Use a greenhouse to keep plants through the winter months

The weather is clearly changing as we have nighttime lows down in the 40’s and the tree leaves are starting to color and get ready for their autumn dance to earth. You can smell the cooler fall weather and the weathermen are talking about wind chill temperatures again. The first frost and then the first freeze normally arrive in the next two or three weeks on the calendar. Now is the time to start planning on any tropicals or annual plants you want to save and bring inside for the winter. Some plants may be too large to save but you may want to take some stem cuttings to root and carry over to next spring. Most tropicals need to be kept near windows in good light if you are going to try to overwinter them in the house.

Many people look at the killing fall freeze as the end of a special season or memory and a chance for a fresh start or clean palette to start their garden anew next spring. Others can’t bear to lose their beloved plants, large porch or patio gardens or special plant collections. You can save a few plants in your house but space, limited light and family relations often limit the amount of plants you can bring in the house and make a hobby greenhouse the best option. A hobby greenhouse can also be a lot of fun to produce your own vegetables through the winter, to grow your own seeds and cuttings, to start your own transplants for next spring or to start your own collection of orchids, begonias, bonsai or the special plants of your choice. 

You can buy a kit greenhouse at local stores or over the internet or you can build your own greenhouse frame and cover it with a number of good greenhouse skins or glazings.  Decent kit greenhouses start at around one thousand dollars and go to as high as twenty thousand dollars for houses in the 60 to 180 square feet range depending on the strength of the frame and type of glazing. Most of the inexpensive kits are made of light weight galvanized metal or polycarbonate extrusions and are covered with either plastic film or single wall polycarbonate panels. The frames go up in cost as the metal frame gets heavier, you switch to aluminum frames or painted frames. There are a few kits that use redwood or cedar wood as the frame but over 85% of the kits sold use metal frames which probably offer the best value of strength for the money.

The earliest greenhouses were glazed with panes of glass and glass is still available but not used as often because of glazing cost and the fact that it takes more structure to support the glass. Glass is available in 1/8” thick tempered glass and in energy saving insulated glass panels. The most popular glazings these days are single wall corrugated clear polycarbonate panels or the energy saving twinwall polycarbonate in 6 or 8 millimeter thick panels. Some kits still use corrugated fiberglass and some newer kits use the more expensive corrugated or twinwall acrylic panels that will stay clear much longer.  The greenhouse grade ultraviolet resistant polycarbonate panels probably offer the most strength, durability and light transmission for the money. The twinwall panels save almost 30 to 35% in energy. Greenhouse copolymer plastic film with either one or four year life based on UV resistance is the least expensive glazing. When you install two layers and blow air between the layers as you see on many commercial quonset or barrel roof structures greenhouse plastic film is one of the most energy efficient choices. If you build your own wood or metal frame or convert a garage, shop or other building you can buy good greenhouse glazing to put on your frame. You can use 4’ wide corrugated polycarbonate panels that install by overlapping the panels and screwing to the frame. The twinwall panels that look like a sheet of square soda straws in a row install with “U” extrusions to cap the ends and sides of the 4’ or 6’ wide panels and “H” extrusions to go between the panels.

You will also need heat in your greenhouse and a unit heater is usually the best choice. Natural gas, if available, is generally the cheapest commercial fuel, followed by propane. Electric heat is the cheapest to install but costs the most to operate. Even if you are only using the greenhouse for the fall, winter and spring you will need some ventilation as all greenhouse owners very quickly appreciate the power of solar energy. You can provide winter cooling with side and roof vents or with a motorized shutter on one end and an exhaust fan on the opposite end. It is usually best to automate the ventilation on a thermostat as we often need some cooling near the middle of the day even in the winter.  It is not unusual to have the fan come on to ventilate on a 40 or 45 degree day if it is clear and sunny outside as it is possible for the greenhouse temperature to rise to over 100 degrees with solar radiation if you are not ventilating. Next summer you will probably need to add shade cloth and an evaporative cooler if you want to use the greenhouse through the summer months.

Although you can buy hobby greenhouses from mail-order catalogs or over the internet I would encourage you to buy this specialized equipment locally for the best advice on frames, glazing materials, sizing heating and cooling equipment and shade percentages for this area. There are several good suppliers in both Oklahoma City and Tulsa that would be familiar with our conditions to help you select the right hobby greenhouse for your application and crops.

Now is the time to be planting your pansies, viola, ornamental kale and cabbage and selecting and planting your spring flowering bulbs like Tulips, Crocus and Daffodils. This is also a great time to mulch your more tender hardy plants to help insulate their roots and protect them for the winter ahead.

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