E-mail - LED, Grow tents, humidity and temperature

Hi Doc,

I read your blog about led's and grow tents temps. I have a 39x39x79 AgroMax tent with  a 120watt Tri-BandLED. When I first set it up I was getting temps in the mid to upper 80's with very high humidity. I was afraid it would be too much for my plants so I turned on the 6" inline fan filter combo and it reduced it some but I didn't want to run it all of the time. I also have a smaller fan which is on a timer with the led and the inline fan. After that I turned down the intensity to the led and have turned off the inline fan and am now getting temps in the low 80's with about the same humidity. I also have the timer set for 18/6. What do you think? Should I go to full intensity at 24/7 or should I stay where I'm at? I don't want to damage the plants with high temps and humidity. This is my first indoor growing attempt any and all help would greatly be appreciated.

Hello again,

Thanks for the E-mail, glad to hear you are reading old posts. 
Most plants do well in the 80's.  Lower is better than high 80's but not by much.  You need to worry about heat stressing your plants when you get in the 90's and you will have problems with most plants above 100F.  Make sure you take the reading at the top of the plants, LED's do not give off as much heat as an HID, but that will still be your maximum temperatures. The humidity is most likely not going to be a problem for your plants however; you may have problems with mold if you have high humidity.  Ventilation can help with this.  A lot of people have problems with fungus when their plants start to flower or fruit develops so if you can get it down to 50% now, you will have fewer problems later.

You did not mention what medium you use, but watering the plants less can also lower humidity.  Plants need to take water from the soil and push it into the air (called transpiration) but if the medium is also evaporating water you will have higher humidity.  If you are using soil, make sure the top dries out before you water again.  You may need to experiment to find the best medium moisture for your plants with the lowest humidity.

Click here to read a post I wrote on high humidity

I hope this helps,
Good growing,
Dr. E.R. Myers