Even with the humidifier on all the time it doesn’t get past 45%. The temp under the lights is 85F, but the leaf temp is 92F. I wanted to make better enviroment, based on the VPD chart, based for veg, but I just can’t. I would need moisture of about 75% to combat this heat. The leaves on my plants are also curled upwards (from the heat).
I have ventilation sucking the air out, but currently it is off while Iam trying to raise the moisture. If I put it on, it just lowers it further.
My lights are currently set to 400W and they are about 70cm up. The PPFD is 300. (measured with Photone app on my mobile).
I could raise the lights even higher to lower the temp, but then the PPFD would be too low, so I don’t know what to do.
So I have 3 questions:
How should I combat, to find the best balance?
At what point are the ligths too far away, so the plant doesn’t grow too big, with too much space between the nodes?
What should I do with the air exhaust? Should I just put it on when the lights are out and the room is 71F?
I have never heard of this. So you think this would actually make a difference? Right now I have a 6l cold mist humidifier, but it does nothing to the room, or very minimal. I’m going to check this out.
In the meanwhile I thought of another option I will try. I will put my exhaust to 100% to lower the temp. The humidity will also be lower, but perhaps it will be more easily managable for the plants. At least they will get constant CO2 as well, which now they do not.
I have managed to get the temp down to 75F with the exhaust on 100%. Altough some plants on the edge of the adjust a wing are still too hot. The ones directly under the light are ok.
I was wondering. Since some plants have the leaves wilted upwards from the heat, is it better to lower my PPFD (raising the light), so they will be cooler, but I sacrifice the light needed, or will they recover from the heat damage later in flowering stage and leave as is?
If running the appropriate size inline duct fan doesn’t work maybe try running your lights at night.
I have only ever had to do that while running twin 1000 watts hps. 400 watts should be manageable.
Here’s the standard I use. If plants are praying and I need more coverage, I raise the light. If they’re praying at a high angle, they’re getting too much. I had some tops yesterday with the leaves pointing almost straight up so I raised the light.
I used your approach when running a 315W CMH in a 4x4. I just keep an exhaust fan running all the time. I don’t worry about humidity most of the time. It probably affects my yield, but the plants are healthy.
you can build an enclosure for the light and vent that with a bathroom fan. i did that back in the day and it made the light cool enough that you could put your hand on the glass 2" from the bulb on a 400w hps. that’s what i would do i think. you could even isolate the fan with rubber strips from an old innertube to dampen the vibrations and keep it fairly quiet. i’ve got a design for an old reflector if you want it. you can make it with flashing and metal duct tape, not the cheap crap.
the only thing you need to watch out for is you’ll be venting using the air from inside the tent. i had mine mounted outside a box and got air from the room so it didn’t pick up the smell. yours will pick up the smell and need filtered if you need to watch that where you are.
With an enclosed fixture you can cool pretty good with a proper sized exhaust fan if you only have one light. If you have multiple lights or exposed bulbs you need sufficient AC because those temps are too high
Back in the 70s before they had all this fancy ass shit , we used to hang a towel in a dish pan of water with a fan behind it. The towel acted as a wick and put a lot of humidity in a room. To adjust the humidity just change the towel size and fan speed.
I would pull the light up a bit, but I guess you need more extraction volume in there and that’s a big area for 400w.
The damages taken will be there but as they enter flowering new leaves are born and you can disacard the ugly ones.
This is the beauty of it, you need to find your way on your space, it is true it’s weeds and they grow everywhere but in order to have good yelds and quality you need to adapt and become a better and more complete grower.
First you should solve the temperature problem, and go from there.
Howdy @M_Jake, welcome to Overgrow! With an air cooled lamp or proper exhaust and air movement a 400 watt setup should be able to dial into within a few degrees of ambient temperatures.
What is the current ambient temperature of your intake air?
It sounds like the heat from your lamp isn’t being adequately removed. Where does the exhaust go? Is it being removed fully or mixing back in with the intake air supply? If you don’t have an air cooled reflector directly at the lamps then you can basically view your entire space as the air cooled reflector that you are exhausting.
Temperature is important. The best balance will be when temps are in order. Before the plants can utilize the energy from the lamps they must first be comfortable. It would be better to have the temperature in order than the lighting intensity maxed out. You can always let the plants grow into the lights, reaching up for it as they seek more energy. It may be more ideal to keep the lamps lower by until the temperatures correspond with comfortable levels for the plants that light and it’s inherent won’t be fully utilized. Temperature is a regulator of metabolism and metabolic activity.
This depends on the genetics of the plant. An ideal situation may have the lighting from a 400 watt HID as close as 5 or 6 inches from the top of a canopy but that doesn’t mean one couldn’t have a successful harvest with lamps double or triple that distance from the canopy. Ideally have the lamps as close to the canopy as possible as long as they aren’t showing signs of stress from heat or light intensity. Too far away isn’t a specific distance, but rather a distance where the end product is unfavorable to you. Some stuff can produce full dense flowers with low levels of lighting intensity while other plants get super whispy and scraggy. It all sort of depends as these variables start to converge, temperature, relative humidities, lighting quality, and genetics.
Are you not currently exhausting 24/7? It seems like they should be happening if you’re battling high temperatures. Additionally, as mentioned by @MissinBissin, fans to help circulate and mix up the air in the gardening space can help in maintaining comfortable temperature levels.
What are the specs of the fan you’re currently using to exhaust and what is the total volume of the space you’re exhausting? What is the ambient temperature of your intake air?
Hope this is helpful for you. Many blessings and much love
The outside temperature of the intake air is 46F. When I tried to put the extraction to 100% with the lights on, the temp fell to 77F inside, and humidity was at 40%. The plant’s leaves temperature was also a little bit below 77F, though some of them still had a bit more than this. This was with the wet towels now in the room and the humidifier running.
The exahust goes out of the room and outside. There is no air cooled reflector at the lamps. Also, I didn’t put the fan to blow on the lamp, because I saw somewhere about the wind burn when the fan blows directly at the plants.
I was not exhausting 24/7 before, because I wanted to get the humidity up. But then there will be no CO2 in the room, so I’m still trying to find out the best route to take.
Now I will leave it on at all times when the lights are on (and at 10% when it is dark, because of the cold outside air).
I might put the lights still a little bit higher, to lower the temperature a bit more. The thing is, I was scared the plants will then start to grow too much and will be too tall for the room in the end stage.
It’s a lot of things to consider, so I will try to utilize what you guys told me.
So, now I know the temperature of the plant is the most important thing, and then the rest.
I have a swamp cooler routed into my mom tent. Works great. Got a tote. Cut a duct hole sealed a attachment male, connected to pipe. Then cut out square hole for computer fan to force air in. Then added ultrasonic fogger on a float system in the res. Pumps right into the tent
Don’t worry about the VPD chart, just do what you can. Those numbers are under ideal conditions with all the bells and whistles
I run a 600w MH/HPS in a 42" reflector. Lights are ~24" from the plants.
Temp can reach 85F and humidity is 40% !
But, I have two 7" fans on the floor of my enclosure (5x5) pointing up at about 30 degrees And an exhaust fan set to come on at 82F.
The idea is the circulating fans on the floor will push cooler air up to the light and when it gets too hot the exhaust fan comes on. Sensor for the exhaust fan is kept at plant top height.
As to humidity, mid winter my rh is anywhere from 20 -30%, with running the humidifier I can’t get it up much more than 50% and I simply got tired of hauling water for it !
Good news, the plants don’t seem to mind and I never have to worry about bud rot
Thank you for elaborating a bit more. It’s helpful to see this bit:
The outside temperature of the intake air is 46F.
I was wrongly assuming your ambient intake air temperature was consistently much warmer than that, and the heat was in large part due to insufficient cooling capabilities.
If possible, before plants ever go into a space it’s a good idea to run the space 24/7 with the lamps on for a while and also leave it with the lamps off for a while and record the temperatures and humidities across the day at different times. This can help dial in the most ideal timed light cycles to use if your schedule allows such customization.
Also, I didn’t put the fan to blow on the lamp, because I saw somewhere about the wind burn when the fan blows directly at the plants.
It’s advisable to have good airflow within a space with fans and such but yes you’re correct in that you don’t want the fans blowing directly onto plants very much at all. It’s good to have it blowing nearby or bouncing off a nearby wall first. I think it’s good to see the leaves on the plants gently dancing, so to speak. Soft subtle movements throughout and across the plants foliage.
For it to get 85F during lights on I’m guessing that the intake air is much warmer during the day and after the sun goes down the temps drops quickly and stay pretty low. Highland types would seem to do best in these conditions, or better performing hybrids based on redeemable qualities from highland types, so if you didn’t want to change your atmosphere you could change the genetics potential going into your space. Cannabis has shown its adaptive qualities from the equator to 40+ latitude. But also a large draw to gardening indoors is so that you can customize the atmosphere and grow something unique that you otherwise couldn’t. There is so much personal preference with indoor gardening, similarly everyone’s set of resources and resourcefulness vary. It makes each garden so unique and full of character.
A lot of helpful comments in here I’m learning a lot from this post thanks for starting this conversation @M_Jake. That’s such a beautiful garden @Chuckeye, the plants look wonderful! Hope everyone is having a great day. Many blessings and much love
, we used to hang a towel in a dish pan of water with a fan behind it. The towel acted as a wick and put a lot of humidity in a room. To adjust the humidity just change the towel size and fan speed. 
