Greenhouse Growing in Northern Climates
Greenhouse growing in northern climates has become increasingly profitable and has been extensively used since the 1970s, when greenhouses were conventionally built of steel and glass. But with the advent of tubular frames and glazed plastic material, greenhouses became a much more effective alternative to capture and retain solar energy, heat and moisture, extending growing seasons. Visualize contemporary greenhouses as polyethylene-covered quonset huts. Does this Spark an idea?
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Expense
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When greenhouses were constructed of rigid metal frames fitted with glass panes, they were costly to build, and glass is more easily damaged from natural elements like hail, high winds and rocks. Polyethylene, on the other hand, is more pliable, cheaper and more resistant to breaking or tearing. When it does wear out or succumb to natural elements, it is much cheaper and easier to replace or fix.
Where Greenhouses Work
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Greenhouses have proven to successfully extend growing seasons in such climates as Wisconsin, Minnesota and Wyoming, to name just a few states. Greenhouse growing has even been successfully used to raise fig trees, best known for their natural acclimation in Mediterranean climates. They have even been grown commercially in greenhouses in Idaho--an unlikely climate where they have thrived. The key is to use greenhouses in climates that have extended periods of sunshine and temperatures don't drop below 27 degrees F. Below that, plants can't withstand night temperatures and will freeze.
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Cost
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The cost of greenhouses can range from hundreds to thousands of dollars depending on a number of factors. If the greenhouse is solely solar and uses a single layer of plastic, it will cost less than double-paned plastic, which increases the insulating factor due to the air layer between the sheets of polyurethane. If you want to ensure plant and vegetable growth below 27-degree nighttime temperatures, include heaters and fans to maintain growth-sustainable temperatures--which will add to the cost. It also encourages the growth of higher-profit fruits, vegetables and trees.
Size/Economics
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The size of a greenhouse can vary, and so will the cost. Crops that are particularly susceptible to frost are best grown in greenhouses. Many crops (including basil and tomatoes) are most prone to dying from early frost. Rosemary and parsley, on the other hand, are capable of over-wintering, depending on the severity of the cold and an early onset of snow that will protect them from more severe drops in temperature. If you're growing for commercial purposes, it makes economic sense to grow high-value crops such as basil that are much more expensive to buy in winter due to having to be imported from faraway climates.
Tips
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To build and maintain a quonset-hut greenhouse is relatively simple and inexpensive. Use electrical metallic conduit (EMC) for the frame. Visualize PVC piping, except rigid, and built both in straight and curved pieces. It also has straight-line couplings for width and height and "T" couplings that can be used for perpendicular strength. The conduit rods should be buried and compacted 3 to 4 feet into the ground to withstand wind, so take that into consideration when determining the height of the greenhouse. Similar to how the double-paned glass adds insulation value to windows, double-layering the polyethylene sheeting will hold in the heat and moisture more effectively. It is also more durable against the elements.
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References
- Photo Credit la serre image by harmonie57 from Fotolia.com
