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  Wednesday, September 17, 2014  
   
 

 
Escaping Winter: Tha Magic of Greenhouses

Icy winter air has killed my treasured outdoor plants. So, in revenge, I have planned an escape. It is a cold brisk walk to the greenhouse. Opening the door, I am hit with the sweet smell of freesias and orange blossoms. Pushing aside the banana leaves, I soak in the sun and warmth. Outside may be cold, but inside the greenhouse, I live in a tropical oasis of warmth and flowers.

How can this be? This part of Virginia is zone 7, gardening lingo for a temperate climate with some really cold days in winter. While there are some plants such as camellias that are so hardy that they survive our winters outside and even bloom, most of our prized flowers and vegetables die upon the first frost. Winter becomes a time for perusing seed catalogs and planning the next year’s gardening adventure. But it does not have to be. You can save a little bit of summer under glass.

Greenhouses are magical places that soak up the sun’s energy and help us grow plants.

They come in all shapes and sizes to fit the needs of almost anyone. They can be very ornate and expensive glass conservatories or very small functional cold frames to grow a small number of plants…or everything in between.
When deciding whether to buy or build a greenhouse of whatever size, consider some of the options. Having your own greenhouse allows you the chance to grow vegetables and plants that are not commercially available at your local stores. You can also grow common food crops such as lettuce very easily and know that it is not going to make you sick or be recalled. You must decide, however, on what temperature you are going to try to maintain in the greenhouse before you select your plants. Lettuce, for example, likes cool temperatures and tropical plants like warmth. If you have a large enough greenhouse, you may be able to have a wide variety of plants with different needs. Shady corner areas or areas under tall plants will be cooler than the more open sunny spots. If you want to grow tall plants or trees, you need to consider height requirements when sizing your space.

One of the most expensive items associated with greenhouses is heating them. So growing plants that exist well just above freezing temperatures will be cheaper than growing plants with high heat requirements. If you are interested in a solar greenhouse which uses little or no heat, you should read one of the many books that have been written about them. There are a lot of details to follow in building these so they will work. Basically they use the sun to store energy produced during the day to take the bite off the drop in temperatures at night. On really cold nights or during a period when the sun does not shine, supplemental heat would be needed for these as well.

Many attempts have been made in man’s history to solve this problem of saving the heat from the sun to make plants grow in the winter. A very beautiful and ornate brick orangery was built at Kensington Palace in 1761 to try to grow oranges in the winter in Great Britain. Unfortunately, the roof was not glass and the windows on the side of the building did not emit enough heat and light for  it to work. In Virginia, we have our own early attempts to grow plants in an 18th century orangery (now in ruins) at Mount Airy in Warsaw. During this same time period, George Washington spent many hours planning and executing the design of his orangery at Mt. Vernon.

Fortunately today owning a green­house is much easier and cheaper than in earlier times. Whereas the early greenhouses or orangeries were built as masonry structures with glass windows, today we can build adequate greenhouses with less expensive materials. Instead of glass, many of our modern greenhouses use polycarbonate panels or even heavy plastic coverings over metal hoops. Although initially cheaper, plastic coverings will have to be replaced more frequently than the polycarbonate panels which should last for years. If you choose a greenhouse with polycarbonate panels, make sure they are double panels or even triple rather than single panels. The thicker panels are more expensive, but pay for themselves in energy costs when you heat your greenhouse.

The size of your greenhouse will, of course, influence the cost of a green­house. Your choice of materials will also affect the cost. If you use glass and masonry, you will spend more than if you throw some heavy plastic over metal hoops. A moderate alternative to these two extremes is buying a greenhouse kit and putting it together yourself. The manufacturer supplies the parts and you put them together. This requires someone with construction skills as the instructions with these kits are not always easy to understand and sometimes are nonexistent. Most manufacturers do provide support by phone. If you are not skilled in the construction trades, you may want to hire this one out. Some of the kits will sell you a metal foundation of sorts to anchor your greenhouse to the ground. The advantage of this is that you can move the greenhouse if you chose to do so later. If you are not going to move your greenhouse, it is better to anchor it on a concrete foundation around its perimeter. You do not need a concrete floor. A dirt floor will be fine and you can even grow things in it. If you insulate your foundation wall, you will also save energy when you heat the greenhouse and your dirt floor will stay warmer.

Whatever greenhouse option you consider, you should be careful to locate the greenhouse in an area away from trees and in an area that gets sun most of the day. The long end should ideally face south. A ventilation system is also necessary, either a mechanical one such as an exhaust fan or vents in the roof that can be manually opened and closed. Believe it or not, a closed up greenhouse on a sunny winter day can get hot enough to cook your plants. Also, the plants need fresh air and a vent for excess humidity.

If you are not ready to purchase a greenhouse, but still want to grow plants this winter, you can plant crops that like the cold such as lettuce, broccoli, cabbage, and many others in a cold frame. Cold frames are glass cases that sit on the ground so you can plant directly into the ground. They cover and protect the plant from extreme cold. Like greenhouses, they have to be vented on sunny days so too much heat doesn’t build up inside. You can buy automatic vents or do it yourself manually. Cold frames are relatively inexpensive and available from a number of gardening supply stores and online.

Not sure you want to buy a greenhouse or a cold frame? You can still grow some plants outside this winter. You will need several bales of straw. Arrange them to make your growing area. The number depends on how large you want to make it. Then take some old window frames with the glass still intact and carefully balance them on top of the bales of straw so that you have the entire growing space enclosed. This actually works very well to grow flowers and vegetables that like cooler temperatures. If it is an extremely warm winter day, slide the window frames over a little to ventilate. When the growing season is over, the straw bales will have already started to decompose. You can use them as compost for your next growing season.

While greenhouses are great for growing things, many people use their glass enclosed spaces for other activities. They can be used to enclose a swimming pool and extend the swimming season. They also make cheerful areas for winter entertaining and just relaxing in a sunny location. In these greenhouses, plants are not the primary focus, but still probably sneak in there to add their beauty. Whatever your choice of greenhouse, whatever your purpose in choosing one, you will love this heavenly escape from the doldrums of winter. Grow lovely tropical plants, your favorite flowers or vegetables, or just pull up a chair and enjoy the sun and the warmth. You will never regret the purchase of a greenhouse!

Other greenhouse options are an add-on room to your house. Many homes have glass enclosed rooms which are very plant friendly and are similar to greenhouses. The advantage to a glass enclosed room attached to your house is that you don’t have to have a separate heating system. A disadvantage would be that a greenhouse with a lot of plants has a higher humidity level than what you would want for your house.