It is not necessary to give up greenhouse gardening in the winter months. A clean and well-insulated greenhouse is a healthy place for winter plants, but sometimes owners must put some extra energy into keeping Jack Frost at bay. Technology offers both electric and gas-powered options for greenhouse heating; some solar greenhouse gardeners prefer to use water as a form of insulation and temperature control.
Gather and keep plastic bottles and jugs instead of recycling them through the spring and summer. Rinse them out thoroughly and keep the caps and lids.
Measure the inside of the greenhouse wall that receives the most sunlight daily. Measure the size of your jugs and determine how many jugs you need to cover this wall.
Arrange your greenhouse shelving so you can stack the jugs along this wall. You may need to purchase or build more shelving.
Fill each jug with tap water. Add a little black dye to each jug of water. Rit fabric dye works well for this; use either the powder or liquid form. Add just enough dye so that the water is black. Fix the lids on the jugs.
Stack the jugs inside the greenhouse along the sunniest wall. Try to cover the entire wall, or at least two-thirds of the way up. During the day, the water will absorb heat from sunlight. During the night, the water will release the heat it took in and help warm the greenhouse.
Run an industrial strength power cord from the home to the solar greenhouse. It is safest to purchase a new cord and inspect it well to make sure there are no cracks in the insulation.
Before winter, dig a hole next to the greenhouse running up through the base and into the greenhouse floor. Run the industrial strength cord through this hole and fill. Doing so ensures that the solar greenhouse remains insulated during the winter.
Some greenhouses may have a built-in way to run a cord into without impairing insulation.
Plug in the electric heater in greenhouse just before the first frost. Follow manufacturer's directions on how to run the heater. Use a heater specifically designed for greenhouse use. Other electric heaters will be a fire hazard in such a humid environment. For most hobby greenhouses, the smallest heaters are appropriate, but know the dimensions of your greenhouse and check with the manufacturer for the most appropriate size. Follow directions for heat settings based upon your greenhouse materials. A greenhouse made with poly sheeting will most likely require a lower heat setting than polycarbonate or glass panels.
Kerosene or Propane
Purchase a gas-powered heater from a reputable garden and greenhouse supply company.
Read manufacturer's instructions very carefully. You may need to vent the greenhouse while you run the heater. This may seem counterproductive, but a build up of fuel exhaust in the air is hazardous to your health.
Refill the gas tank as needed with appropriate fuel, either kerosene or propane.