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Sphagnum vs fir bark

This is a discussion on Sphagnum vs fir bark within the General Orchid Culture forums, part of the Orchid Culture category; I have many phals in both sphagnum and fir bark. In the sphagnum the roots ...

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    moniluhum is offline Senior Member
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    Default Sphagnum vs fir bark

    I have many phals in both sphagnum and fir bark. In the sphagnum the roots are generally moist at all times. In fir bark the roots are not as moist to the extent of the sphagnum. Is it a good idea to let the roots in the fir bark dry out for a short period of time? What is the best watering process for phals grown in fir bark? I am doing ok with the phals. I just want to do it the best way possible.

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    I grow almost all my phals in clay pots. I run a lot of water through the pot when I water, but I let the bark dry almost all the way before watering again.
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    In my view, It depends on climatic conditions, if the environment is dry then can water when is about to get dry and in humid conditions,It is a good idea to water the Phal after the media is completely dry.

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    Just below this thread are links to similar threads on sphagnum moss. I spent some time reading through them. There was a lot of good information. As others say it does depend on your conditions as well as the type of pot you use. My conditions are cool for most of the year and not that humid. When I had phals in only moss they stayed wet for weeks if they were in plastic pots and they lost most of their roots. If they are in bark only I can never water enough. They start to look dehydrated.

    I now use a mixture of bark and moss, (more bark than moss) and most of them are in unglazed clay pots. A few new ones that I repotted in plastic pots because I ran out of clay ones are in the same mixture but I added perlite to keep the moss light. This may not work for your environment.

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    Yes as I get to see results on my orchids I have found for my environment a mix of orchiata, moss and perlite and even sometimes charcoal or LECA ?? beads has given better results. It's a guessing game on exactly when to water. I like to water but but I am trying to water only when I see the mix dry. Some grow indoors (low humidity) some in greenhouse ( very humid). So, there is a bit if trickery.

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    Yes, watering is tricky. I just acquired some oncidium types for the first time. I have no idea how to water them. They make me nervous.

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    There is no universal "one is better than another", here.

    When plant roots grow, the cells "tailor" themselves on a microscopic, cellular basis to be optimal for functioning in that environment. However, once grown, they cannot change. That means that you CAN grow any orchid in any medium (even none at all), BUT, that medium selection must "play well" with your growing conditions and personal habits (do you like to "mess with" your plants, and water often, or are you a more distant caretaker?) to meet the needs of the plant. You can't just go swapping them from one medium to another, as they will need to grow a whole new set of roots when you do.

    The trick is to think carefully about the plant's needs, your growing conditions, and personal habits, and find a medium that works well for the combination. Then do the same with the next plant - the medium may be different. Eventually, you will end up with a wide range of media, but that will make the plants easier to care for, which (of course, but don't tell my wife) means you can take care of even more plants!

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    Quote Originally Posted by raybark View Post
    When plant roots grow, the cells "tailor" themselves on a microscopic, cellular basis to be optimal for functioning in that environment. However, once grown, they cannot change. That means that you CAN grow any orchid in any medium (even none at all), BUT, that medium selection must "play well" with your growing conditions and personal habits (do you like to "mess with" your plants, and water often, or are you a more distant caretaker?) to meet the needs of the plant. You can't just go swapping them from one medium to another, as they will need to grow a whole new set of roots when you do.
    I would question this a bit. The function of an epiphytic root is to rapidly absorb water when available then prevent loss of water when not available. This wouldn't have anything to do with the media I would think but to the consistent availability of water. Wouldn't it? I have observed my phals improve rapidly when changed into a media that retains more water than not. This can't be due to new roots which take much longer to grow.

    One of my fields of study has been microbiology which leads me to be concerned more about the microbes that populate the root system than the media used to repot the plant. Soil plants have specific microbes (bacteria, fungi and protozoa) that live in the root zone or on the root that provide the root with nutrients by breaking down food sources that would otherwise be unavailable to the plant. They are also suspected of protecting the root from pathogenic bacteria and possibly even viruses. I would assume that epiphytes would have similar symbiotic relationships with microbes that colonize the roots.

    I question the practice when repotting, not so much of changing the type of media, but of washing the roots completely and in some cases drenching them with hydrogen peroxide or dilute alcohol to kill off bacteria or other pests. This would also kill off the good, helpful, and possibly necessary root bacteria. Then, the orchid is repotted in virtually sterile media resulting in a root zone that will require a long time to re-establish the root microbiome if it is able to at all. We may decide that it's the roots that need to adapt or can't adapt after repotting but it may be more of a case of re-establishing root microbes.

    I have experimented in my vegetable garden leaving the spent vegetable plants in the soil for the winter instead of cleaning them all out in the fall, tearing out the viable roots and the attached soil along with the microbes. By spring, the roots have decomposed and I hope that the root microbes are in existence to support the new crop. I have seen my garden improve every year since I started this practice. Of course, I add compost and goat manure so that may add to the improvement but it is also a good excuse for doing less work in the fall.

    When I repot an orchid I may quickly swish the roots in water but I do not sterilize them with alcohol or peroxide and I leave any bark from the old media that is attached to roots. I hope that by leaving a bit of the old media the root zone will be more quickly repopulated by essential root zone microbes. This may be more essential to the adaptation of the root than the cell anatomy of the root itself.

    I am experimenting with about half of my phals with this in mind. I put half into clay pots with a mixed variety of media that will keep them airy as well as retain moisture. My plan is to keep them in their clay pots for at least two years maybe longer without disturbing them. I plan to flush them with rain water periodically. I want to see if there is a difference between them and the ones in plastic pots that get repotted every year.

    Just about everything in my house is an experiment.

    ---------- Post Merged at 10:16 AM ----------

    And it appears to be the case. Microbes on the roots produce auxins and cytokinins:

    [Auxin production by bacteria associated with orchid roots].
    [Article in Russian]
    Tsavkelova EA, Cherdyntseva TA, Netrusov AI.
    Abstract
    Bacteria associated with the roots of greenhouse tropical orchids were shown to produce indole-3-acetic acid (IAA) and to excrete it into the culture liquid. The presence and activity of IAA were demonstrated colorimetrically, by thin-layer chromatography, and by biotests. The associated bacteria varied in their ability to excrete indole compounds (1-28 microg/ml nutrient broth). Addition of tryptophan to the growth medium enhanced phytohormone production. Upon addition of 200 microg/ml tryptophan, the bacteria isolated from Dendrobium moschatum roots (Sphingomonas sp. 18, Microbacterium sp. 23, Mycobacterium sp. 1, Bacillus sp. 3, and Rhizobium sp. 5) produced 50.2, 53.1, 92.9, 37.6, and 60.4 microg IAA/ml respectively, while the bacteria isolated from Acampe papillosa roots (Sphingomonas sp. 42, Rhodococcus sp. 37, Cellulomonas sp. 23, Pseudomonas sp. 24, and Micrococcus luteus) produced 69.4, 49.6, 53.9, 31.0, and 39.2 microg IAA/ml. Auxin production depended on cultivation conditions and on the growth phase of the bacterial cultures. Treatment of kidney bean cuttings with bacterial culture liquid promoted formation of a "root brush" with location height 7.4- to 13.4-fold greater than the one in the control samples. The ability of IAA-producing associated bacteria to act as stimulants of the host plant root development is discussed.


    Crit Rev Microbiol. 1995;21(1):1-18.
    Synthesis of phytohormones by plant-associated bacteria.
    Costacurta A1, Vanderleyden J.
    Author information
    Abstract
    The plant hormones, auxins and cytokinins, are involved in several stages of plant growth and development such as cell elongation, cell division, tissue differentiation, and apical dominance. The biosynthesis and the underlying mechanism of auxins and cytokinins action are subjects of intense investigation. Not only plants but also microorganisms can synthesize auxins and cytokinins. The role of phytohormone biosynthesis by microorganisms is not fully elucidated: in several cases of pathogenic fungi and bacteria these compounds are involved in pathogenesis on plants; auxin and cytokinin production may also be involved in root growth stimulation by beneficial bacteria and associative symbiosis. The genetic mechanism of auxin biosynthesis and regulation by Pseudomonas, Agrobacterium, Rhizobium, Bradyrhizobium, and Azospirillum, are well studied; in these bacteria several physiological effects have been correlated to the bacterial phytohormones biosynthesis. The pathogenic bacteria Pseudomonas and Agrobacterium produce indole-3-acetic acid via the indole-3-acetamide pathway, for which the genes are plasmid borne. However, they do possess also the indole-3-pyruvic acid pathway, which is chromosomally encoded. In addition, they have genes that can conjugate free auxins or hydrolyze conjugated forms of auxins and cytokinins. In Agrobacterium there are also several genes, located near the auxin and cytokinin biosynthetic genes, that are involved in the regulation of auxins and cytokinins sensibility of the transformed plant tissue. Symbiotic bacteria Rhizobium and Bradyrhizobium synthesize indole-3-acetic acid via indole-3-pyruvic acid; also the genetic determinants for the indole-3-acetamide pathway have been detected, but their activity has not been demonstrated. In the plant growth-promoting bacterium Azospirillum, as in Agrobacterium and Pseudomonas, both the indole-3-pyruvic acid and the indole-3-acetamide pathways are present, although in Azospirillum the indole-3-pyruvic acid pathway is of major significance. In addition, biochemical evidence for a tryptophan-independent indole-3-acetic acid pathway in Azospirillum has been presented.

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    Quote Originally Posted by sciencegal View Post
    <snip>The function of an epiphytic root is to rapidly absorb water when available then prevent loss of water when not available. This wouldn't have anything to do with the media I would think but to the consistent availability of water. Wouldn't it?<snip>
    But don't you think that the selection of medium would affect the consistency of water availability?

    I'm sure the "tailoring" is broader-spectrum than that, but that's a major part of it!

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    The anatomy of the epiphyte root is not going to change based on the media. That is set in the genetics of the plant which took millions of years of adaptation to its specific environment. The root has requirements. We have to adapt to the requirements of the root. It won't adapt to us. If the roots have been damaged due to our poor cultivation techniques the plant will grow new roots to replace them but those roots will have exactly the same structure as the old ones. They can't adapt to the environment we provide if it isn't right for them.

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