Root zone temperature

I was wondering more about “Root Zone Temperature.” What is it exactly and what would the ideal temperature be for the roots in the rockwool? And one more question: what is the ideal temperature for the reservoir in a hydroponic system?
Hydro Ho,

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.

RZT can also be used as an environmental variable in relationship to air conditions. If the air temperature is too hot, for instance 85 degrees, which is 10-13 degrees above the ideal, and the water temperature is lowered to the low 60’s using an aquarium-grade water chiller, the cool water and the warm air seem to cancel each other out. Perhaps there is a heat exchange going on within the plant.

Conversely, cool air temperatures can be ameliorated using warm RZT.

Readers with grow questions (or answers) should send them to Ed at: Ask Ed, PMB 147, 530 Divisadero St., San Francisco, California 94117, USA
You can also email Ed at [email protected], and send queries via his website at
All featured questions will be rewarded with a copy of Ed’s Marijuana Question? Ask Ed. from Quick Trading.
Sorry, Ed cannot send personal replies to your questions.