   Selecting a Greenhouse: Part I - February 9, 2000 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County We looked at cold frames last week. This week, we'll scale it up a notch and explore greenhouses. A low-tech greenhouse can be used to get an early start on spring planting or root cuttings. A high-tech greenhouse can be used for year-round vegetables or tropical plants. The costs of building a hobby greenhouse can vary from several hundred dollars to thousands, and operating costs can also be high if year-round heating and cooling are required. Your major decision is whether to build a greenhouse or purchase a kit. Looking at as many greenhouse styles and equipment options as possible will help you decide. Keep in mind that a greenhouse is a long-term investment. Inexpensive greenhouses have limitations such as frequent maintenance and limited season of use. Conversely, you can get anything you want in an expensive design. For most of us, our greenhouse will be somewhere between these extremes. Greenhouse kits are available for as little as $300 or up to $5,000. Shop the Internet, check the yellow pages (local suppliers are limited in our area), and watch the classified ads for used ones. Decide on the features you want first, then start compiling your information and prices. If you want to build your own, then look at several different designs, talk to others, and research it thoroughly. Yavapai County public libraries have many design resources. To help you assess your needs, ask yourself the following questions. Do you simply want to root cuttings or start seeds? If so, then a simple cold frame or hotbed may meet your needs. At most, a plastic covered, homemade greenhouse will fill the bill. Do you plan to grow tropical foliage or specialty plants? If so, then a formal, greenhouse is probably needed. If you plan to grow bromeliads, African violets, or orchids, remember that these plants have specific needs. Greenhouse styles vary widely. Appearance may be important if your greenhouse will be prominently located in your landscape. Practicality is also a consideration. A-frames are inexpensive but have little usable space. Domes are easy to build, but hard to regulate temperature. The Quonset, gothic arch, gable roof, and lean-to are the most common designs, have ample usable space, and usually complement a formal landscape. The size of the greenhouse depends on needs and space. If you think you will be serious at all, then bigger is better. Unused space may initially seem like a waste. Later, you may wonder how you did without it. 100 square feet (10' x 10') should be a minimum starting point. If you have any doubts, you can find a design that can be easily be expanded. Each type of covering material has advantages and disadvantages. Common materials are glass, polyethylene film, fiberglass reinforced panels, and double layer panels. Glass is the gold standard against which all other materials are judged. It transmits light well, is attractive with a formal appearance. Disadvantages are breakability, expense, and weight (it needs a strong frame). Polyethylene film (PE) is a good choice for home-built greenhouses. It is inexpensive and light weight. Disadvantage: needs frequent replacement. Fiberglass reinforced panels (FRPs) come in many grades and may be acrylic or polycarbonate. They are also lightweight and retain heat better than glass. FRPs are often used on Quonset style greenhouses. Double-layer structured panels (DSPs) have an open space inside them so they have added insulating properties but decreased light transmission. Next week, I will discuss location, frame materials, floors, benches, heating, venting, cooling, and other important factors for greenhouse success. Who knows, I may have already talked you out of it. The University of Arizona Cooperative Extension, Yavapai County has a new web site with horticulture information: http://ag.arizona.edu/yavapai/anr/hort/. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |