Huge humidity and temp swings late in flower.

It seems no matter what I do I am screwing up. Last night I decided to run AC instead of dehumidifier. My temps dehumidifying go to the upper 80's in the night. Trichrome production looks to be less than before after a warm night.

Cut to last night, run AC temps around 68. Humidity this morning at 93%. I've seen lower 80's, but it was warm and foggy this morning.

If I don't run anything, temps will stay in the high 70's with 65% humidity at night. I have to kill my (outdoor) intake for the night.

Dehumidifier on. Temps in high 80's (87-8, RH around 35%

AC on. Temps high 60's-Low 70's RH 75%+


Is there a best scenario here. Maybe option 1. No AC/No dehumidification?

BTW I have 2 small plants in a large tent. Plenty of airflow. 1 is week 4 flowering. 1 is an auto day 90 or so.

AC & dehumidifier?
Seems RH is good with dehumidifier, temp sucks.
Temp is good with AC, RH sucks.
Have you tried both???

What are you using for a light?
And exact exhaust setup?

A pic would help others chime in, possibly.

Peace

I want to avoid running both if possible. Cost and load to an extent.

Daily I don't have an issue, just at night. My set up is.

600w HPS, 300w LED (more supplemental)

I have a 10" oscillating fan to move air in tent. I have a 4" 100cfm intake fan. A 4" 190 cfm exhaust fan w/ variable speed controller. It pulls through a 12" carbon filter at the top of my tent.

Tent is a 2.5 x 4.5 x 7.1 Sun hut grow tent. Airflow seems really good both ways. Not sure if I should kill my intake nightly or not to avoid sucking in such humid air. My tent is in a 8 x 10 free standing insulated room. I have to use my tent.

I have a hard time balancing temps and humidity also. If I let the room get cool while lights off it gets above 60% humidity. I strive to keep it below 50% or else I get PM.

I have timers set up to control my exhaust fan. If the fan runs 24 hours the room will drop to 50 degrees and hit 65% humidity while lights are off even with two heaters running ( outside its still in the 20's at night with humidity above 75% and in my shop fluctuates between 35 and 54 degrees and 54% humidity, intake pulls from the shop).

What works for me is a normal timer controlling the fan for the lights and the exhaust fan but there is a modified timer between the exhaust fan and the normal timer. Basically the normal timer is on from 8:00 am till 8:30 pm with a 30 minute off period at 2:00 pm (mid day depression). It also has a few 30 minute on periods throughout the night which allows the short cycle timer to cycle the exhaust fan on and off for 2.37 minutes at a time for 30 minutes each on period. The exhaust fan also cycles the entire time the lights are on.

It took a few days to get it working right but now the room drops to 72 degrees with a humidity no higher than 45% at lights out and 82 degrees and 35% at lights on. The only difference during the summer months is the A/C is on instead of the heaters.

You might be able to do something similar to get yours under control whether it be a timer on the a/c or dehumidifier or on your fan.

Agree with @ButchyBoy, try a timer on your dehumidifier to maintain more reasonable temps but reduce your humidity below say 50%. I'm actually trying this right now in my flower room. I put the dehumidifier on for an hour every 1 1/2 hours during lights off and it's keeping temps from 70-80F and humidity below 50%. I have an exhaust option on my dehumidifier which I'll be trying next and that should keep lights off temps below 75F I'm thinking. The worst times for me are in between seasons like right now and fall for humidity. When the AC or heat is on in the house consistently I'm fine, I tied into the HVAC and I just bring air in as needed to maintain both temps and humidity. The in-between seasons are a bitch as I'm in a cold cellar which is natively 60% humidity and I have a sump pump in there which is constantly on/off this time of year as the snow/ground thaws out.

Temps here are already out of hand. My AC dropped for a couple of hours the other day, it got to 105 really quick in my tent. My plants hate me right now, lol

What sort of air exchange are you working with? It seems like if you're hitting temps of over 105 simply because your A/C cut out that you are not extracting air. Are you growing in a garage or some sort of outbuilding? What are the ambient temps in the room the grow is located?

I think most would folks would tell you that it's not necessarily high humidity that causes issues like PM, it is large swings in temp and humidity, so you're right to be concerned. I would personally be more comfortable with reasonable temperatures and higher humidity, even in late flowering, than I would be with extremely high temperatures and low humidity assuming that you have a strain that is not prone to rot and also that you maintain enough air flow to keep things moving in the grow area. I would especially be more comfortable with the former if it was consistent, because the swings are what kill you as I mentioned.

Pretty contentious issue though, so I'm curious to hear more about your environment to see what can be done.

The temp outside was about 85. My outbuilding can get pretty hot, usually 10-12 degrees over ambient. Add a 600w hps and a 300w Platinum LED and it doesn't take much. If this was anticipated, I would have opened tent, cranked my exhaust (pulls through an air cooled hood on my HPS) and turned down to 400w from the full 600. My exhaust was only running around 60%. My tent gets great negative air pressure when battened down.

I totally agree with you or what I think you are saying. Run my AC to keep temps consistent and cooler. My humidity will stay consistent at 65% or so. I might experiment with ButchyBoy's recommendation and try using a timer. I would start with the intake only at first. When it's off it would be more passive pulling from the room. I know it's still pretty humid, but I could live with 60% or so. The plants have had a pretty good environment overall.

This morning my AC cooling the incoming humid air caused condensation to form on the inside of my tent, spiking humidity into the mid 90's.

I am in melbourne australia, i have just finished a harvest mid summer i understand those higher temps you have.
However im happy to leave my tents at around 23-30 celsius i dont find it irritates my plants too much.
As for your humidity, youll need to run a cool tube or air cooled light keep the extractor fan on 24/7 and also use an intake fan run that maybe once every 2 hours for 10 minutes.
Will sort your problems out, trying to avoid either of those things will give you heat/humidity issues there is just no escape.