Viracocha711 said:
OK, I did not say to below 60f, I said below 70F...However, I do know that nute sol holds more oxygen at lower temps and temps below 70f will help control humidity thus helping to prevent mold within the res.
The best temps for a nute uptake is 60-75f, however, temps above 75temps invite mold and above 85f and there will be little oxygen in the nute sol for the plant to use and the roots are easily damaged or prone to rot and fungus...And below 50f the plant will stop growing...So, I try and maintain 65f with my frozen bottles of water, and I have had no problems yet as far as mold or root rot. My plants are growing faster than I want them to grow, if that is possible?
As far as references go, lets see, p.187 of Gardening Indoors by George Van Patten; p.319 of the Marijuana Horticulture The indoor/outdoor Medical Grower's Bible by Jorge Cervantes
Well, here we have a difference of references and actual experience. You've found a very valid reference and have actual experience doing what you've read. That's the perfect argument. No kidding.
In the 25+ years I've been growing with Hydroponics, I've used every method *except* DWC and used Ed Rosenthal's experience and advice to stay at 72 degrees and had equal results with never having any mold and have had fast growth.
"Low temperatures, however, slow down the rate of plant metabolism. Cold floors can lower the temperature in containers, thereby lowering root temperature and slowing germination and plant growth. Ideally, the medium temperature should be 70 degrees.
When watering, tepid water should be used. Cultivators using systems that recirculate water can heat the water with a fish tank heater and thermostat. If the air is cool, 45-60 degrees, the water can be heated to 90 degrees. If the air is warm, over 60 degrees, a 70 degree water temperature is sufficient."
http://www.quicktrading.com/tips16.html
I've never used his method of heating the water above 75F, but I can guarantee you that he has done it successfully, or he wouldn't have allowed it to be printed.
In another source, he suggests 72F.
Root Zone Temperature (RZT) is self-explanatory - it is the temperature in the area of the roots. Marijuana thrives when its roots are kept at room temperature, about 72 degrees. When the air temperature remains at 72 degrees and the root zone is cool, which often happens when containers are placed on a cold floor, the roots do not work as efficiently as they do at a higher temperature.
http://cannabisculture.com/articles/2565.html
Of course, there are other observations that come into the discussion:
"High root zone temperatures often plague indoor growers running water culture (aero/bubbler/dwc/hydro) systems. These systems are subject to rapid heating by intense HID lighting, which increases root zone temperatures, which decreases dissolved oxygen (DO) levels. Rapid plant growth, combined with low DO levels, can cause oxygen deprivation which in turn can result in infection by opportunistic pathogens such as pythium.
The key to maximum growth is to keep the air temperature at 75-80F, but the root zone at 68F or less. Note: the reservoir should be kept slightly cooler than the rootzone - irrigation and system heating will warm the water by the time it reaches the roots.
Optimum root growth occurs at 70-75F; however, destructive root diseases also grow and reproduce rapidly at these root temperatures. Maintaining nutrient temperatures at or under 68F maximizes root growth and DO, and inhibits pythium."
http://marijuana-ro.com/cms/index.php?page=how-can-i-keep-my-reservoir-cool
In my entire experience of 25+ years in hydroponics, I've never had any problem with keeping a reservoir temp of 75F. I'm certainly not saying it couldn't happen, and the increased oxygen in a DWC system would be extremely beneficial. In an ebb and flow system, oxygen isn't a concern. The actions involved with the recirculation processes of an ebb and flow system eliminate any possibility of that occurring.
DWC has become a very popular system to use and is highly dependant on oxygen content in the rootzone/reservoir. Saying this, in conclusion, I have to agree that keeping the reservoir/rootzone temps in a DWC system between 65-68 degrees F would be the best idea.
In the other forms of hydro, I would continue to disagree and would suggest using 72-75 F rootzone temps and using one of the many treatments that are safe to use on MJ reservoirs to eliminate the possibility of Pythium contamination as well as many others. An example of this type of treatment is "Rebound":
"Rebound kills Pythium and other pathogens in your hydroponic system. When symptoms occur, add 1 mL of Rebound per litre of water in your reservoir, and continue weekly until the symptoms clear up."
http://www.rootrotrebound.com.au/root_rot_treatment.php
As with all science, there are always differences of opinion and conflicting reports of experimentation results.
Thanks for bringing this topic up, Viracocha711. I hope you find the included comments in my rebuttal interesting.
Good luck to you, as always,
Stoney.
