Most gardeners dream of entering another gardening world, the world of greenhouses. Cold winds and snow are left behind upon entering a steamy, tropical paradise. Some gardeners create this paradise. If you have dreamed about building a greenhouse or currently own one and would like more tips on operating it, help is available through the USU Extension hobby greenhouse course.

The earliest known greenhouse was built somewhere around 30 A.D. for the Roman Emperor Tiberius. At this time, building a greenhouse was extremely difficult because glass had not been invented. This small greenhouse, called a specularium, was painstakingly fabricated from small, translucent sheets of mica. It was built to satisfy the emperor's craving for cucumbers out of season.The first practical greenhouse was designed by a French botanist and constructed in Holland. It was intended to grow tropical plants for medicinal purposes. As greenhouses evolved, they were known as "orangeries" and "pineries." Pineries were not made to grow pine trees but produced pineapples. George Washington craved pineapples and built a pinery at Mount Vernon so he could serve pineapples to his guests. As greenhouses became more and more elaborate, only the extremely wealthy could afford them because glass was considered a luxury and was highly taxed.

Greenhouses are built to control the environment. Temperature still remains the most limiting factor of growing plants in our area. Plants that thrived and did well outdoors during the summer must succumb to Mother Nature's chills and either go dormant or die out.

As you envision creating this tropical paradise, there are a few decisions to make. First, are you really committed to having an extra room or an extra hobby or avocation that is going to take considerable time and effort? Second, where should you locate it? Third, what should it be built of? Fourth, how will you heat it? Hopefully your concepts of growing plants and the time you are willing to devote to it are reasonable.

Once you have decided whether or not a greenhouse is for you, the next question is size. Most hobby greenhouse owners recommend making it larger than you think because your hobby soon expands to fit the available space. The next major choice is the location. Attached greenhouses offer some solar heating benefits, but the attachment also means that insects and occasionally pesticides may enter your home.

The third major decision is the type of greenhouse covering. Glass is probably the best choice for greenhouses connected to the home because of its permanence and durability. Building codes require tempered glass be used near the ground or overhead. Many kinds of acrylic are also used for covering a greenhouse. Acrylic is expensive but is easy to fabricate and will last for 10 to 15 years.

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Fiberglass is very popular for greenhouses, but it should not be used if the greenhouse is attached to a home. Fiberglass is flammable if exposed to high heat or flame and should only be used for free- standing greenhouses or those attached to outbuildings. Polyethylene film is the cheapest covering but is the least durable. It makes a good temporary covering for a simple greenhouse structure for growing in the spring. Polyethylene for greenhouse use must be ultraviolet resistant so that it doesn't suddenly disintegrate while plants are inside.

Heating is another major decision. Electricity, oil, gas or propane are available. Heating costs vary greatly according to the size of the greenhouse, but hobby greenhouse owners I have surveyed have costs ranging from $1 to $5 per day. The amount of heat loss of a given structural design can be calculated to give a good idea of what the heating costs will be. Consider your purpose for the greenhouse. If you are just using it to grow a few tomato transplants in the spring, a cold frame or hot bed may be just the answer. Alternatively, a larger, year-round greenhouse needs to be the size and shape that is convenient.

If you would like more information on building and utilizing a hobby greenhouse, we are taking reservations for our annual hobby greenhouse short course, which will run Wednesdays, Jan. 5, 12, 19 and 26, from 2 to 4:30 p.m. with a greenhouse tour Feb. 2. The $10 registration fee includes the handout materials. Pre-registration is requested. This will be the only greenhouse class this year.

Whatever your gardening interests or needs, a hobby greenhouse may be the best garden spot you will ever find. For a preview of what others have done and how to learn from their mistakes, join us the next week at the hobby greenhouse course.

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