Keeping warm weather plants alive during winter is best accomplished with the use of a greenhouse. Although greenhouses collect and trap heat by way of their construction design, it is sometimes necessary to provide additional heat during the coldest months. It can be expensive to utilize common fuels such as natural gas, fuel oil or even wood. Applying auxiliary heat may also create humidity problems within the greenhouse. Wood stoves tend to dry things out, while gas heat may add unneeded moisture. While auxiliary heat may be necessary, you can reduce the need for it by properly orienting the greenhouse structure and applying insulation techniques.
Position the greenhouse in an east to west fashion where one full-length side is exposed to the southern sky. This will allow the winter sun to shine upon the full length of the structure. Back the north wall to an existing structure such as a house or outbuilding. This rear wall offers extra wind protection and insulation. Another option is to dig the floor of the greenhouse into the slope of a southern facing hillside. The earth, at depths at three feet or more, will remain at 55 degrees F in certain northern climates.
Use water to store heat. Paint 55-gallon water barrels black and place them inside the greenhouse to capture the sun's heat. The heat accumulated during the day will be released at night when temperatures drop.
Insulate your greenhouse. If your greenhouse is constructed of plastic, insulate with a foam sheet. These sheets can easily be placed over the structure at night and removed during the day. Also install an additional layer of plastic to the interior of the green house for added insulation. If you are constructing a glass greenhouse, use double glazed glass as the covering for the greenhouse. Insulate all end walls and the north wall with moisture proof foam insulation.
Install a large wood burning stove in the center of the greenhouse. Vent the gases through the roof using a large metal plate to dissipate the heat. This will keep plastic coverings from melting. Use large circulation fans near the roof of the greenhouse to circulate the the warm air. Create thermal storage by stacking layers of bricks or large stones around the wood stove.