Let’s talk Temps and RH

I grow in a wide variety of rh. Anywhere from single digit to 90%+. I used the fight it and keep it in check. However I got tired of it and stopped. When the rh is low the plants drink more. When it's high I increase airflow above and below the canopy. I do tend to get slightly higher yields and slightly faster growth rates with higher rh, nothing to get excited over. Definetly nothing worth altering my environment for, adding more work to my grow. Im not around enough to fill humidifiers and empty dehumidifiers so I dont and the difference is minimal imo

 

With auto's, the sweet spot for seedling to finish is 80'F for air, 78'F for leaf temp, and 75'F for soil temps. These are constant temps. The older a plant becomes (as it moves to transition and flower), the lower temps they will tolerate without consequences.
The real trick, is that at temps above 80'F, it can prove quite challenging to bring the RH into the zone on a VPD chart. This past winter I have experimented with running 65% RH in flower all the way down to 45% RH in flower (at the temps listed above). The higher the better, as long as the genetics have been worked well, and the strain you are growing isn't prone to PM, botrytis etc., as long as you have really good air movement. In the past, most experts have recommended the 65% RH for veg only, and dropping it down for flower. With good genetics, it isn't necessary to drop the RH. If I find a strain prone to PM, botrytis probs, I note it, let my associates know, and generally don't run it again. The other option is to maintain the lower RH, but if its genetically prone to probs, its genetically prone to probs regardless of the RH. You are just playing the margins and hoping for the best. Those of us with real good set ups can play the margins, most folks probably wouldn't want to, at least not till stuff was super dialed in and stable. The tough part of managing RH and temps is that time when lights go out, temps drop and humidity goes up. That's where the game can be won or lost. I often see tents set up, that the fans go off at exactly the same time as the lights. That can be the crux that gets ya.
For autos, the easy solution is to just run 24/0 light and give your plants a stable temp and RH all the time.
hth a little
cheers
os

 

@Organic sinse Very interesting info. I normally run 50-60 percent RH in veg and I just took my humidifier out of my room last night now that I am in flower as I was reaching 47-57 percent RH and was worried it could cause issues. This is making me want to put the humidifier back in haha. What do you think? It is staying around 45 percent with lights on and lights off it gets to mid 50's.

 

It’s all about your air movement and the genetics. Btw, the higher humidity and genetics is something I picked up fromTad Hussey, KIS Organic’s podcasts.
Cheers
Os

 

Funny you mention that I was just listening to this today

 

There is some good info there, as well as most of the KIS podcasts. I like the bug lady.
Cheers
Os

 

Far more in that podcast episode than I can offer. But I'll add that I stick to the Fluence VPD chart. In one 4x8 space I'm working in right now, the two LED's heat it up to 81-83F (easily) when lights are both on, and not dimmed. It's somewhat difficult – and not at all efficient – to maintain cooler temps in that area, without diminishing light intensity, so I just try to keep RH ~70%. At lights off I drop it to 60%. I haven't had any temp/humidity related issues.

For my own comfort working in the area I'd prefer ~77F and 60%RH. But I'll survive. It's a far cry from when I first started and was told to always run 55%RH in veg and 45% in flower, regardless of temperature.

 

We all make due with what we have to work with, 81-83'F is still really good, just think if you were running HID lighting what a cooker it would be in there,
cheers
os