Dendrobium culture: No, its not dead.

For most orchid growers nowadays, Phalaenopsis are the gateway drug to bigger and more expensive plants.  But the Phalaenopsis that are now widely available are the product of many decades of hybridizing toward producing a plant that will survive in the average home even when (shudder of horror), watered with ice cubes.   Orchids species are an entirely different beast.  With 30,000 species (at least) species orchids show growing patterns and seasonal cycles very different from your average hardware store Phalaenopsis.   That is why it is important to read about the plants you buy.  A lot of orchid growers do impulse buying and then are bewildered by the way their plants react. 

 An example of a plant that can confuse a novice grower that is trying species is Dendrobium devonianum.  It produces slim canes that can be almost a meter long.  Unlike the leaves of Phalaenopsis, the leaves of Den. devonianum are slim, delicate and are soon deciduous.   During the growing season a cane of this species has leaves near the growing end of the cane with the rest quite bare.   When the cane stops growing, it eventually sheds all its leaves and for months afterwards it looks like its dead.    If the canes have been exposed to strong light and have developed a purplish color, they can look even worse.

This is an adaptation to the cold dry season when the trees lose their leaves and it rains little.  The orchids then have to endure months of drought and harsh sunlight.   My plant blooms in April, just before the local rainy season starts.  For months it looks like a mass of dead and shriveled stems.   But this is deceptive.  In the nodes of those leafless stems the flower buds are maturing.  A well flowered plant is quite impressive.

If you look at the top photo, the orchid looks like its in a wretched condition, ready to be thrown into the trash can.   But if you look closely, you can see the remains of many inflorescences in the second longest cane.   Note the very small root ball.  That is not unusual, if a plant is well fed and watered it will produce just the minimum of roots it needs to fill its needs.   In the bottom photo you can see the cane covered with flowers.

Dendrobium anosmum and its relatives, the rest period as a tool to promote abundant blooming

Dendrobium primulinum stems at the tail end of the growing season

The same plant as above after two months of no water or fertilizer and exposure
to bright light.

Dendrobium Adrastra blooming from leaveless canes

A properly rested plant of Den, anosmum with more than forty buds in a single cane.  Note the blooms are produced all along the lenght of the stem and not just near the tip

A relatively young Den. primulinum plant, note that stems are plump and still have the remains of a few leaves.  See below the plant in full bloom.

Giving your Dendrobium a rest period can be the difference between an impressive and abundant floral display and one that produces just a few blooms.  Species of Dendrobium of the group that includes  anosmun, primulinum, cucullatum, nobile and parishii among others flower best when given a rest period that mimics the seasonal conditions that are the trigger for blooming in their native haunts.

What is the nature of the seasonal rest period in this particular group of orchids?  These Dendrobium live in the south east of Asia and in parts of India.  In these regions they are subjected to the monsoon weather system.  In the summer there is abundant rains that fuel the growth of their long pendent canes.  But as winter approaches the rain diminishes considerably and eventually ceases for some months.  The constant cloudiness of the monsoon season is then substituted by clear sunny skies.   As the rain ceases the trees lose their leaves and the Dendrobium are exposed to high levels of sunlight.  Finally as the dry season starts the Dendrobium lose their leaves and enter the dry season as a bundle of stems that not in the least resemble their lush rainy season appearance.

Generally, but not in every geographical region, the dry season is also a season of lower temperatures.  The combination of high light conditions, drought and low temperatures is said to prime the buds of the stem of many Dendrobium for flowering. That means that the seasonal change is the cue that makes the vegetative buds that are all along the stems turn into flower buds.   When orchidists talk about giving their plants a rest period they are referring to the set of circumstances in the natural habitat of the Dendrobium that I have outlined in the preceding paragraphs.

Personally I stop all fertilizing and watering in November.  This means that the media of some of my plants will become bone dry and stay that way sometimes for several weeks.  All my pendent Dendrobium tolerate these lengthy dry spells with little complain, probably because even thought they are not getting any water the environmental humidity is high enough to prevent severe shriveling of the canes.  However I do have to confess that if I see a plant becoming excessively wrinkled from desiccation I do water it lightly.

 Although these conditions might seem severe and some of these pendent Dendrobium will flower quite well without experiencing the most severe rigors of the rest season other species will not produce flowers if not given a distinct rest period.  The best example of an orchid of this group that grows very well and yet blooms poor in the tropics is Dendrobium nobile.  If maintained under constant warm conditions, fertilized all year and kept under shady conditions most nobile will bloom poorly and may not bloom at all.  

Some orchidist just can’t resist the urge to water and give fertilizer to their plants year round. These orchidists generally have a tough time getting blooms out of them.  I have seen massive nobile specimens that have never produced a single flower.  I once brought a large plant for the ridiculous amount of $15.00 because the garden store owner had become tired of waiting for it to bloom and felt the plant was taking too much space and not bringing any profit.   I gave this plant a proper rest period and the plant responded by producing 150 large and fragrant flowers in about twenty canes.  All those canes that had accumulated without blooming for years produced flowers all at the same time.

I know some people keep watering their plants even in the rest period and that some of those plants bloom from canes that have kept their leaves.  But so far I have not seen a plant that has kept its leaves bloom as abundantly as one that has lost all its leaves due to the stress of the rest period.