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The earliest known greenhouse was built somewhere around 30 A.D. for the Roman Emperor Tiberius. At this time, a greenhouse was extremely difficult to build because glass had not yet been invented. This small greenhouse, called a specularium, was painstakingly fabricated from small, translucent sheets of mica.
The greenhouse 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 called orangeries and pineries.
Pineries were not made to grow pine trees but were made to grow pineapple. George Washington craved pineapples and ordered a greenhouse pinery built at Mt. Vernon so that he could serve them to his guests.
Greenhouses became more and more elaborate and were, of course, only for the extremely wealthy, because glass was considered a luxury and was highly taxed. Greenhouses are now available in all price ranges and sizes and are no longer only for the wealthy.
The cold, dreary winter creates a desire to be surrounded by beautiful plants. I wouldn't mind being in a tropical paradise enjoying myself. Since I do not own a tropical island, I content myself with the next best thing - a greenhouse.
The biggest difference between a greenhouse and tropical paradise is that in paradise, Mother Nature takes care of everything. In the greenhouse, the work is the gardener's responsibility. Greenhouses are not for everyone as they require time, heat and money for successful operation.
Deciding the best construction materials, the best style and where to build it depends on many factors. Some gardeners prefer a year-round greenhouse as an extended living area of their home. Others just want a simple spot to start a few plants each spring.
Like most hobbies, greenhouses cost money, but it is often money well spent. It's cheaper than repeated tropical vacations or a psychiatrist to cure the midwinter blues.
The greenhouse location is the most important concern. Water and power are needed, as is a southern exposure. Light becomes the most limiting factor in growing most plants during the winter, so maximum exposure is important.
The first construction decision is what framing materials to use. Common choices are wood, aluminum and plastic. Occasionally, steel framing is used, but it is not recommended because it rusts so badly. Wooden greenhouses must be decay resistant, so use redwood or pressure-treated lumber. Use plated nails and other fasteners to avoid rusting. The same environment that promotes good plant growth contributes to rapid deterioration of ordinary lumber and metal fasteners.
Aluminum is an excellent framing material but is harder to fabricate, so it is generally reserved for prefabricated kits. A simple greenhouse can be fabricated using polypropylene pipe. For permanence, use ultraviolet-resistant pipe that won't become brittle in the sunlight.
Covering the greenhouse is the next construction decision. Temporary greenhouses used only for starting plants can be covered with polypropylene plastic sheeting. Do not use common construction-grade polypropylene if the cover is going to be on the greenhouse for more than a month or two, as it breaks down rapidly in the sunlight.
There is nothing quite as useless as a greenhouse with no cover in the middle of the winter. For some degree of permanence, ultraviolet-resistant plastic is highly desirable. Some brands now available last three years or more.
Fiberglass also is an excellent covering for greenhouses. It is flammable and should not be used on greenhouses attached to homes. Acrylic and double-wall acrylic plastics are also excellent if they are properly framed and constructed. Plastics expand and contract, so special glazing is needed to keep them from bulging or bowing.
Glass is a favorite material for permanent greenhouses. Building codes require shatter-resistant glass if located within 4 feet of the ground. Pre-framed glass is an excellent material for a hobby greenhouse.
By nature, all greenhouses have solar heat at least during the day. Unfortunately, the sun offers no heat at night. Storing solar heat is a worthwhile objective, but most greenhouses require additional heat at night. The simplest but most costly heating device to operate is an electric heater. Plug in and you're done because it requires no venting. All wiring must be grounded for wet locations and must be properly installed.
Gas heaters are more economical to operate but are considerably more expensive to install. They require running gas pipes and proper installation and venting by a professional. Wood, kerosene or other fuels are less useful because of the inconvenience of feeding the fires and distributing the heat.
Ventilation is a major concern because on bright days, greenhouses easily overheat and burn the plants. Automatic fans or ventilators are needed unless you want to be opening and closing doors and vents all day.
