Greenhouses can be used to extend the growing season and to just grow unique plants year-round. While we usually think of greenhouses as growing structures that increase air temperature, they can also keep plants cooler during warmer months. This is especially important in the Southeast. However, the design of a greenhouse is critical delivering desired results. It’s also important to consider installation and maintenance costs, location and orientation, covering, and air circulation.
Design
Lean-To – A lean-to greenhouse utilizes an existing structure for one or more of its sides. Advantages include being close to available electricity, water, and heat and for strength provided by being attached to another structure. Disadvantages are limited space, light, ventilation, and poor temperature control.
Quonset – The frame of a Quonset structure is circular/curved and usually constructed of electrical conduit or steel pipe. These frames are usually covered with plastic sheeting. Sidewall height is low, restricting storage space and headroom.
Gothic – The gothic frame is similar to the Quonset, but it has a point at the ridge instead of being curved. Sometimes these structures utilize wooden arches that are joined at the ridge. This design provides more headroom at the sidewalls than the Quonset.
Gable Roof – Gable roof greenhouses consist of sidewalls, end walls, and of course a gable roof. These structures generally provide the most headroom throughout and allow for more light to come through. However, more materials are required for the sidewalls and roof structure.
Location
Like a house, a greenhouse should be located on a level spot with good drainage. A greenhouse also needs full sun exposure. The south or southeast side of the house in a sunny location is the most desired spot, because it will allow the greenhouse to capture the most sunlight from November to February. The next best location is the east side, followed by the southwest and west. The north side is least preferred. Of course, if you have a lot of property, you can place it in a sunny spot. The best orientation for our part of the country is from north to south to allow for more even lighting throughout the day.
Covering
Greenhouse coverings are usually made of either glass, fiberglass, or plastic. Glass has a more insulating cover than other materials, but it can be broken easily and requires stronger framing due to weight. Fiberglass is lightweight and strong and can last a long time. However, light penetration degrades over time with lower grade fiberglass. Double-layer plastic sheets last a very long time and retain heat well. Polycarbonate products yellow faster than acrylics. Film plastic is available in many quality grades and materials. It requires a lighter structural material, because it weighs less than other coverings. Utility grade polyethylene can be used, but commercial greenhouse grade polyethylene has ultraviolet inhibitors to extend its life and to protect against ultraviolet rays.
Air Circulation, Ventilation, Heating, and Cooling
Fans, heaters, vents, and even small evaporative coolers can help with greenhouse climate control. For more information on climate control, please refer to the Hobby Greenhouses publication from the University of Georgia.
Building a greenhouse can be a big, but very rewarding endeavor. It’s important to think about all the factors to build something that works best for your situation. With some research and commitment you’ll be on your way to extending the growing season and growing your own unique plants.
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