Ways of Cooling Greenhouses

Windows, Vents and Fans

• Ideally, a greenhouse has windows for ventilation. You should be able to open and close the windows as you see fit. On warm but not hot days, opening a window may give the greenhouse enough ventilation to stay cool. Some gardeners use solar-powered automatic window openers. These contraptions open and shut the windows based upon the temperature when you are not home.

  Placing fans in the windows or doorway of the greenhouse is one way to get air circulating and cool the greenhouse. Gardener supply shops sell fans that come with solar panels. This is energy efficient, affordable and safe. There are no cords to run from the house to the greenhouse.

Shade Cloths

• In hot, dry climates, shade cloths prevent overheating in the greenhouse by blocking direct sunlight. Shade cloths look like black tarps and are available in garden supply shops. Shade cloths are draped on the outside of the greenhouse. They are useful and efficient; however, they must not be left on the greenhouse indefinitely. They do block both heat and light, so when using a shade cloth, remember to remove it in the morning and late afternoon so the plants inside the greenhouse get enough sunlight.

Water and Irrigation

• A water wall on the inside southern wall of the greenhouse will help maintain the greenhouse temperature. Water takes in heat during the hot day, which keeps the inside of the greenhouse cooler, and it emits the heat at night, which keeps the inside of the greenhouse warmer while it is cold outside.

  Water walls can be anything from stacked bottles of water to fancy designs with moving fountains. For a good "do it yourself" solar greenhouse water wall, stack milk crates on the southern wall inside the greenhouse. Place gallon jugs of water inside the crates. Paint the gallon jugs black or dye the water inside black. Black takes in heat better than other colors. Fix caps on tightly to prevent mosquitoes.

  Another way to use water to cool a greenhouse is to spray the inside with water. This must be done frequently to have an ongoing effect on the greenhouse temperature. An automatic misting system both irrigates and cools the greenhouse.