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I have been working on a system to automate my like indoor grow tent, I have sensors to monitor the temperature and humidity. I currently have come cucumbers in there that require a high humidity and what I have noticed is that once the humidifier() is turned off the humidity drops very rapidly. I have a tent that is 38"x38"x6' and I was thinking maybe it was having a small fan that is running in there 24/7. I ran a test by turning the fan off for a few hours and it did not seem to make a difference. I have an exhaust fan attached to the end of some 8" exhaust hose(sorry for my lack of knowledge on the correct terms) but it was also turned off all day and normally only kicks on when the temperature or humidity get too high. I have also closed the vent in the back about 80% of the way. I would close it all the way but I do not have any intake venting and I worry that it is bad for the exhaust fan to run without being able to pull in any fresh air. Is this a normal occurrence or is there something I can do to help with the issue?

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  • what is the humidity inside the grow area and what is it outside the area? How are you measuring it? Is the grow area tightly sealed? – kevinsky Dec 18 '16 at 12:45
  • The grow area is air tight other than the vent in the back and the zipper wich is close to air tight but I'm sure a small amount of air can get through the zipper. I keep the humidity between 60-70 in the grow are and inside the house it is probably around 50. I am measuring with a DHT22 sensor, I also have a DHT11 in there but I recently added the 22 and found it to be more accurate. – Sean Moriarty Dec 18 '16 at 21:48
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So you are saying you have a ventilation system to pull air out of the room...do you have a way for fresh air to be pulled in passively? Fans are critical for all indoor and greenhouse plants. Do not worry, moving air has few if any negative effects for your plants. Unless the plant is being moved in the back of a truck going more than 30mph, now that is too much.

Plants USE CO2 and give off O2. The important thing is to get that O2 gas away from the leaves so that CO2 can move in to be available to the plant. As long as your room is not airtight, the air being sucked out will be replaced with fresh. Lots of growers actually use heaters for instance that give off CO2 in their greenhouses. Dry ice is another source to increase CO2 to increase plant production and vitality.

Depending on the plants you are growing, humidity is not a big deal breaker. Consistency of heat, good soil and proper light are the critical factors. Open that vent all of the way. Air circulation regulates growth and curbs fungus. If the vent is opened all the way and the temperature drops, close it down until the temperature is consistent.

Cucumbers in my experience do not do any better or worse for the humidity levels. They DO get powdery mildew with high humidity and that definitely cuts your production.

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  • Thank you for the response, I do have the vent open a bit and I have an oscillating fan that is on the plant 24/7. I am growing in a DWC hydroponic setup right now. I guess I will let it keep going and see what happens. Also, you are correct I have some 8" vent hose running out of the top of my tent with an exhaust fan at the end to pull old air out and let new air flow in through the vent on the back of the tent – Sean Moriarty Dec 18 '16 at 7:16
  • Hydroponics is NOT my area at all, grins. I wouldn't worry about the humidity level it is part of your equation already. Blowing air/air circulation is different than humidity levels. For instance stepping off the plane in Hawaii, from a crazy dry atmosphere to soft wrinkle plumping moist plumeria scented air.......ahhhhh. Keep those plants moving with the air. Selective pruning to allow more air circulation. Allow to dry out before watering. Low nitrogen in relation to P and K. Is this the first time you've tried to grow cucumbers in your tent? – stormy Dec 19 '16 at 1:56
  • Yes this is my first attempt, I believe I found the root of my problems, I replaced my water and user distilled rather than tap this time. I also re balanced the nutrients and was much more careful about measurements. This seems to have solved all my problems but thank you for the advice. It seems across the board that the advice is worry about the temp and that humidity is never going to stay steady in a room with good air flow. The guys at my local hydroponics store said the same thing as you did :) – Sean Moriarty Dec 20 '16 at 15:09
  • That is so nice to hear, Sean! Thank you. Check out my answer to my own question; how to ensure more females! And you've got to get Jorge Cervantes book The Cannabis Encyclopedia. The most detailed garden book I've ever read because it is all about ONE plant. He's able to go into light, chemistry, mechanics of automation, organics, soil and MORE. Much of the book is about indoor growing under artificial lights. Money is a big deal with this 'cash crop'!! This is producing more studies more factual information that relates to all plants. – stormy Dec 20 '16 at 21:58
  • I actually have went through and love that book, also not sure how you did but you hit the nail on the head for what this project is created for. Sadly the laws in the current state I reside in have forced me to test with cucumbers and peppers but in the future I hope to automate the growth of some cannabis. Once I can get myself into a state with medical or recreational – Sean Moriarty Dec 20 '16 at 23:26

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