Hello to the DGC from the southern hemisphere! In my neck of the woods winter is coming and I’m battling humidity issues as the temperatures drop and my girls are a few weeks into flowering.
I’m running a 400w HPS light and due to where my tent is located I can’t run my lights during the night because I can’t control the light getting into the tent during the day so I have my dark period from 7 pm to 7 am, my problem is when the lights go off though. I’m running a 6 inch exhaust fan and dehumidifier 24/7 and venting outdoors, and when the lights are on the humidity is between 40 to 50% but when the lights go off it spikes. When I check the min / max on the humidity sensor in the morning its always up around 60 to 70%.
My question is twofold.
1) Will having humidity up around 60 to 70% mark during the dark period become an issue as the flowers bulk?
2) What other options do I have to lower the humidity when the lights are off?
On a side note, here in New Zealand we have a national referendum (reeferendum) on the legalization of recreational cannabis that is happening with our national elections in September but sadly most polls have it set to not pass at this stage. Fingers crossed we can get it over the line but I’m not getting my hopes up.
From having had the same humidity during flowering in tents before, you should be fine based upon a few things. 1- airflow, 2- defoliation and 3- genetic defenses to pm. In a perfect world, the RH would be lower, but I haven’t encountered problems with those numbers yet.
Is it possible to run a small heater fan in there during the dark period? This may help keep the air dry and the temp swings down to a minimum. Vornado is a brand of personal fans, one of which comes with heat option. The low setting is great, the CFM isn’t overbearing to the plants. I’ve tried a few desiccant type devices but they had zero effect on the overall RH.
Thanks for the reply!
I’ve got a couple of fans in the tent moving the air around and a 6 inch centrifugal fan extracting through a carbon filter so I think the airflow is ok. I’ve defoliated the bottom third but could definitely stand to thin out the canopy a bit. I’ve just been defoliating a little at a time as I don’t want to take too much and impact the flowers.
I can run a heater in the room but haven’t since I got the dehumidifier. Running a 400w HPS for 12 hours a day and all the fans and dehumidifier 24 hours a day has pretty much doubled my power bill already. But with winter coming (last night got down to 2 degrees C / 35F) I guess it’s inevitable
Sounds like you are on top of it! Have you tried keeping the humidity at around 55% during the lights on? I imagine that will help lessen the wide swing of humidity.
If the dehumidifier can be set to s specific target, that would be helpful. Granted I’m in a completely different climate, I’ve never really needed to run the dehumidifier 24 hours. Usually little corrections here and there. More so at lights off, obviously it gets higher then too. For that reason (and others), I always try to water shortly after the lights come on, let a bit of the surface water evaporate during the light cycle before sealing it up at lights off.
No humidistat on the dehumidifier but I got an inkbird humidity controller that I was going to set up tonight. Hopefully it gives me a bit more control but I’m expecting it to still run the fans all the time at night as the humidity doesn’t seem to get into the target range overnight.
I always water in the morning too and try to remove as much run off as I can, but it’s just the low temps and high humidity during the dark period that concern me.
I have also ordered a Quantum Board from Kingbrite and a small inline fan (as my current centrifugal fan sounds like a jet turbine and is massive overkill for my little tent) so hopefully the more efficient light and fan will offset the cost of running a heater at night.
Anyway to get exhaust fan on a temperature controller to avoid running during the evenings as much. That way dehumidifier can control humidity instead of constantly pulling in wet air.
I actually received a Inkbird humidity controller this morning that I was going to set up tonight but I expect because it wont drop it under the threshold it’ll just be running all night as it is currently.
I could definitely get a temp one but outside its getting to around 2c / 35f and about 10c / 50f indoors.
The air is drawn into the tent passively from inside the house and vented outside
Hi Dradd, I’d second Chad’s suggestion to add a heater fan that kicks on at night (idea being that the heater fan would impact RH similarly to running your HID lights). Also if there is a way you can dial-back the exhaust fan at night (Inkbird could maybe work for this) definitely do that (idea being lower exhaust = lower intake of high RH air during lights off). 70% humidity is a big concern to me in late flower (early flower meh I’m OK with 70%), but by itself this factor won’t cause you problems.
Yeah, last night I ran a heater and just the exhaust fan and it sat at around 55% all night. Turning on the fans inside the tent instantly started raising the humidity so I’m guessing the extra wind in the tent cools it down and spikes the humidity. The exhaust fan is way too powerful for my little tent so it’s already on a controller and throttled back to minimum power. Even cranking the exhaust fan up, with the air movement fans off still spikes the humidity.
Going to get a heater with a thermostat today to try and keep the room at a level temp over night so the humidity doesn’t spike
Powdery mildew thrives at lower temps, so I’d keep it above 75 at night, so you can sleep.