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What's a good fertilizer?

This is a discussion on What's a good fertilizer? within the General Orchid Culture forums, part of the Orchid Culture category; Amey - thank you. I appreciate you and your contributions to our community so very ...

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  1. #11
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    Amey - thank you. I appreciate you and your contributions to our community so very much.

    cheers,
    BD

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    I've been doing a lot of research on plant nutrition lately, and have learned that we have all been right AND wrong about both urea and foliar feeding - which I always regarded as a waste of time.

    According to my reading (Marschner - Mineral Nutrition in Higher Plants), more-polarized species - nitrate and ammonium ions being relatively highly so - are mostly blocked from entering leaves, but are preferentially absorbed by the roots. Less-polar species like urea however, can be absorbed directly through the leaves, but are mostly blocked from root absorption, hence the need for it to be decomposed first. You will find that fertilizer products intended to "green up" a crop, usually have urea in them for rapid leaf uptake, and WOW! do they work fast.

    Unfortunately, many epiphytes, and especially orchids, in an effort to reduce potential water loss through the leaves have developed physiologies - including thick coatings - that reduce the transfer of much of anything through the leaves. Not eliminating it, but reducing it to a fract of that seen in terrestrial plants.

    Quote Originally Posted by tucker85 View Post
    MSU fertilizers are very good because they contain more calcium and magnesium and less phosphorus but I don't know which brand has the right kind of nitrogen.
    The Greencare brand - the original stuff - uses primarily nitrate sources.

    The pure water formula is 12.5% nitrate, 0.7% ammonium. The "Well Water" formula is 13.6% nitrate, 5.7% ammonium

  3. #13
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    Quote Originally Posted by raybark View Post
    I've been doing a lot of research on plant nutrition lately, and have learned that we have all been right AND wrong about both urea and foliar feeding - which I always regarded as a waste of time.
    According to my reading (Marschner - Mineral Nutrition in Higher Plants), more-polarized species - nitrate and ammonium ions being relatively highly so - are mostly blocked from entering leaves, but are preferentially absorbed by the roots. Less-polar species like urea however, can be absorbed directly through the leaves, but are mostly blocked from root absorption, hence the need for it to be decomposed first. You will find that fertilizer products intended to "green up" a crop, usually have urea in them for rapid leaf uptake, and WOW! do they work fast.

    Unfortunately, many epiphytes, and especially orchids, in an effort to reduce potential water loss through the leaves have developed physiologies - including thick coatings - that reduce the transfer of much of anything through the leaves. Not eliminating it, but reducing it to a fract of that seen in terrestrial plants.

    The Greencare brand - the original stuff - uses primarily nitrate sources.

    The pure water formula is 12.5% nitrate, 0.7% ammonium. The "Well Water" formula is 13.6% nitrate, 5.7% ammonium
    Erm...okay, so I'm trying to process all of this...give me a minute...there's some smoke coming out of my right ear...

    Let me know if I have this straight: You're saying that urea-based nitrogen DOES get broken down in the soil...so that part is true. But it's okay to apply urea directly to foliage, because it's readily absorbed through the leaves....um, except for orchids, because they've developed thick skin to avoid moisture loss...so that basically undoes any benefit the urea could have provided in the first place?

    By the way, I don't do foliar fertilzation either...I've burned my face a few too many times with curling irons in my teens, so when I think of my poor orchids getting their leaves burned by acid, I react quite viscerally to the whole thing...I hear this sizzle in my head and...well, never mind. We'll just say it makes me uncomfortable.

    So to summarize, Urea is best for foliar fertilization, while other types of nitrogen are better for root fertilization, yes? But I know that my vandas and my paphs are getting something out of the high-urea fert I've been using, because they're growing like gangbusters.

    But my phals don't like it one bit. Burned roots all over. Hmmmm....weird. Looks like I still have a lot to learn...I will say that I'm pretty confident I'm not going to take up foliar fertilizing any time soon, so I should probably switch to the kind of fertilizer you're recommending, Ray... that Greencare brand sounds good. I'll probably still give my vandas and paphs the high-urea stuff, though, at least until I run out....just because they seem to like it so much! But one of my dendrobiums is absolutely miserable with it, and the others seem indifferent...except for my antelope den...although I think that monster could get run over by a Mack truck and come out smiling...


    Thanks for all the info! On that note, I think my brain is full...

  4. #14
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    Quote Originally Posted by OrchidAddict View Post
    Erm...okay, so I'm trying to process all of this...give me a minute...there's some smoke coming out of my right ear...

    Let me know if I have this straight: You're saying that urea-based nitrogen DOES get broken down in the soil...so that part is true. But it's okay to apply urea directly to foliage, because it's readily absorbed through the leaves....um, except for orchids, because they've developed thick skin to avoid moisture loss...so that basically undoes any benefit the urea could have provided in the first place?

    By the way, I don't do foliar fertilzation either...I've burned my face a few too many times with curling irons in my teens, so when I think of my poor orchids getting their leaves burned by acid, I react quite viscerally to the whole thing...I hear this sizzle in my head and...well, never mind. We'll just say it makes me uncomfortable.

    So to summarize, Urea is best for foliar fertilization, while other types of nitrogen are better for root fertilization, yes? But I know that my vandas and my paphs are getting something out of the high-urea fert I've been using, because they're growing like gangbusters.

    But my phals don't like it one bit. Burned roots all over. Hmmmm....weird. Looks like I still have a lot to learn...I will say that I'm pretty confident I'm not going to take up foliar fertilizing any time soon, so I should probably switch to the kind of fertilizer you're recommending, Ray... that Greencare brand sounds good. I'll probably still give my vandas and paphs the high-urea stuff, though, at least until I run out....just because they seem to like it so much! But one of my dendrobiums is absolutely miserable with it, and the others seem indifferent...except for my antelope den...although I think that monster could get run over by a Mack truck and come out smiling...


    Thanks for all the info! On that note, I think my brain is full...
    Don't try to fix something that isn't broken. If your vandas and paphs are growing well with the fertilizer that you're using, keep using it. You can't argue with success. As far as the burned roots on your phals. My guess would be that it isn't the type of fertilizer that's burning the roots but the dosage (if the damage is really fertilizer burn and not something else). Maybe you should try a less concentrated dose and water the phals before fertilizing. Good luck.

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    Quote Originally Posted by OrchidAddict View Post
    et me know if I have this straight: You're saying that urea-based nitrogen DOES get broken down in the soil...so that part is true. But it's okay to apply urea directly to foliage, because it's readily absorbed through the leaves....um, except for orchids, because they've developed thick skin to avoid moisture loss...so that basically undoes any benefit the urea could have provided in the first place?
    I think you're trying to "paint" your understanding with too broad of a brush here.

    Yes, urea needs to be broken down in order to be fully absorbed through the roots, but there is bound to be a tiny bit of absorption, even as-is. Likewise for nitrates and ammonium compounds being absorbed through the leaves – there is bound to be some absorption, but very little compared to that through the roots.

    (Let us not forget that we are not growing our plants in soil, so urea breakdown will be much slower than it would be in a terrestrial application in which the necessary microorganisms are present in large numbers.)

    As to the protective coatings on leaves, not all orchids are created equal. Phalaenopsis and bulbos, for example, tend to have less permeable coatings than do vandas, so it's not surprising that the latter might react better to exposure to urea.

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    Quote Originally Posted by raybark View Post
    I think you're trying to "paint" your understanding with too broad of a brush here.

    Yes, urea needs to be broken down in order to be fully absorbed through the roots, but there is bound to be a tiny bit of absorption, even as-is. Likewise for nitrates and ammonium compounds being absorbed through the leaves – there is bound to be some absorption, but very little compared to that through the roots.

    (Let us not forget that we are not growing our plants in soil, so urea breakdown will be much slower than it would be in a terrestrial application in which the necessary microorganisms are present in large numbers.)

    As to the protective coatings on leaves, not all orchids are created equal. Phalaenopsis and bulbos, for example, tend to have less permeable coatings than do vandas, so it's not surprising that the latter might react better to exposure to urea.
    Thanks, Ray! That makes sense! This all makes me wish I had taken a few more chemistry and botany classes in college instead of being a music education & trombone performance major. Hehee

    Although I could compose a great song about orchids, though....if anyone ever needed such a thing...

  7. #17
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    Quote Originally Posted by raybark View Post
    Unfortunately, many epiphytes, and especially orchids, in an effort to reduce potential water loss through the leaves have developed physiologies - including thick coatings - that reduce the transfer of much of anything through the leaves. Not eliminating it, but reducing it to a fract of that seen in terrestrial plants.
    Ray this is a misconception. To prevent water loss through transpiration and to prevent the escape of concentrated CO2 orchids control the opening and closing of their stomata. The cuticular wax coating are not very different from most terrestrial plants. Secondly the foliar absorption does not take place predominantly from the stomata but through transport mechanisms along the entire epidermis, which operate independently from the stomata.

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    Jenn you also might want to read this earlier discussion about foliar fertilization.

    http://www.rv-orchidworks.com/orchid...r-feeding.html

  9. #19
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    Quote Originally Posted by Halloamey View Post
    Ray this is a misconception. To prevent water loss through transpiration and to prevent the escape of concentrated CO2 orchids control the opening and closing of their stomata. The cuticular wax coating are not very different from most terrestrial plants. Secondly the foliar absorption does not take place predominantly from the stomata but through transport mechanisms along the entire epidermis, which operate independently from the stomata.
    I cannot argue with any of what you stated, but I was thinking "mechanically". Cannot the wax coatings vary in thickness or density, hence permeability? My understanding is that the wax is not a continuous "coating" as we might think of a car wax, but a series of tiny, branched, hydrophobic "rods" extending up from the surface. Any differences in their size or packing density could affect the degree of penetration of the nutrient-bearing solutions.

    Orchids have evolved in many ways in order to manage water and nutrient loss, not only by controlling the opening and closing of stomata, but by reducing the gross number of them in the first place, compared to terrestrial plants (hence the importance of good gas exchange through the roots), by primarily locating them on the underside of leaves, where they are shaded, AND in the modification of the leaf structures and coatings.

    Did I say the absorption was through the stomata? I don't think so, but if I did, it was an error. (I used to think so, but learned better.) The leaf absorption occurs through tissues called "ectodesmata" that are frequently found associated with "guard" cells that surround stomata.

  10. #20
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    Ray, the point I was trying to get across was that the mechanisms by which orchids conserve water and the mechanism by which they can absorb foliar nutrients are for the most extent independent of one another. That was the part from your earlier post that I highlighted. You are right about the cuticle not being a continuous layer. It is actually a very dynamic system similar to the lipid bilayer seen in the cell membranes. And it is variable as you mentioned, not only between different genera but it can also adapt to the environment. Plants grown under higher relative humidity seem to have thinner cuticles. I have also observed that my Phalaenopsis and Cattleyas change their foliage cuticle thickness and general foliage elasticity in response to their growth conditions. For eg. here in Germany, I grow my plants according to your perfected system of growing SH, where all the fertilization is via roots, whereas when they are transferred to India in my greenhouse they are into basket culture with foliar fertigation only. So it is a misconception that orchids can achieve only a fractional transfer of nutrients through their foliage when compared to other terrestrial plants.

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