A greenhouse is a good investment for avid gardeners. Greenhouses allow gardeners to extend the growing season and propagate plants year-round. Greenhouses are traditionally made from a metal, fiberglass or plastic frame with glass, vinyl or plastic windows. Plan your greenhouse carefully, considering your gardening goals, as well as your resources. A greenhouse no larger than 8 feet by 12 feet is sufficient for most home gardeners' needs. Situate the greenhouse on a level, sunny site, preferably on the south or southeast side of a building or group of trees and provide an adequate heating and ventilation system.
Determine the ideal temperature for your plants' growing needs. For example, if you are starting seeds or growing warm-season vegetables, you'll need to keep the greenhouse temperature above 75 F. If you're growing cool-season vegetables, a temperature of 55 F is sufficient.
Install a thermostat in the greenhouse to monitor temperatures. Install it at the level of the plants, shaded from the sun and away from any drafts that may affect the accuracy of the thermostat readings.
Install a 220-volt circuit electric heater in the greenhouse if you plan to use the greenhouse all winter. Run the heater when temperatures dip below the level recommended for your plants.
Place two fans at diagonally opposite corners of the greenhouse. Set the fans at least 2 feet from the greenhouse walls. Run the fans during the winter to keep warm air circulating throughout the greenhouse. Without fans, warm air will rise to the top of the greenhouse, while cold air chills the plants below, per West Virginia University Extension.
Install roof vents with side inlet vents in the greenhouse. Greenhouse kits often come with built-in vents.
Install one single-speed exhaust fan and one two-speed fan to provide additional ventilation. During the winter, one fan is probably sufficient, but run both fans during summer months to regulate temperatures.
Install an evaporative cooler (also called a swamp cooler) or shade cloth blinds to further cool the greenhouse if the fans are not enough to keep temperatures cool during the summer.