Tuesday, February 15, 2011

Dendrobium harveyanum, an orchid with canary yellow flowers and unique fringed petals

A freshly opened flower

Front and side view of the flowers

A fully expanded flower
An inflorescence with fully expanded flowers, the inflorescence is wet due to a hard rain 
A cute little species with unique flowers
                Dendrobium harveyanum Rchb. f. is a small statured species that produces canary yellow flowers with densely fringed petals.  The fringed petals are a salient characteristic of this species and make it unique in the Dendrobium group.  Many species have fringed, hairy lips, but with the exception of rare cultivars of Rhyncholaelia digbyana that have slightly fringed petals, no other species has petals like Den. harveyanum. 
                 When I first became aware of this species owning it seemed like an impossible, unrealizable dream.  It is found in the wild in Burma, Thailand, Vietnam and China and all sources agree that it is a rare in the wild.  Even in cultivation the plant didn’t seem to be plentiful and in those pre-Internet days even photos of it were not often seen.  But those few photos that I found convinced me that this species was well worth the effort of cultivating if it ever became available.
                In 2006 a US orchid vendor announced the availability of seedlings of this species and I promptly ordered three.  When I received the plants they had canes of two to three inches of height.  The height of mature canes of this plant is between six and nine inches to it could be said that even though the plants seemed small they were already well developed for their species.
                I planted the seedlings in wire baskets three inches wide by four inches deep.  The potting media was small sized bark.  Growing these plants in wire baskets ensured that the roots would get plenty of access to air.  Giving the roots access to oxygen a critical factor in the culture of many Dendrobium which tend to deteriorate and die in cultivation because they are intolerant of deeply packed and poorly ventilated media.
                The plants are grown outdoors in an open terrace that receives full sun for two or three hours between eight and eleven am.  After that it gets sunlight filtered through the trees.  New leaves in my plants display a pleasing wine coloring when they are developing probably in response to the high light levels of the early morning.
                Local temperatures fluctuate between 85 F and 75 F at the height of summer and 75 F to 65 F in the coldest part of winter.   For a few weeks in summer temperatures can go over 85 and even into the nineties. For a few weeks in winter temperatures can go under 65F but this plant doesn’t seem to be bothered in the least by either the hot or the cold end of the temperature spectrum.
                The plants were watered daily when they were producing new canes and fertilized with a high nitrogen fertilizer once a week.   When the canes were almost fully grown the applications of fertilizer are stopped.  No fertilizer is given when the plant is not producing new canes.  Local humidity varies with the seasons, it fluctuates between 40% and 90% during the day in the dry season but in the wet season it always stays over 70% and in particularly rainy parts of the wet season it can get close to a 100% nightly for many weeks.
                In Puerto Rico, which is in the tropics, we have a dry season that lasts from January to April.  During this time of the year I water the plants lightly once a week to mimic the effects of the rest period they would get in their native forests.  The canes of the plant become furrowed but otherwise the plants seem little affected by the decrease in watering frequency.  I start watering and fertilizing as soon as I notice new canes growing from the base of the previous year canes.
My experience growing this plant has been complex due to the different way the three plants I brought fared under my care.  The three plants were small seedlings when they I received them.  One of them started growing vigorously and quickly reached a height of six inches which is the maximum size they have attained under my care.  Another plant has produced canes of about four inches in height but no bigger.  One plant grew weakly became infected with a bacterial or fungus rot and almost died, it has remained small with canes about two inches tall.  All of the plants have bloomed, even the tiny one.  The only one that blooms every year is the tallest.
I know this orchid can reach sizes larger than those of my plants but there seem to be some local factor that is constraining their growth.  At the moment it is not clear what this factor is but my suspicion is that that the local conditions are a bit on the hot side for this species, and that it would fare better if it didn’t have to endure the high, into the nineties, temperatures of the local summer.
To my surprise one of my plants has produced keikis, something that is not often seen in this type of Dendrobium.  The keiki formed in a cane whose base rotted away.  They are growing quite well on bark and are treated the same way as the adult plants.  The tiny canes of the keikis are fat and short, not so similar to the adult cane.  In my other Dendrobium of a similar cane configuration I have never seen a single keiki even when every bud at the base of the cane has died.
This Dendrobium is a wondeful miniature that will amaze and delight friends and visitors with its beautiful and peculiar flowers.  The flowers are unfortunately short lived, they last a week at most under my conditions, and perhaps it’s the high local temperatures that shorten the lifespan of the flowers.  I advice protecting the flowers from rain as hard rain can give these fuzzy flowers a bad hair day and spoil somewhat their “hairdo”.  The flowers have a honey fragrance.
Sometimes when you see a plant labeled as “rare” you think it might be difficult to cultivate and reluctant to bloom, but in this case this has not been true.   Local insects have not bothered my plants and, with the exception of the rot that attacked the smaller plant and one of the old canes, the plants don’t seem to be too vulnerable to the local bacteria and fungus. 

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