Carolina Gardening: Greenhouse heat advice, please, 1 by Xeramtheum

Xeramtheum wrote:
Donna I use a box fan with a milk house heater along with 2ltr soda bottles painted black. The 2ltr soda bottles are great for sitting plants on that don't like cold feet. They collect heat in the day and release it at night .. passive solar heating. My greenhouse is about half the size of yours but how I heat mine would work with your size.

I use a box fan at one end of my greenhouse and a milk house heater at the other end along with a portable thermostat .. definitely a must and not that expensive.

http://www.kkontrols.com/poth8ftco.html

The box fan is on a timer and goes on at 7pm and turns off at 9am. Helps keep algae down and distributes the heat when it comes on. I keep the thermostat behind the heater and I have my heater set to come on at 40 degrees .. All it does is keep things from freezing and I really haven't noticed a large spike in my electric bill over the last 4 years since I've been using it.

Algae on top of the soil and spidermites will be your worst problems so keep an eagle eye out for the spidermites and try to catch them before they get out of hand .. the algae doesn't really hurt anything but looks awful and can sometimes fool you into thinking a plant doesn't need to be watered.