Heat Source(s) for Mini-Greenhouses

Q.  In your answer on ‘extending your growing season’ you mention using a small heat source for the ‘mini greenhouses’. What heat source would you recommand and how is the best way to use it?

A.  Depending on the size of your Mini-Greenhouse and the severity of your frosts, you may be able to keep your plants from freezing by the use of a couple of lightbulbs placeda little distance from the ends.  Or it may require a 1500 watt electric heater, generally turned to low heat.  You will need to be careful that you don’t cook your plants or melt the plastic.  And always turn it off/unplug it when the outside temperature rises.