Why is it important for plant to control the humidity?

[Maybe-123]

I'm curious about the ideal temperature needed for growing plants in a grow tent or greenhouse.
Is there an experienced grower who could share this to me?

 

[Creeperpark]

64–75°F (18–24°C) during the day is ideal however, it can be difficult to execute in Summer. Greenhouses are more useful in the cooler seasons than in the hot ones for growing cannabis.

Temperature helps trigger the stomata. The stomata allow water vapor to escape the plant via transpiration, a necessary process. Plants must open and close the stomata to maintain turgor pressure and equilibrium.

What is the simple definition of stomata?
Stomata are tiny openings or pores in plant tissue that allow for gas exchange. Stomata are typically found in plant leaves but can also be found in some stems. Specialized cells known as guard cells surround stomata and function to open and close stomatal pores. Google

 

[ganja.queen]

It depends on the cultivar. Some will grow just fine at 65F where others won't. Others may prefer up to 84F where some plants wouldn't do well at all. When you have an idea of what you want to grow it helps to look up that cultivar and see which conditions the original breeder suggests or grow journals to see other's experiences. Generally, sativas prefer a higher temp vs indica.

 

[Rocket Soul]

It also depend on lighting: leds have no IR which means you need a bit more heat.

Youre title ask for humidity but in the post you say temps,, what are you asking for really? Could be that reading up on vapour pressure deficit gives you some nice insights.

 

[Lester Beans]

Keep humidity 50% or under for flowering plants.

Temps like Creeper Park said.

 

[Rocket Soul]

Keep humidity 50% or under for flowering plants.

Temps like Creeper Park said.

Id go for higher humidity in transition phase and even mid flower, but we have good airflow. VPD works, and it generally encourages higher humidity than the old grow knowledge advice.

Though id like to hedge a bit: your growspace will not have uniform humidity, intracannopy, especially if dense and in a tent, and bottoms without good airmovement will have much higher humidity than your tops. In that case 50 may be a good advice but even better if you could manage your problematic spaces. For finishing you want low humidity for terps and cannabinoids.

This is all a bit relative to what lighting you use, with leds vpd is more important than with hids

 

[Lester Beans]

VPD is terrible for cannabis. Higher humidity mid flower?? That is exactly why weed sucks today.

They have a tent of plants at the grow store and the kid says look at this! Opens the tent, the whole while crowing about VPD, and it is nearly raining in there. Smh

It's unfortunate the methods that produce the best cannabis are now being called "old knowledge" and kids are trying to reinvent the wheel.

 

[4maggio]

Hello.. I've just reinvented myself with an LED in a 2x4 tent and controllers for Temp:Humidity:VPD
Never paid any attention or even knew about VPD.. 75F/50%.. good air flow in/out and around
always worked just fine.. VPD.. set up with the controller, things in Veg, daytime VPD is fine I can stay between the good lines. but I'm thinking that VPD must be different for night time. Before all this LED stuff night time temps were supposed to be 5-10F below daytime temps... like in nature, higher humidity. WTF are night time VPD numbers supposed to be? and with daytime temps being 83ish and higher humidity (78%ish) night time puts VPD parameters in the bad zones. I now need a heater to maintain those VPD parameters. Sorry for the ranting but I've looked for the answer to this conundrum. <Big word for small brain.

 

[Rocket Soul]

Night rime vpd is not so important, i wouldnt worry about it too much. Just make sure that its not very cold, 5-10f lower is fine. But remember with lower temps you get higher RH, which has to be controlled to avoid mold.

As a general idea: vpd is for transpiration, plant drinking, which should happen during the day. At night the priorities are no mold and not so cold that metabolism suffer; lots of the growing happens at night.

 

[mudballs]

Lower temps, lower dew point...no bueno

 

[Rocket Soul]

Lower temps, lower dew point...no bueno

Indeed. 78RH at night is too much, 4M should manage that by more extraction or a bit more heat at night, or risk mold. But the actual value of vpd is not important, he only needs to keep RH lower. If not possible then increase the air movement inside the growspace but it would still be risky to go around 80RH. Losing a crop to mold is a major sucky event

 

[mudballs]

You ever hear about spraying high or low PH adjusted water on plants? High PH is massive inhibitor of baddies growth from what i read...maybe we should push that? ...if you can't stop wet conditions, make it uninhabitable for fungal or mold to take hold.

 

[Rocket Soul]

You ever hear about spraying high or low PH adjusted water on plants? High PH is massive inhibitor of baddies growth from what i read...maybe we should push that? ...if you can't stop wet conditions, make it uninhabitable for fungal or mold to take hold.

Never heard any of that. Fight wet with... More water? Not for me.

One thing ive heard though, the milky spray. 4:1 water to milk, with a little bicarbonate. Then spray it over the leaves and make sure that it dries properly before lights off. The idea as far as i understand is that the milk inoculates the plant by feeding lactobacillus bacteria, which outcompetes mold and powdery mildew. Havent really tried it myslef so i cant swear by it just that ive heard it repeatedly online. But this is a preventive not treatment and you do it in veg.

But to me its not a very real solution, best is to manage RH by extra extraction or heating you growspace a bit. And obviously, the air you extract myst go somewhere; if you just extract to the same room the humidity doesnt have anywhere to go. If you cant extract to the outside youd need a dehumidifier for your room or you will get mold in your room as well as your plants.