Humidity Levels With Lights Out

[024backwards]

I have a 2x2x5' tent, in week 1 of veg, 18x6. Growing a Bruce Banner 3 in soil with SF1000W LED. My natural environment is dry, the room runs about 45%, RH/70d, so I have a humidifier that runs inside the tent. I have a 4" in-line fan drawing air out of the tent (and fresh air in). When all is balanced, I get good temp/RH readings during the day. I turn off the humidifier with the lights BUT leave the inline fan on at night to circulate fresh air. The result is a very low RH point during lights out...for example, my high RH yesterday was 68%, the low was 41% (lights out).

With all of that, my question is, should I be trying to maintain higher RH at night with lights out? I could adjust the inline fan and run the humidifier in short bursts to bring RH up, but do not want to promote mold/fungus as veg gets further along.

Thanks in advance......

 

[1ne eye]

No, i have my humidifier on the timer so it shuts off when lights out and its alot lower than 41% RH. I would say your fine. I'm about 40 RH during the day and around 24 RH when light comes on which seems ok with mine. After my plant are bigger i don't even run my humidifier RH stays around 40-45 RH.

 

[Weaselcracker]

i run my dehumidifier on a timer during lights out to keep Rh down.

You don’t need to keep the fan running during lights out. If you feel your Rh is too low just shut off the fan and the plants and damp containers should raise humidity

 

[024backwards]

thanks, it sounds like you both are ok with low RH during lights out and promote it with a de-humidifier in weasel's case. I "think" that's the core message, that I don't need to over-worry about a low RH at night. What's driving the question is really an attempt to stay within VPD temp/RH targets during veg, but that's hard to do during lights out.

 

[Weaselcracker]

In my case my outside air usually hovers close to 100% RH. With a dehum I bring it down to about 65. I’ve never had to deal with low RH so can’t say how much of a problem it is. Personally I ignore the subject of VPD, but if you think you have the means to actually do something about it, then maybe it’s worth fussing with (?) for fun, or if you’ve got extra time on your hands.

 

[024backwards]

Thanks, makes sense. I have a biology/horticulture background so am at least interested in the science of VPD. I am not sure how practical it is to implement though, so am trying to learn.

 

[Rheaun]

Like the others said the bigger plants will help maintain humidity and humdifying above 45% is risky. Consider the plant respiration during photosynthesis vs dark respiration and drybacks. I see low humidity as a way to make the plant take up what I feed it.

 

[024backwards]

Loving this thread but it can be confusing for a new grower. Its like asking everyone to advise me on which girl to ask out . Many sites/growers tell us to target RH at 55-65% during veg and only look at low RH during flower. That makes some sense as it mimics a summer/fall environment. Have you ever read Growing by Plant Empowerment (GPE)? It talks about increasing RH as temp increases and not fighting the environment to keep it cooler (in a greenhouse but I think the principal could be applied in tent that runs warmer). It is supposed to super-charge growth....It links mold issues to nute/air circulation deficiencies....And then there is all the VPD literature that suggests a similar temp/RH balance but not sure how practical it is in a fabric grow tent with a $15 hygrometer. The more I read and see folks having success with a wide variety of techniques, the more I am convinced that there are many ways to get it done with quality. The key is to make sure she gets what she needs, when she needs it, which the environment will dictate. Thanks for all the feedback............

 

[Weaselcracker]

In my grow the only humidity control that matters is keeping RH low enough in flower to avoid mould. Beyond that- RH can be whatever it wants to be.

 

[Delps8]

Thanks, makes sense. I have a biology/horticulture background so am at least interested in the science of VPD. I am not sure how practical it is to implement though, so am trying to learn.

There is discussion of VPD on various threads here. Do a search and join in the discussion. Someone with a formal background like your could provide valuable insights.

What are the concerns/questions about implementation? VPD is primarily temperature and RH. Equipment is available at the personal grow level for those individual values but I don't know of a way to control VPD directly. I use a PulseOne for temp and RH values as well as for VPD guidance (growth stage and leaf temperature are inputs). That info is used to change values on Inkbird temperature and humidity controllers. That's a manual process but it's cheap - $300 for all three sensors so it's an easy way to get started.

 

[024backwards]

Thanks Delps, I dont have a leaf temperature guage so was basing VPD on tent temperature which is way to variable to rely upon for VPD. I think if I got a laser leaf temp gauge and an accurate RH measurement, then, as I understand it, "controlling" VPD is a matter of balancing temp and RH at the canopy level based on grow cycle. I tired to do it in my current grow but am likely fooling myself into believing I am really controlling that environment. I also have implementation questions about what to do during lights out. I turn everything off accept the fan/inline fans and temp/RH swing lower. Its not a large swing, and I haven't tried to control it, but assume I would want to if strictly following VPD. My current grow is almost complete and I am going to take the summer off and start a new grow this fall so may look into this more. Are you using a laser to measure leaf temp?

 

[Delps8]

Are you using a laser to measure leaf temp?

Yes. I just aim the laser at a few leaves on each plant and come up with an average/representative number.

I think if I got a laser leaf temp gauge and an accurate RH measurement, then, as I understand it, "controlling" VPD is a matter of balancing temp and RH at the canopy level based on grow cycle. I tired to do it in my current grow but am likely fooling myself into believing I am really controlling that environment.

What brings you to think that?

I've referred to it as "influencing" the weather in the tent since I don't have an A/C unit set up but I have gotten pretty darned close to control, setting aside not keeping the humidifier filled!

Check out the pix. That's the trace from the PulseOne showing the temp, RH, and VPD for the tent over the past week. The intermittent, precipitous drops in RH are due to opening the tent or no water in the humidifier. The Inkbird controller (I refer to as "wetbird") is set to a ±2% tolerance and it controls a humidifier designed for a terrarium. The hose is used to run vapor to the back of the tent and a fan in the tent ensures that the plants are in a breeze and that the vapor mixes well.

I chose the terrarium humidifier because it's got a large, top fill tank and because it has two nozzles+hoses. You can see the hose in the res-level pix and the sensors (PulseOne, Wetbird, and Acurite) are in the center of the res, covered by a cardboard box.

The Inkbird temperature sensor ("Hotbird") is at 2º± and it's connected to an oil heater hanging in the back of the tent. Hotbird is set to 76 at the moment, but the heater only runs about an hour per day. The overnight temp drops overnight and then Hotbird switches on at 0500 and takes the temp from 67 to 75 in about 20 minutes.

Nightime VPD - there was a short discussion of this on the PulseOne forum. Peter Koverda, their tech guru, looked into the issue and, this is an interpretation not a quote, VPD is of minor significance in the overall scheme of things. If you haven't already, you want to check that site out for VPD info. In the evenings, I shut off Hotbird and I set the schedule for Wetbird to cycle a few times a night which is why the blue line (RH) drops after 11PM and then jumps up and down a bit overnight.

It's taken a bit of research to find the equipment and it's taken some time to set things up in the tent. The Birds cost about $110 for the pair, the heater was $50, the humidifier was $60, and the PulseOne is $200 so that about $420 (funny how that number came up again…) for hardware. And $60 for the Kasa smart strip that I use to control the devices, so, yeh, that knocking on $500 to "influence" RH and temp.

Per the attachment, I've been able to keep RH and temp really close to optimal. I'd expect that commercial growers work within a tighter range but what I'm seeing looks good enough for a personal grow.

 

[024backwards]

wow, ok, let me read this a few times and do some more research on some of the equipment, etc. you talked about. Thanks!

 

[Delps8]

Very welcome!