Humidity levels?

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.

 

Why are you having doubts?

 

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.

 

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.

 

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.

 

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....

 

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.

 

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

 

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.

 

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.

 

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

 

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.

 

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?