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.

Dendrobium Adastra a hybrid of anosmum and cucullatum

I brought this plant many years ago in a Puerto Rico Orchid Society show at el Coliseito Pedrin Zorrilla.  When I brought the plant it didn’t have an ID but given its distinct flowers it was easy to identify it using the sources available over the Internet.  This orchid is a hybrid of Dendrobium anosmum and Dendrobium cucullatum (pierardii).  I have seen a number of plants of this hybrid and there is a certain degree of variation on flower size, the color has been the same in all the flowers.  The plants I have seen fall into two broad types, the ones that favor the flower size of the anosmum parent and the ones that are on the cucullatum parent side of the spectrum.  The plants that have flowers that are more similar in size to anosmum tend to produce less flowers that the ones that favor cucullatum, which has smaller flowers.  I personally like the type that produces the smaller flowers.  None of the plants I have seen have had any fragrance that I could detect. 

This plant is a vigorous grower under my local climatic conditions and the care it receives is the same that my anosmum plants are given http://ricardogupi.blogspot.com/2008/10/dendrobium-anosmum-when-cultured-so.html.

To my surprise I have found that my clone of this plant is less tolerant of exposure to full sun than the clones I have of the parental species.  Plants grown with an exposure to a few hours of morning sun are smaller and weaker that those that are under shadier conditions.  It is unclear whether this is a result of an endemic susceptibility of this hybrid or a particularity of my clone.

My plant produces flowers that are brightly colored when they open but that become lighter in color as they age.  As a result the plants are at their most beautiful in the first few days after the flowers open.  My clone of this hybrid produces canes that are shorter than those of most anosmum and cucullatum clones I have even though it is grown under the same conditions that they are.   Since some of my cucullatum and anosmum plants can produce six feet long canes I can only surmise the plants that were used as parents for this hybrid were of a smaller stature. This plant produces keikis fairly frequently in older canes and the keikis grow well with routine care.  Sometimes the base of the older canes succumbs to rot but the rest of the cane stays alive.  When this happens I put the cane in a shady and humid area and very often the cane will produce one or more keikis.

Dendrobium anosmum and their relatives, warning signs of cultural trouble

Vigorous and healthy root growth, note that the cane producing the roots is twice as thick as the previous growth

New roots are white older ones are grey green, absence of root growth is a clear signal of trouble

Fungal and bacterial infections can strike with astonishing speed and virulence, this is all that remained of a specimen plant of Dendrobium formosum var. giganteum.  If the gravity of the situation had been recognized on time at least some pices would have been saved for propagation

This Dendrobium nobile has been growing for many years in an avocado tree under hot tropical conditions.  It has never bloomed although in all aspects it is mature plant fully capable of blooming.

Dendrobium nobile blooming in a shady and cool location.

A Dendrobium phalaenopsis derived hybrid which lost all its roots due to inappropiate potting, all the old roots are dead but some new roots are showing their tips near the base of the canes.

The buds at the base of this canes are dead so the plant is producing new growths from buds higher up in the cane.

The base of these canes of Den. primulinum was damaged by sunburn and died.     The canes were bent so that the keikis produced by them can attach themselves to the basket.  Notice the many keikis and their abundant root growth.

Den. phalaenopsis hybrid grown with its roots exposed.  Note the abundant flower production and the fully leafed new cane.  It is normal for older canes to lose their leaves after the first year.

Under good care some keikis will bloom even when they are not affixed to anything

When they are growing at their preferred temperature and lighting range, well cared pendent dendrobiums grow vigorously, without any particular trouble and bloom reasonably well. But when they are grown under conditions that are unsuitable for them several things happen that serve as a warning signs that the plant is not doing well. I will detail some that I have learned from the bitterest experience. This is a work in progress and I will try to add information as time permits.

I. When your plant needs a colder rest period to bloom than you can provide.

If a plant needs a colder rest period to bloom but otherwise the conditions are to its liking you will get an endless production of handsome canes, which will be plump and healthy but will never bloom or even get in bud. Because circumstances prevent them from blooming these plants channel their energy into growth and can produce quite large plants. One Den. chrysanthum I have eventually produced a ten feet long cane. This particular plant has never produced even a single bud under the local climatical conditions. Dendrobium nobile will not usually bloom in coastal Puerto Rico but will bloom nicely if moved to locations about a 1,000 feet high in the mountain areas and in certain colder inland areas. There are plants here and there that bloom under conditions that are not in their usual preferred range but usually they do so erratically or poorly.

II. When the temperature is not in the preferred range for growth.

The first signs of trouble in this case is usually a lack of root growth. Unfortunately some pendent dendrobiums can survive for many years growing weakly and with root systems that barely sustain whatever meagre growth they manage. It can happen that the plants perk up and do produce good growth during brief times when conditions are to their liking, but as soon as temperatures drift out of their preferred range the plants weaken again. I brought a Den. falconeri that managed to survive ten years by growing acceptably during the brief weeks that local temperatures dipped and then sulking the rest of the year. Strenuous efforts to sustain this plant only lengthened the agony. Eventually the plant dissolved into a mass of tiny canes and diminutive keikis that were too weak to survive the summers heat. Keiki production on a a same year growth is also a very bad warning sign. It usually means that the plant inability to produce roots has made it transfer its energy to keiki production.

III. When it is not getting enough sunlight

If your plant is not getting enough sunlight to bloom properly you will probably get a few blooms right on the tip of the cane. A plant that might produce dozens of blooms might only produce two or three. The canes themselves might get to be abnormally long and thin. The leaves will have a deep green color.

IV. When roots are not entering the potting mix, or holding the mount.

This probably mean the mix is unsuitable for the plant because it has some characteristic that is inhibiting or killing root growth. A friend of mine accidentally killed many of his orchids by mounting them on the wood of a plant whose wood is permeated by a substance this plant secretes to kill other plants that  might compete with it for food or sunlight.  

V. A growth coming from a cane other than last years cane, if last year cane doesn't grow.

It probably means that the base of its newer cane is dead and the plant is trying to keep alive by producing growths elsewhere. In some plants, (this is an specially insidious occurrence in pendent dendrobiums) a cane that has shed its leaves can continue attached to a dead base without any obvious signs of distress for months before decay reveals that the base is dead.

VI.When a cane suddenly stops growing in the middle of producing a new leaf.

Usually means that something has severed the connection between the growing tip and the base of the plant. I have seen this happens when an insect gnaws the middle of a cane and makes a cavity but leaves it mostly attached to the base on the sides of the cane. This can cause the death of the whole cane, not just the tip.  On some ocassions this can signal a bacterial or fungal infection of a stealthy nature that only becomes obvious when the cane starts to decay rapidly at a time when it should have been growing.

VII. Blackened and sunken areas between the base of the plant and the lower part of the cane.

Can mean sunburn to this area, can result on the death of the plant but the survival of some of the canes.

VIII. Profuse keiki production on plants that normally produce them sparingly.

A sign of root loss, or of loss of the buds at the base of the plant.

IX. A weaker cane than the previous year's cane.

Plant is not getting what it needs to grow well, common in newly repoted plants that have suffered severe root loss and plant adjusting to new environments.

All this information is courtesy of the need to unwind after an unexpedtedly streesful day at work.

Dendrobium culture: anosmum and its relatives

Dendrobium anosmum, when cultured so that they can hang down as they do in nature, can produce quite a show. Here are ten plants hanging from the roof of the terrace of my house. The fragrance was delicious, strong and could be perceived for quite some distance due to the large number of flowers open at the same time.

These plants are growing in a shade house, notice the large number of blooms per cane.

When fed well, given strong light and ample watering, Den. anosmum can produce impressively large leaves.

Den. anosmum growing in a pot made out of a plastic soda bottle. Note the large size of the plant in comparison with the pot in which it is growing. If you see the older canes you will notice that they are all smaller than the new one, this is a clue that this is a relatively young plant.

The bottom of the pot was sealed with a piece of saran shade cloth, the roots grew over the saran and into the media, notice the white color of the new roots a clear sign of health.

As a fanatic of pendent dendrobiums, I have had quite a lot of experience growing these lovely but at times very frustrating plants. Perhaps the most difficult problem I have had with these type of Dendrobium has been finding out by trial and error that some of the most beautiful species will not grow and flower under my climatic conditions. When I got them, in the dim prehistory of the pre-Internet era, there was not much information available locally on growing particular species of Dendrobium. Nowadays there is such an enormous amount of information on the Internet that a little detective work using the various search engines for finding out the proper growing conditions of the particular species you like will go a long way toward avoiding dissapointment. The pendent Dendrobium species find agreeable my local climatic conditions grow vigorously and flower abundantly. In the next lines I will share some of my experiences with these plants. My experience has been with Adrasta, aduncum, anosmun, aphyllum, loddiggessii, nobile, parishii, primulinum and tortile among others.

Light: These plants love high light and benefit from some hours of full sun, some can even stand full midday sun without complaint, however exposing the base of the canes to full sun is deathly for these plants. The base of the canes will die if sunburned, and eventually the plant will die too. It is a perplexing and surprising experience when your plant suddenly becomes a group of live canes held together by a dead base.

Watering: Everyday at the height of the growing season, drenching the pots until water flows out. When leaves start turning yellow I stop watering, (around December), when flower buds appear, in the middle of February locally I resume watering.

Fertilizing: Heavy, on plants potted upside down I put some pieces of horse manure on top of the pot.

Potting: I no longer pot my pendent dendrobiums in the top of pots, I pot them in the bottom of wire baskets and pots I make out of soda pop bottles. I started potting them upside down because I became extremely frustrated with the fact that plants eventually weighted so much they would tip the pots and make watering and fertilizing difficult. Plants can stay in these pots for many years. The first plant I potted in a soda pop bottle fifteen years ago is still growing in the same pot.

Media: These plants seem to be able to grow on anything as long as it allows for oxygenation of the roots. Every year I hose off the decayed material and add fresh one. I have used sphagnum moss, bark of all sizes, glass marbles, wood chips, tree fern, charcoal, etc. As long as the plant gets watered and fertilized appropriately for the material it seems to make no difference.Since a picture is worth a thousand words here are some showing how I pot my plants.