Humidity?

[laylow6988]

I know that humidity is important. And I am sure many of you know that as well. But what I don't know is, really what does it do to plants when stressed from humidity levels. I know you can get fungus at higher levels, and S. Mites love the lower end.


So the question...

Can the humidity level directly cause damage to the plant. I have some plants, and the bottom leaves have been falling off slowly for months now. I seem to keep it slow if I maintain a decent nute routine (Fox Farm). The humidity levels stay below 30 even with a humidifier. No less than 27.

Info: MG Organic soil. Temp range 74F-79F

 

[the widowmaker]

It all relates into the plants life cycle and what it would experience if grown in the wild.

So say you got a sativa that is native to a region closer to the equator.

That plant is going to prefer hotter climates and drier temps. Get a plant that is native to a more northern latitude and it won't like the heat so much but it will like cooler temps with some moderate rain.

For humidity though, humidity increases when water temp is higher than air temp.

When the plant is in the seedling stage, in the wild it would most likely be covered with other growth from othe plants. Its getting lower light intensity and it will be quite humid too, the other plants will act like a humidity dome plus couple that with the morning dew and its going to have fairly humid conditions.

As it grows up it gets into the air so needs less humidity.

The effects are

If you are in the younger stages then high humidity is good. Low humidity will cause thinner leaves that feel almost dry and crispy.

If you are in the flowering stages low humidity is good, and high humidity will increase your chances quite considerably for bud mold.

This could start with some grey,black or brown areas within the bud and then you get like a fibre like substance coating the inside of your bud and then it goes totally moldy.

 

[williehd1]

Very good advice Widowmaker!
The guidelines I use for southern California are:
Clones: Initially 95-100% humidity in a propagation chamber for 2-3 days, then lower humidity to 75-85% until rooted.
Vegetative: Humidity ranges from 50-70% work very well here.
Flowering: Humidity ranges from 40-50%. I haven't had any mold problems with these ranges.
I use "cool mist" humidifiers to keep from adding to the temperature increase if I need to increase the humidity.

 

[williehd1]

Oh, I almost forgot to add...
Humidity affects the plants stomata (openings) on the underside of the leaves. These stoma open and close as necessary to regulate CO2 intake. When the stoma are exposed to humidity levels above 85%, the stoma close, inhibiting further CO2 intake. Humidity levels below 45% also cause constriction of the stoma.

 

[KADE]

Lower then normal humidity levels during flowering can also cause higher resin levels.