chunks. This is my least
favorite potting situation because the plants are often top heavy and
the wood gradually rots away. I prefer a mixture of clay aggregate,
perlite, and coconut fiber. Repot at the beginning of the growing season
when necessary.
Grower's Tips:
I was
initially confounded by these plants. I had several, and killed many,
and could never coax them to bloom. I soon figured out my mistake: I was
treating them like phalaenopsis. With the dendrobium phalaenopsis
hybrids, think more of everything: more light, more water and more
fertilizer. They are robust growers that send up at least one new
upright can every year from creeping rhizomes. Don't cut off old canes
as they will sometimes flower or produce keikis that can be potted up on
their own.
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