Dendrobium culture: Dendrobium Mentor 2023 growing season

 

This Dendrobium is a hybrid of Den primulinum and Den anosmum.  This plant is from a remake, the original hybrid was made in 1893.   This plant is attached to the bottom of a custom-made wire basket.  As you must have noted from my posts on orchid culture, I prefer to grow these pendent orchids attached to the bottom of wire baskets.   I do this because when these plants become larger the canes tend to outweigh the pot many times, even when potted in a heavy terracotta pot.  As a result the pots lean to the side, making watering and fertilizer more difficult than usual.   Also these plants are heavy feeders which tends to deteriorate the potting material at an accelerated pace in a pot.  In a wire basket the media stays sopping wet for only brief moments with helps control the bacteria and fungi that destroy potting material.

My plant of Dendrobium Mentor tends to favor the primulinum parent in regards to plant form.  The canes grow almost horizontal, in the direction of the strongest light, until they grow to a size that makes their weight force them into a vertical alignment.   My plant needs heavy fertilizing during the growing season and daily watering to get the best rate of growth.  It also needs strong light.  I have it in a place where it gets full sunlight for a few hours each day between 8 am and 11 am.   In primulinum, the best flowers I have seen were in canes that were exposed to so much sunlight that they were purple.    At this moment, in August, the plant is about halfway to its final size which it will reach December.

 My Dendrobium anosmum plants shed their leaves in December.  I have not paid attention to when Dendrobium Mentor becomes deciduous.  In my garden, this orchid blooms in March or April.  I was slightly disappointed that the two adult canes of my plant bloomed at slightly different times in 2023.  This year the plant has three canes that have the potential to reach blooming size.  The best outcome will be for the to open their flowers all at the same time.  This orchid produces a single flower from each flowering node.

 Den Mentor is fragrant in my garden, although its fragrance is not as powerful as that of Den. anosmum.   The fragrance is subtly different from the sweet smell of Den. anosmum, but I lack the training to give an exact description of the fragrance.   I find its fragrance pleasing.

 As can be seen in the photo above the plant has a few keikis.  These will be removed and planted separately at the start of the next dry season, when the plant is dormant.  Some keikis will be removed along with the cane they are growing from to give them a sizeable reserve of water and nutrients to fall back on when they are producing their next year growth and roots.

Dendrobium Culture: Making a Den cretaceum specimen plant

 

Some years ago, I started cultivating a Dendrobium cretaceum plant with the aim of eventually getting a specimen plant with many flowers.  For aesthetic reasons I decided to cultivate the plant so that the canes hang from the bottom of the basket.   The orchid is planted in a way that is extremely different from what is the usual way of growing Dendrobium.   The plant was originally attached to the center of the bottom of the basket.  That way the roots would grow up into the potting mix and the canes would grow downward.   That is the exact opposite of how these plants are grown.    The basket is six inches wide and three and a half inch deep.  The potting media is bark, and fills the basket to a depth of two inches.   Den cretaceum is not a big plant so this arrangement allows plenty of space for it to grow for years.

There two-inch layer of media in the basket allows for plenty of air to reach the roots.   This is a very important detail.  You would think that is a very small quantity of media for a plant that one eventually wants to become large and bushy.  But due to the local climatic conditions it is the perfect amount.  The reason is that during summer and fall in my locality it rains almost daily.   At the peak of the rainy season the media can stay wet for weeks or months.   In a plastic pot this would mean a waterlogged media that would quickly become devoid of oxygen, will start rotting and turning into slush under the influence of fungi, bacteria, high temperatures and fertilizer.  

 To my delight, at the start of the 2023 growing season the plant, that usually produces four or five new canes every year, in a fit of exuberance, started producing nine new canes.   This is wonderful but it bring its own suit of problems.   First, all the canes are clustered and oriented toward the strongest source of light.   That means that the plant is self-shading.   This can result in that some of the canes will be spindlier and weaker.   To avoid that I moved the plant to a spot where it gets the strongest sunlight I can give it without burning the leaves.  Eventually as they grow the canes will spread out and the issue will resolve itself.  Because of the particular way the canes of Den cretaceum grow the leaves are not particularly vulnerable to burn if exposed to strong light.  The canes of this orchid arch downward, so that when the sun is at its strongest the leaves are edge on to the light.   A note of warning, while canes are capable of taking full sunlight, the base of the canes are prone to burning if exposed to very strong sunlight.  Fortunately, this is not a problem for me since the basket protects the tender bases from the sunlight.

If all goes well, by the start of the 2024 dry season, the canes will have reached their full size.  When the canes reach full size, I stop watering and fertilizing the plant, it gets only the scant amount of rain we get during the dry season.  The plant loses all its leaves and looks dead for a time.   In April I will start looking for the swelling flower buds along the length of the canes.  Then in May I expect the plant to produce a mass of flowers.  You can see on top the 2023 blooming.   The plant as it is now is in the photo below.

Dendrobium primulinum (now known as Den. polyanthum)

These photos are of a flower that that was just opened.  The flower will expand a bit in the first few days after it opens.  Dendrobium primulinum is a variable species with a vast geographica distribution, but all its forms share the characteristic of a lip that is almost round and very large in comparison with the rest of the floral segments.

Dendrobium polyanthum aka Dendrobium primulinum var. Laos, the flowers of two different clones.

About a decade ago there was a large importation of plants of Dendrobium polyanthum to the island of Puerto Rico, in fact they also seem to have been sold in the United States.  Some ot these plants have survived and bloomed.  The top photo is a flower from a plant that I grew from a keiki.  The flower has a large yellow area in the labellum.  The bottom flower is from a plant that I brought as an adult, the area of yellow is smaller than in the flower on top but the labellum is larger.  The plant that produced the flower on top is a slow deliberate grower that is somewhat delicate, the plant that produced the flower on the bottom is a vigorous grower and blooms relatively well.

Dendrobium polyanthum Wall. ex Lindl. 1830 a rewarding species to grow

In 2007 it produced five flowers

By 2011 it had improved a little

The first time I saw the flowers of this orchid I was absolutely entranced by their beauty.  The plant I took home with me had a single adult cane and the first time it bloomed it produced only five flowers.  But the beauty of the flowers was such that even those few were well worth the effort.  In time, as you can see, it eventually produced a few more flowers.  You can read more about my experience with this species here:

 http://ricardogupi.blogspot.com/2010/10/dendrobium-primulinum-also-known-now-as.html

Dendrobium cretaceum, now considered to be Den. polyanthum

I brought this species two years ago and it has proven to be a reliable bloomer that seems not to be bothered by hot weather.  My plant has grown well with no special care.  As you can see it has bloomed the lenght of the cane, not something that is common here when dealing with Dendrobium that come from the north of India and the Himalayas.   The flowers last well if protected from insects.  Thrips in particular are a problem as they are mightly attracted to these flowers, probably due to their white color. 

In the past I saw some plants of this species labeled as Dendrobium primulinum var. alba.  The name polyanthum has precedence over the name cretaceum for these plants.  O have used the name cretaceum because many plants have been sold under his name. This plant was unknown in local orchid circles until fairly recently.  The first person I knew that cultivated and bloomed it was Dr. Julio Rios.  Since then this plant has been imported into the island and seems to be doing well in local collections.

Dendrobium primulinum 'DeLeon' an interesting plant

Flower with nearly round lip

flower with a very small scoop like lip

Large flower with oblong lip that has a ridge in the middle

This is a flower that is just opening it will expand until it look that the one in the photo over this one

A fairly good blooming althought the presentation is not the best

Large plant growing in a fairly small wire basket

I brought this interesting Dendrobium a few years ago from Eli Orchids in Utuado, a town in the mountainous interior of the island of Puerto Rico. When I got this plant it was labeled as Dendrobium primulinum var. Leon and for lack of a better name I kept this ID and photos of this plant taken by me can be seen in several orchid forums. However when it bloomed the flowers were oddly different from what most books and Internet photos identified as typical primulinum. I found photos of flowers that had some resemblance to those of my plant, the flowers were those of variety Assamicum. However on closer inspection the resemblance proved to be superficial. Compounding the problem of identification was the strange proclivity of this plant to produce flowers of widely differing sizes and shapes. Even worse some flowers expand quite a bit and may look one way freshly opened and another after they have been open for a week. A few days ago, with the help of Brian Monk who answered a question I posted in the Orchid Source forum, I finally learned that the true identity of my plant is Dendrobium primulinum DeLeon.

But the doubt I had about this plant identity plant, when I first bloomed it, piqued my curiosity so I studied scientific descriptions of the flowers of primulinum to better understand this plant. What I found is that the appearance of the flowers of this species is more variable in color and shape than one would guess judging from the characteristic of those exhibited and grown in the United States. The plants in the US, at least judging from photos of collections and exhibitions used to be, until recently, relatively uniform in appearance. I would like to add that primulinum now has been lumped with cretaceum and the plants are called Dendrobium polyanthum.

The form of primulinum commonly pictured in those books and photos that have been available to me has thick, arched canes that are relatively short. The flowers in these plants have hairy lips of a light yellow color, the sepals and petals are varied shades of mauve. In the lip, usually to the side of the column there are purple lines that have a varying extent in different clones. I have occasionally seen plants of this type in local collections, but I have never seen one in bloom anywhere in PR.

About four years ago a new type of primulinum appeared locally. This new type was part of a huge importation of all types of Dendrobium for the spring show of the PR Orchid Society show. It is clear plants of this type were also imported into the US as photos of the flowers of plants of this type cropped up in the Orchid Source forum. This new type has large flowers with a beautiful bright yellow color covering the center of a white lip, the sepals and petals were a delightful soft pink. But this new plant didn’t resemble DeLeon at all. The vegetative parts of this plant were different from De Leon and the thick short canes of the primulinum I had known previously. This plant resembles those plants known in Japan as var. giganteum.

Information on primulinum DeLeon is pretty sparse. I did several Internet searched and frustratingly and vexingly the results of the searches were either posts that I had made about this plant on the various Internet orchid growing forums or the advertisements of the vendor that sold me this plant. Thanks to Brian Monk I learned that this plant earned a certificate of cultural merit for its owner back in 1968, the plant exhibited had 101 flowers.

My plants grow well without any special treatment but are curiously varied in their blooming. This is a bit surprising since all are descendants of the same plant. Some produce large flowers with huge round white lips other produce smaller flowers. At times a cane can have large flowers near the top and smaller flowers near the tip. The lips of some of the flowers are very round others are oblong and some even have a ridge down the middle. It is unclear what causes this variation in the flowers but in general older plants with several older mature canes produce better flowers than younger plants with just a few small canes. A peculiar characteristic of this plant is that the first few leaves of the new canes can have a bright reddish or purplish tint in the margins, this I have not seen in any other Dendrobium of this type that I have grown.

This plant doesn’t seem to need much rooting media to subtract enough water and nutrients to prosper an achieve a good size. One of my plant has six healthy new canes from three to four feet of lenght and several older canes all growing from a mass of media two inches thick and six inches wide. However it is to be noted that this plant gets drenched every day during summer and fertilized weekly for as long as the canes are producing new leaves. This plant usually finished its growth cycle October and starts shedding its leaves by November.

Some years the plants blooms wonderfully, others they barely produce one flower or two. But I enjoy so much the flowers when they are produced that I don’t mind the fact that some years some plant fail to bloom. I have been looking at the wonderful plants that have been awarded in Japan and I have realized that the flowers of my plants would look even better if I did some grooming of the canes before the buds open to prevent crowding of the blooms. I am looking forward to next year blooming to see if I can make the 2011 blooming the most beautiful and elegant ever.

Dendrobium primulinum, also known now as Den. polyanthum

I have had Dendrobium primulinum for about five years and I have found it is among the most beautiful and easy to grow of all Dendrobium. Unfortunately easy to grow doesn't necessarily means it is also easy to bloom. All the plants I have brought have grown well with what I consider standard care for members of the Dendrobium section of the genus Dendrobium. However getting these plants to bloom has been at times a source of frustration and disappointment. It appears that I am growing this species at the very upper limit range of their temperature tolerance for blooming. That means that relatively small variations on the night temperatures at certain critical parts of the year can have profound influence on the quality and quantity of the blooming.


Growers that grow primulinum in the lowland coastal plains of Puerto Rico report that the plants bloom with few flowers or even a single one. Other plants may fail to bloom at all. Irma Selles,a well known local orchidist or renowned skill growing plants showed in an Internet forum a large healthy plant with only a single flower. Dr. Julio David Rios, an accomplished grower of many types of orchids says that his primulinum plant has never bloomed. Don Alfonso a Mayaguez grower that had a large collection of orchids in the seventies and eighties that had a plant of primulinum var. giganteum for many years would complain that his plants bloomed very rarely and often would produce just a single flower. All the plants in the previously cited cases are growing under a climatic regime where night temperatures rarely fall much under 75F at night even at the depth of the tropical winter (which actually is not that cold and could be more properly regarded as the dry season). Where I live, in the mountainous interior of the island, at a height of about a 1,000 feet, temperatures fall to the top sixties at night in winter and may go down to the high fifties for a few nights during the coldest part of the year.
This 10 degree difference between the night temperatures in the coast and the interior makes all the difference in blooming primulinum. But it has to be said that even thought my plants bloom better than the plants in the coast, they could probably bloom even better if the temperatures dropped down consistently into the fifties. I know this because I have seen photos of primulinum growing outdoors in Hong Kong, China and there they produce many more flowers in a single cane than plants in Puerto Rico. In the year 2009 my plant bloomed poorly, with the exception of a single cane that produced two flowers all the other canes failed to bloom. Some of my primulinum, a plant labeled var. Leon, seems to be less sensitive to excessive warmth, however even this plant has, on occasion, failed to bloom.  So if you have cool winters where temperature dips into the fifties and forties, and you also have sunny, warm and wet summers, this plant will probably do well for you.

I have my plants in a place where they get full sun during the morning. Due to the orientation of the shadehouse where they are growing they get more sun as autumn goes into winter, this is similar to what happens in their native habitat where they are exposed to brighter light conditions when the trees where they live lose their leaves.
My plants are watered daily from May to November and then the watering frequency tampers down until they may not get water for two or three weeks at the height of the dry season. I watch the canes and if they get too wrinkled I water the plant lightly.
During their growth phase, in my garden it is from May to November, I fertilize every week. I also put a few pieces of dry cow or horse manure on top of the media, this seems to help produce larger canes. Because the plants are grown outdoors and get a good deal of rain I don’t worry about fertilizer salts build up on the baskets where they are grown.

I grow them on plastic and wire baskets that allow for excellent exposure to air of the roots. The roots die if deprived of oxygen and this can spell doom for a plant. My plants are grown hanging from the bottom of the baskets, this allows for a more natural presentation of the flowers and in my view for easier watering and fertilizing. I don’t grow my plants in plaques of any kind as local conditions means that they dry up very fast necessitating too frequent watering.
They seem to grow well in all the media I have tried bark, cork and coconut. I would guess that these plants will grow well in most orchid planting media as long as watering and fertilizing is done taking in account the properties of the media.
I have three types of primulinum, one has bluish petals and sepals and a white lip, another has al white lip with two yellow eyes and baby pink sepals and petals. The flower of the third type I have has so much yellow in the lip that it resembles a Dendrobium farmeri flower, the petals and sepals of this flower are light pink. I have heard about some plants that have been offered for sale as primulinum alba, but the ones I have seen appear to be white individuals of a similar species Dendrobium cretaceum.
Although primulinum has very beautiful flowers, if care is not taken to groom the plant the flowers can suffer from a poor presentation. This mainly consists of flowers in each side of a cane pointing in opposite directions and flowers from different canes getting all bunched up. I have seen photos of plants exhibited in orchid shows in Asia, in particular in Japan and Taiwan which were groomed with skill that the intrinsic beauty of the flowers was greatly enhanced by the delight artistry of the presentation.

When my plants bloom next year I will try to emulate the high standards set by exhibitors in Asia to make my plants a living work of Art. Wish me luck!

Notice the excellent presentation with all the flowers pointing to the same side

An unusually dark blooming of var. Leon

Note the huge round lip characteristic of this species