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Humidity levels?

Discussion in 'Everything Else Orchid' started by MiKa, Jan 1, 2013.

  1. MiKa

    MiKa Active Member Supporting Member

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    I'm having thoughts on air humidity levels in my greenhouse. I have always considered the levels to be good for growing when they are high. But I have recently begun to have doubts that they are too high.
    The humidity is seldom below 90% (both day and night).
    I think plants would benefit from having faster dry-up rate with a lower humidity. I'm planning on installing a dehumidifier to achive a daytime drop in humidity to ~70-75%

    What is your thoughts on this?

    What humidity levels (day and night) do you have?
     
  2. Ray

    Ray Orchid Iconoclast Supporting Member

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    As far as I am concerned, and long as there is no condensation dripping on the plants, and you don't have problems with fungi, the super-elevated RH is no issue.
     
  3. keithrs

    keithrs Member

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    Why are you having doubts?
     
  4. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I have a humidity gauge, but can't remember where it is.;) But I know that 90% during the day is rare and short-lived. I think 70% is more the norm.

    My thinking is that there are some plants that do very well with high humidity, but from my research/reading the majority of what I grow doesn't experience an average of 90% in its habitat.
     
  5. MiKa

    MiKa Active Member Supporting Member

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    Marni - That is just why I'm thinking of lowering my humidity. The majority of plants just dont experience those high daytime levels in nature. I have observed that the daytime humidity levels are less than 80-85% even in the most saturated areas(except at rains) in the tropics. And most orchids grows where they get breezes with even lower levels.

    The reason I get these levels is that I need to keep the greenhouse very air tight during most of the seasons to save from energy losses and to keep it warm.

    Keithrs - I think I would definately benefit from a lower humidity at daytime. The water/nutrition turnover in the plant will increase for example. I would have less problem with algae growth on leaves. And I think that a lower level would help the plants CAM-action.
     
  6. Ray

    Ray Orchid Iconoclast Supporting Member

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    Mikael, those statements suggest that water and nutritional uptake are passive mechanisms, which to a major extent they are not. (I cannot argue with the algae, though.)

    CAM is an adaptation to reduce water loss in the daytime when the RH is naturally lower, it is not something that needs to have lower humidity. It is not driven by the humidity level? Had the plants evolved in a high-humidity environment, they probably would not have evolved into CAM plants in the first place.
     
  7. keithrs

    keithrs Member

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    I had an experience with several dial style humidity gage's where the arm going from the spring to the nettle rusted and would not allow free movement of the nettle. In my case I had 75-80% humidity all the time. When in reality I had 40-50%. If you have a dial style gage, you may want tap it to make sure the humidity gage is working.
     
  8. keithrs

    keithrs Member

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    An other thing is that most dehumidifers use a/c unit or thermo exchange to condensate the moisture and they send out cool dehumidified air. I'm not sure how this will effect your greenhouse.
     
  9. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I don't use gauges for humidity. If the air feels "buoyant" I'm good. If the air feels "heavy" or "dry" I'm not happy about it.

    It must be very difficult to have to keep a tight greenhouse for extended periods of time. I have the luxury of a climate where I can get good fresh air exchange almost any day. As well as lowering the humidity, do you have enough fans? Is there enough mixing of the layers? I run the majority of my fans under the benches and a few up high. Last summer a friend was visiting and pointed out that I wasn't getting much mixing of the air. I put two small fans on the floor and angled up at about a 45 degree angle and it made a huge difference.
     
  10. MiKa

    MiKa Active Member Supporting Member

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    I have very sophisticated humidity meters and actually run two separate to exclude errors. So I'm sure of the readings.

    Its a challenge to grow in this climate as the seasons changes climate 4 times a year. From blistering cold down to -30°C and zero light in winter, to temperatures up to +30° C and sunlight almost 24 hours a day in summer. :confused:

    Here is how it looked a couple of days ago at 2:30 pm. :rolleyes:

    afarm9.staticflickr.com_8351_8302774065_6af657fed4_b.jpg

    I run three big fans in the greenhouse to spread the heating. So there can not be more air movement.

    The dehumidifiers that are used here in Sweden work by drawing moist air over a refrigerated coil with a small fan. The cold coil of the refrigeration device condenses the water, which is removed, then the air is reheated by the hot coil. Usually there is a small surplus of heat in the process that I can benefit from.
     
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  11. keithrs

    keithrs Member

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    That must be a very difficult climate to grow in!

    The dehumidifier that you describe is basically what I was going to suggest only I was going to recommend using antifreeze and use a pump to circulate it outside to a coil then back into the house. You can thermostatically control the pump so the condention won't freeze the coils shut.

    I erased the post because you had said something about energy use.

    Sounds like you got it worked out! I have to really admire you. You have been dealt a tough hand for orchid growing. Ill be moving to Latvia in the next couple years to help my in-laws get there retirement home and greenhouses going. Can't wait....
     
  12. Alexey

    Alexey Well-Known Member Supporting Member

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    Disagree. Constantly keeping relative humidity above acceptable for the particular species level will shut down transpiration function of the plant for significantly long period of time. There is no evidence (at least I have not found) that active root uptake is efficient enough to substitute transpiration and maintain plant in health.
     
  13. Alexey

    Alexey Well-Known Member Supporting Member

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    Looks like answer is in your collection. Not so many orchid species will thrive in the environment with constantly higher than 90% relative humidity. Here is the link which can be useful. You can find 6 or 7 publications of the same author on a rootzone topic on this website.
    http://www.greenhousecanada.com/index.php?option=com_content&task=view&id=1935&Itemid=153
     
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  14. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    Mikael, my hat is off to you. I don't think I could deal with your climate.
     
  15. MiKa

    MiKa Active Member Supporting Member

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    Alexey - Thank you for the very useful links. I have read most of the parts now and it make me more convinced that my doubts was justified.

    I bought a dehumidifier yesterday and is testing it out right now.
    The problem right now is that I can not control it externally. As soon as the power is shut off, the system goes into passive mode when the power comes back. I have to think of a way to override it, so it can be controlled with a timer. If anybody has some advice, please chime in.

    A good thing is that it produces a lot of destilled water that can be recycled :)
     
  16. Ray

    Ray Orchid Iconoclast Supporting Member

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    c'mon, Marni. I think YOU have done some things, and grow some plants, I wouldn't touch.

    I must say though, that Mikael is, by far, one of the more creative orchidists out there.
     
  17. Ray

    Ray Orchid Iconoclast Supporting Member

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    A good thought, Alexey, but that assumes that transpiration is passive, doesn't it? As respiratory processes go on, there is likely water "swept along" with the gas exchange.
    I figure there is probably a balance. If there wasn't, then an orchid could grow well in an arid environment, if it had a good enough root system and it was watered enough.
     
  18. keithrs

    keithrs Member

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    What do you mean by externally? Do you want to control it from your main house or just simple timer to turn the power outlet off?

    Please expand
     
  19. Alexey

    Alexey Well-Known Member Supporting Member

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    It looks like there is only one active component: group of cells acting to close or open stomata, to regulate rate of transpiration. Molecules of water move from stomata (plant) to ambient air due to gradient of RH between these two areas. Increasing RH in growing area higher than critical point we are nullifying gradient and shutting transpiration off. There is no active exhaling component in plants. As such - one can name transpiration as passive.
     
  20. Alexey

    Alexey Well-Known Member Supporting Member

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    It would be great to know, if there is a way to overcome it electronically. For me it is easier to use old-country-stile of thinking. What if to place working dehumidifier in an enclosure (box) which has air intake and air exhaust openings with exhaust fun activated by timer?