Is VPD more important than light intensity for growth?

I’m trying to dial my indoor tent and having a hard time balancing everything. The more I dial up the light, the more ventilation is necessary to drop temps, which also keeps humidity around the 20-30% mark. Is it worth turning the light down to get higher humidity. I’ve left my exhaust off in veg before as experiments, and the plants seem to grow explosively when the vpd is prime.
opinions?

SmokeyBear11 said:

I’m trying to dial my indoor tent and having a hard time balancing everything. The more I dial up the light, the more ventilation is necessary to drop temps, which also keeps humidity around the 20-30% mark. Is it worth turning the light down to get higher humidity. I’ve left my exhaust off in veg before as experiments, and the plants seem to grow explosively when the vpd is prime.
opinions?

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Humidifier will bump the rh up for you. Then just dial in the exhaust so it isn't sucked out too fast.

Thank you. Is there a specific type of humidifier for grow rooms?

SmokeyBear11 said:

Thank you. Is there a specific type of humidifier for grow rooms?

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Not that I know of. I'd go with cool mist. Grab one with at a decent size tank so you need to tend to it less often with a refill.

I have one in with some seedlings, entering veg stage. Spider farmer light on 60% at 28 inches. Next week I'm dropping the light to 18 inches and blasting 100% intensity on the light.
But now I keep my exhaust on speed 2, and the humidifier in mid power. RH is 58% temp is 80.8F

You could look at something like this and DIY something (they have videos and al the parts): https://thehouseofhydro.com/index.html

That said, if you have to turn up your exhaust to combat heat which is the cause of the lowered humidity, you're going to have trouble turning the exhaust down to keep from venting the hard work your humidifier will be doing.

Depending on what your grow room setup is like, your best bet is to make sure the air being sucked into the tent is already preconditioned to where you need it.

Thanks everyone! Was having trouble thinking outside the box on this one.
happy growing!

You could just get some pet turtles like me, they're my little humidity machines.

HydroKid239 said:

Humidifier will bump the rh up for you. Then just dial in the exhaust so it isn't sucked out too fast.

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SmokeyBear11 said:

I’m trying to dial my indoor tent and having a hard time balancing everything. The more I dial up the light, the more ventilation is necessary to drop temps, which also keeps humidity around the 20-30% mark. Is it worth turning the light down to get higher humidity. I’ve left my exhaust off in veg before as experiments, and the plants seem to grow explosively when the vpd is prime.
opinions?

Click to expand...

So you want to lower VPD at the stage your plants are growing in? Are they showing signs of stress at being driven too high? I donno your style of growing, but I assume hydro. At high VPD, your plants will be sucking up the nutes a lot faster, so just lower them in response if things get out of whack. Raising the lights a bit can help.

SmokeyBear11 said:

Thank you. Is there a specific type of humidifier for grow rooms?

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Get an evaporative humidifier. It raises the humidity without spraying little water droplets everywhere. Mist style humidifiers cause moisture to build up on surfaces and can increase the chance of PM & bud rot.

I grow in soil but the natural humidity is very low where I live. The incoming air is dry, so I basically have to run my exhaust at 25% to keep my tent from being bone dry. Sounds like an evaporative humidifier for the win. Thanks for the suggestions everyone

Don’t mind it drier getting into flowering but I noticed the plants grow much better during veg when it’s a wetter environment. Better root growth and roots come to the top of the soil.
Does anyone have an answer to the title question tho... vapor pressure deficit or light intensity. Which is a bigger factor for growth and development.

SmokeyBear11 said:

I grow in soil but the natural humidity is very low where I live. The incoming air is dry, so I basically have to run my exhaust at 25% to keep my tent from being bone dry. Sounds like an evaporative humidifier for the win. Thanks for the suggestions everyone

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A lot of good diy swamp coolers out there. Good luck

SmokeyBear11 said:

Don’t mind it drier getting into flowering but I noticed the plants grow much better during veg when it’s a wetter environment. Better root growth and roots come to the top of the soil.
Does anyone have an answer to the title question tho... vapor pressure deficit or light intensity. Which is a bigger factor for growth and development.

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All environmental conditions are important, it's kind of hard to decide which is more so. It's like determining whether eating healthy or exercising is more important to be healthy, they kind of go hand in hand.

Wise answer thanks!

Been growing weed for years; I recently googled VPD because I had no clue what it even was. If you just keep temps down humidity is not much of an issue. Adding a humidifier seems to me like a good way to get moldy bud. Usually it is too much humidity that causes problems at least in my exp; especially in the summer months. Without an a/c and dehumidifier it would be intolerable in the grow areas.

Richard Drysift said:

Been growing weed for years; I recently googled VPD because I had no clue what it even was. If you just keep temps down humidity is not much of an issue. Adding a humidifier seems to me like a good way to get moldy bud. Usually it is too much humidity that causes problems at least in my exp; especially in the summer months. Without an a/c and dehumidifier it would be intolerable in the grow areas.

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I don't really get it either, humidity has always been such a problem for me due to my own local conditions. It seems like people are chasing VPD to increase their vegetative growth, which I guess matters more if you're in it for production and cutting down veg time than if you're just a hobby grower. One bad fungal outbreak and I think they would lose interest because it's almost impossible to completely sterilize a room or tent once you've covered it in spores. After a nightmare experience years ago, my #1 goal for indoor growing is to prevent fungal disease at all cost.

If you have a bunch of plants growing in an enclosed space it should be humid enough as it is. There could be something to this; seems like when you’ve got too many plants in a tight space already they outgrow it even faster. I’m always trying to slow them down; there’s only so much space in the bloom room.

Tough call but lighting has the edge IMO. Dialed in VPD with poor lighting would give you poor growth but good lighting and imperfect VPD can still result in good growth.

The difficulty I have experienced with VPD grows, flirting with mold/mildew outbreaks. From what I have read, the theory is that when the VPD is spot on your plants immunity is stronger and it's harder for mold/mildew to happen despite the temperature and RH% being favorable to an outbreak. In my experience have found this theory to be questionable as the high RH% causes botrytis or powdery mildew more often than not. I was running mold resistant genetics the few times I had success with the high RH% outside of what I will mention below). Perhaps the problems I experienced were due to the inability to stay exactly inside the tight temperature/RH% window 100% of the time or perhaps it indicates that plants don't magically become immune to PM / botrytis outbreaks. Or perhaps it indicates something entirely different lol...

A way around this would be the installation of an AirROS machine that runs 24/7. This would never let a spore live for any period of time in the room. So if we have clean plants to start with and we never let a live spore touch a plant we could perhaps run the high RH% without experiencing any outbreaks.

To that end I done one run in my testing/breeding tent that is in my veg room. The tent pulls from and exhausts to the veg room, basically a lung room. Normally I reduce my veg room RH% when I have that tent in mid/late flower. Thus far I have done one successful run with the high RH% and the AirROS machine in the veg room for several hours each day. That said I would like to see more as those genetics did not produce large colas that would be most prone to botrytis.