Humidity levels?

Alexey, that's not entirely the case, as there is literally mechanical pressure across cell membranes that forces the movement of water. Yes, there is passive loss through stomata (which is what CAM plants attempt to overcome), and no, there is no massive, muscle-driven "breathing" going on, but there is symplastic movement of water and solutes through the plasmodesmata, and apoplastic transfer through cell walls and the intercellular spaces, which actually has less resistance to the flow of water. Once that happens, usually as a result of ionic imbalances resulting from nutrient uptake and the subsequent chemical processes within the plant, it "forces" more active transfer out through the roots and the plasmodesmata, as well as passive transfer through the stomata.

 

Ray, it would be great if we could make a progress in this discussion. However, we are back at the beginning: active root uptake is driven by ionic gradient, transpiration is driven by RH gradient. Extremely high RH in growing setup is anti-productive due to suppression of transpiration.

 

If you can bypass somehow the built in thermostat setting your machine has and use it only as a machine you can use the plug above to run your dehumidifier set it with a day humidity and have it shut at night so the humidity rises

 

Alexey, I guess we'll have to agree to disagree.

Agreed.

Not entirely, and this is where we disagree. It seems to me that if the ionic gradient draws water into the plant, that process would continue until the plant exploded. So where is it going? Some of it must be driven out through the plasmodesmata by the hydrostatic pressure it causes within the cells.

I can agree in concept, but my own experience does not support that it is a real issue. My greenhouse has stayed above 90% RH for at least the last five years, and my plants are doing great.

 

The only way is to bypass or hard wire it inside the machine. I cant really give advice how to bypass it because I would have to see how it's wired inside the machine.

What brand and model is it?

If you know anyone who know electronics and wiring.... Give them a call.

 

Ray, perhaps results can go from "great" to "superb" at the lower humidity levels. Plans slow their growth and loosing their rigidity/stiffness at the extremely high RH.

 

Possibly, but I have not noticed any loss of turgidity.

 

Ray, plant turgidity reflects water metabolism, and its temporary issues can be observed at the extreme levels of RH. What I referenced, talking about rigidity/stiffness of the plant is a correlation between rate of transpiration and mechanical tissue development. Suppression of transpiration ( e.i. Due to high ambient RH) leads to permanent structural underdevelopment of new growth.
In general, my point is: if we all are aware that extremes of light intensity, temperature, watering and use of fertilizers are non beneficial for orchids, why we shall advise extremely high RH as favourable? As any other parameter of growing environment it can be harmful and has to be maintained at optimal, not extreme levels

 

I have to agree with your general assessment, Alexey. Somehow though, I just think the RH issue is less critical. Maybe not unimportant, but possibly less so.

And thank you for the exchange. In many forums, it degrades to the level of "Jane, you ignorant slut" almost instantly.

 

This thread might be dead, but it sounds like many of you know quite a good deal about the science behind orchids. I am always looking to learn so if any of you could suggest good reading on the subject, it would be great. Thanks.