# Root chilling and optimal root temperapture?



## growtek (Dec 29, 2008)

Hi all.

This is an area I've been interested in a few years.

There seems to be a root temperature range for optimal growth (73.4 - 80F for tomatoes.  Chart from U of Ohio Hydroponic Program,  last pic).   

I'm not sure what this is for MJ,  but it seems around 80f they start exhibiting signs of heat stress.

I bought a water/root thermometer and my DWC consistently runs 2-3 degrees lower than air so once I get above 82 I'm having problems.  I can vent the room more often but then I lose CO2.  

I built a rinky-dink heat exchange system.  It's passive (sits outside the room).  When the plants are older and drawing water quickly it can lower the temps (we keep our house at 67).    This passive system lowered root temps about seven degrees.   I could run higher room temps and my plants never seemed to mind. 

Did it increase yield?   I dunno, it was a great haul although I never officially measured it.  I think the buds from this grow were extreemly tight and resin filled which for me is the main goal.

TEK STUFF: This is a LONG article written in Practical Hydroponics.  It compares a variety of hydro systems and root temperatures.  Scroll to the bottom for lots of comparison pics of root mass, coloration,  growth etc.  (no pot, LOL).  

http://www.hydroponics.com.au/php/viewtopic.php?t=94


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## andy52 (Dec 29, 2008)

sounds good.i never worry about the temp of the root zone.my grow is indoors and its around 67-68 degrees in the house.the grow area is around 65 degrees.i vent from outside to cool the tent.works for me.


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## growtek (Dec 29, 2008)

Yep,  sounds like your room temps are in a range it will never be a concern for you.  In Winter it's not a  concern for me (the res is in the room now), and for most who grow in a 70-80f nothing to worry about.   

If you have a temp controlled exhaust and keep it in range you probably won't have anything to worry about.   

With 1600w vented I run 76-80F.  In Veg it's no biggie,  let the exhaust control the temp.  Once I get into flowering  I want to keep the environment closed and run Co2.   

With the chiller I had temps up to 85 with no sign of any stress.  The plants seemed to love it, but this may be wishful thinking on my part LOL.


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## POTUS (Dec 29, 2008)

growtek said:
			
		

> There seems to be a root temperature range for optimal growth (73.4 - 80F for tomatoes. Chart from U of Ohio Hydroponic Program, last pic).
> 
> I'm not sure what this is for MJ, but it seems around 80f they start exhibiting signs of heat stress.


Hey Growtek, if you keep your root temps between 70F and 75F with an ambient above ground temp of between 70F and 80F, you'll have very happy pot plants.

If you decide to heat your water for your reservoir, DO NOT heat the water directly in the root chamber.

Using "pass-though" or "bulkhead" fittings and hose, attach a second water container to your system that is of equal or more volume as your root chamber when using DWC.

Install a low volume pump that will move the water from the heated chamber to the root chamber and back again continuously.

Set your thermostat on the heater at 72 degrees and monitor the root zone temps CAREFULLY until the heater has cycled for at least 24 hours.

NEVER let the water temp rise beyond 80F or below 65F. This will result in putting your plants into a dormancy period and may also cause it to become a Hermaphrodite.

Good luck!


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## gnomegrown (Jan 19, 2009)

wow i was wondering cause i dont have a thermometer and its kinda hot in my dresser grow room


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