Day vs Nighttime Humidity

[mopwr]

Originally Posted by Clawhammer

I am not aware of a need for higher humidity at night. Achieving high relative humidity in colder air is easier than warm air, could probably vent more at night without negatively affecting humidity. Its the stale air rather than the humidity that causes problems IMO

I think the idea of higher humidity at night being better comes from the idea that orchids leverage CAM photosynthesis. Taken from Science Direct's article on CAM photosynthesis:
"In CAM plants, stomata open at night when conditions are relatively cool and humid..."

In nature, there's always a variance between daytime and nighttime RH levels, and in some of the places these plants come from, I think they have evolved to deal with warmer / lower RH days and cooler / higher RH nights. I have heard from a few who believe matching that cycle helps growth, but everything is anecdotal.

[Clawhammer]

Originally Posted by mopwr

I think the idea of higher humidity at night being better comes from the idea that orchids leverage CAM photosynthesis. Taken from Science Direct's article on CAM photosynthesis:
"In CAM plants, stomata open at night when conditions are relatively cool and humid..."

In nature, there's always a variance between daytime and nighttime RH levels, and in some of the places these plants come from, I think they have evolved to deal with warmer / lower RH days and cooler / higher RH nights. I have heard from a few who believe matching that cycle helps growth, but everything is anecdotal.

Only some orchids are CAM, the more succulent ones like cattleya. Increasing humidity while stomata are open reduces growth (slows down transpiration) anyway, so not sure that's something you want.

RH will always go up at night if temp falls due to the fact that cold air has less potential to hold water vapor explained by Ray.