Relitive Humidity and heat

Good afternoon. I am not using a tent. I have converted the back bedroom of my house into a grow room. I am currently growing 8 Gorilla Glue autos and each plant has its own LED 1200 watt equivalent. I have a few side lights and Mylar on the walls. I am using 5gal cloth bags, Fox Farms Potting Soil mixed with Living Earth Super Soil. I water every three days or so. I have an exhaust fan venting to the room, fresh air through the room vents, and I keep a ceiling fan running. The only thing I Am unsure of is the atmosphere inside my room. The temp runs between 85-90 degrees F. and the RH is anywhere from 21%-54%. Will foliar feeding with something like aquarium water or tap water be okay on low humidity days. Thanks for any info on this.

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Well as heat rises rh goes down. If your above 85F that’s not good for your plant. Ideal 70-85. If you lower your temp your rh will rise naturally. I don’t know about foliar feeding because my nutes aren’t recommended for that. I have a oil diffuser from Walmart that raises my rh relatively well. Also get a VPD chart and try and keep your rh in range for your stage of growth


I would not use anything other then clean water to spray the girls…
If you want to give them a little co2 boost , you can spray them with sparkling water out of a can…
Make sure that your lights aren’t so close that the plants will get burned by the water droplets… :wink:


Try to get away from the “watering every x days” and water them when they actually need it. One method is to go by the weight of the pot. It will feel significantly lighter when it is dry. The other method is to insert your finger into the soil up to the second knuckle to check the dryness. When you feel moisture only near the tip of your finger, it’s about the right time to feed the plant.

You definitely should try to reduce the temperature in your room. It’s a bit hot.
If you are unable to get a humidifier in that room, you can try hanging wet towels. They will help a bit.

Here’s a humidity chart. You don’t have to follow it verbatim, but it’s a good basic guideline.


Thank you for the chart. What does the VPD number represent?

Vapor Pressure Deficit. I’ll just paste the wording from wikipedia as I couldn’t explain it any better than this:

Vapour-pressure deficit , or VPD , is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated. Once air becomes saturated, water will condense out to form clouds, dew or films of water over leaves. It is this last instance that makes VPD important for greenhouse regulation. If a film of water forms on a plant leaf, it becomes far more susceptible to rot. On the other hand, as the VPD increases, the plant needs to draw more water from its roots.

If you meant “where does that number come from?” Well, that’s a big equation. You can see it at the wikipedia page:

If you look in the upper corner of the chart I provided, it shows the ranges for various growth stages.



I am using plastic drawers from one of those cheap plastic sets. I am using 5GAL cloth pots and they fit in nicely with several inches on all sides. If I keep an inch or so of water in the tray, and it brings up my humidity, will it hurt the plants in the long run, full time bottom watering?

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If you leave the water in it can;
Attract insects
Promote root rot
Raise your ppms because your not dumping any out.
I’ve bottom fed all the way thru plants life before. I fill it up and let it sit 30 mins then dump the water. I would, if possible, find another way to change humidity.