Over-wintering My Cacti and Other Succulents
I over winter the bulk of my cacti and other succulent collection in two 5 x 8 ft. (1.5 x 2.5 meter) wooden boxes (shown below) that are covered with 6 mil plastic and heated with a 1200 watt electric heater. This over wintering method provides two desireable features. First, much like a greenhouse, it provides excellent winter light for the plants. Second, it allows a relatively low night temperature, usually around 42 degrees F. (5.5 degrees C). I've found that many succulents flower better when given a cool night temperature over the winter. Basically, this is a low cost alternative to a greenhouse.
The frames are covered initially with a single layer of 6 mil clear plastic. When night temperatures begin to drop below 20 degrees F. (-6.5 degrees C), a second layer of plastic is added. The plastic is draped completely over the frames and held in place with six cinder blocks per frame.
The frames have proven successful in tempertures as low as 5 degrees below zero F. (-21 degrees C), and in snowfall depths of 25 inches (63 cm). There are two major problems with this system of over-wintering. First, a loss of electricity can drop the temperature in the frames to a plant damaging level within 4 hours. To handle such an emergency I have two backup generators that can be used to keep the frames heated until the power is restored. The second major problems is very limited access to the plants over the winter. I do not remove the plastic unless the outside temperature is above 45 degrees F. (7.2 degrees C). Occasionally two weeks can pass without being able to open the frames.
I have been using these over-wintering frames for the past 12 years and they have performed well. They cost less than $300 dollars to build (the biggest expense is thermostats for the heaters) and the monthly electricity cost average about $40 for both frames.