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Build a better greenhouse

Structures allow die-hard hobbyists to defy winter and nurture plants year-round

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Post-Holiday Blues are a common psychological phenomenon among the general populace, but for the gardener it is slightly different problem.

For them the malady is Post-Holiday-Lack-of-Green Syndrome. There are only two reliable treatments. One is to spend time in a warmer climate enjoying the local flora, and the other is to grow plants of your own in a greenhouse.

Depending on the seriousness of the case and the frequency of treatment, each method has advantages and disadvantages. For those who need and crave almost daily contact with plants and soil, the greenhouse might be the most obvious answer.

Since the beginning of recorded history, people have longed for fresh food and flowers out of season. To that end, we will spend a couple of weeks discussing these structures. Greenhouses are today's topic. Next week we'll talk about hotbeds and coldframes.

The earliest-known greenhouse was not built to treat a gardener for Post-Holiday-Lack-of-Green Syndrome, but it did have a medical significance. Sometime around 30 A.D., anxious servants constructed a plant-growing structure that was similar to a coldframe for the Roman Emperor Tiberius. His doctors prescribed cucumbers as a remedy for the emperor, and since there were no supermarkets with fresh produce from around the world in Rome, they had to come up with another plan.

At that time, greenhouses, as we now know them, were impossible to build because window glass had not been invented. They designed a small greenhouse called a specularium. They painstakingly fabricated it from translucent sheets of mica, a natural mineral

that occurs in certain rock outcrops.

A French botanist designed and constructed the first practical greenhouse. He built it in Holland to grow tropical plants for medicinal purposes. The idea of being inside a tropical paradise when ice and snow covered the rest of the world caught on, and soon the wealthy started building these structures for amusement and to grow exotic foods out of season.

Greenhouses became more and more elaborate as time passed. These works of art were only for the extremely wealthy. Glass was considered a luxury. It was highly taxed in many areas, so the less wealthy got their fix at the huge indoor gardens built for public exhibitions.

Perhaps the most famous was the Crystal Palace, built in London to handle the Great Exhibition of the Industry of all Nations in 1851. It had more than 14,000 exhibitors and was visited by more than six million people. Greenhouses evolved into orangeries and pineries. Pineries were not used to grow pine trees, but were made to grow pineapples. George Washington craved pineapples and ordered a greenhouse pinery built at Mount Vernon so that he could serve pineapples to his guests.

Greenhouses, by design, control the plant-growing environment. Temperature remains the most limiting factor in our area. Plants might flourish in the summer but when winter comes, most succumb to Mother Nature's chills by going dormant or dying out.

Before you decide between a plane ticket and a hammer and nails to treat the before-mentioned malady, ask yourself a few questions. Are you committed to having another hobby or avocation that is going to take considerable time and effort? While a greenhouse is not as bad as the proverbial milk cow, they do not care for themselves. Decide how much time and effort you are willing to devote to your project. Next, determine the size of your greenhouse.

Location is another major decision. Attached greenhouses offer some solar-heating benefits, but attaching a greenhouse to your home means that insects may enter your abode. Add to the insects the need to control them with occasional pesticide use, and a separate structure may be more appealing.

The structural components of the greenhouse are another important consideration. Since greenhouses by definition must let in light, the glazing or covering is critical. Make the decision based on the permanence of your greenhouse and its proximity to your home.

Cost is also a consideration, but you must make the decision based on the cost-per-years-of-service. Less expensive coverings might seem like bargains, but the need for constant replacement makes them more costly because of the recurring labor costs.

Glass was the first major type of covering, and it remains in many ways the best choice for anything connected to the home because it is permanent and durable. While it will break, it is resistant to scratching and does not lose its transparency nor turn color. Remember, building codes require tempered glass if it is used near the ground or overhead.

Many kinds of acrylic plastic are excellent for glazing greenhouses. Acrylic is expensive, but is easy for a homeowner to fabricate. It will last 10-15 years without yellowing or deterioration.

Fiberglass is popular for commercial greenhouses, but don't use it for attached greenhouses. Fiberglass is flammable if exposed to high temperatures or a flame. Use it only for freestanding greenhouses or those attached to out buildings.

Polyethylene film is the cheapest covering, but is also 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 does not suddenly disintegrate in mid-winter.

Heating, cooling, framing, ventilation and other construction decisions are important for any successful greenhouse. Decide on the purpose for your greenhouse. To start a few tomato transplants in the spring, a cold frame or hotbed may be just the answer. These will be covered next week.