Extending Your Growing Season – Pine Bluffs Post

I spent the last three days at the Ask-a-Master Gardener booth at the Cheyenne Home and Garden Show answering questions and helping many new gardeners and a variety of seasoned gardeners from south Denver, west to Vancouver afford to. Washington and as far north as Montana. It was wonderful to see so many people interested in starting a new garden or expanding an existing one. I would also like to thank everyone who came to visit and talked. I enjoyed meeting so many readers and listeners to our radio show. Speaking to the public and listening to their experiences and views is always interesting and helps me understand what people are interested in and build my own knowledge. There were several questions from seasoned gardeners that I’ll be answering over the coming weeks, and some from new residents of Laramie County.

The most frequently asked question was about extending the growing season. It was never asked in those words, but we asked questions from several people, both new and long-term residents, about greenhouses, tire houses and elevated tunnels. All three allow you to start plants earlier and grow later in the season, but there are differences.

Greenhouses are probably the most familiar to people. Whenever you go to kindergarten, you’ll see at least one greenhouse on the property, although tall tunnels are becoming more common. As a rule, smaller plants such as bedding and houseplants are grown and kept there. Building a greenhouse is a science and an art. They will be hard sided with special glass made just for greenhouses or polycarbonate sheets. Polycarbonate has largely replaced fiberglass for roofs (and siding) because it is hail-resistant and remains flexible over time and in cold weather. A few years ago we had a route with freezing temperatures, accompanied by very strong winds. I went out to check the greenhouse and found that a piece of the polycarbonate siding had come loose and was flapping in the wind, bending up and down. With fiberglass and even steel cladding, it would have been weakened and broken off. When I found that it had never been screwed on, I felt a little better because it hadn’t come loose. I screwed it down and put a piece of Flex Seal tape on the crack and everything has been fine since then.

Greenhouses will also have the roof made of clear material. One of the main advantages of a greenhouse is the amount of natural light, which reduces electricity consumption. In most cases, additional light is not needed unless you have to work after dark. Because of the entire glass or polycarbonate, a greenhouse absorbs the sun’s rays and converts them into thermal energy. It’s the same principle that the sun heats your car on a bright, sunny day. The solar energy comes in as a short-wave energy source, but is tuned to long-wave (heat) energy as it passes through the clear material. The long-wave energy cannot come out again and becomes trapped in the structure, be it a car or a greenhouse. Without good ventilation, temperatures can rise to unacceptable levels very quickly. My greenhouse reached 142 degrees last summer and was often over 100 degrees this winter. Since I wasn’t growing anything, I wasn’t too worried. That has to change this summer when it goes back into production. Greenhouses are often artificially air-conditioned. Reifenhäuser and high tunnels are heated according to the same principle.

A tire house and an elevated tunnel are basically the same type of structure, differing only in size. A hoop house can be very small, good for starting bedding plants, or large enough to stand up. The larger version (high tunnel) can easily be 15 to 20 feet high in the middle and quite wide. Construction methods vary slightly, but the concept is the same regardless of the materials used. Both consist of sheets made of a flexible material. Most commonly, two and a half inch PVC pipe is used. The pipe is attached to the ground on one side, then bent into an arch and attached on the other side. In a tire house, most of the time the pipe is fasted right to the ground, while an elevated tunnel (but not always) has raised sides or posts made of a different material that raise the starting point of the arches. The height of the structure depends on the width and length of the pipe used for the arches. It is then covered with a plasticized film made for this purpose. There are doors at each end and a method of ventilation must be included. The most common method of ventilation is to simply roll up the pages and let the breeze cool in. This works well until the ambient temperature of the breeze is too hot to provide adequate cooling. This can easily happen later in the summer, so fans can be used to improve cooling.

Rich Lewis, master gardener, is building a modified version of an elevated tunnel that has both the characteristics of an elevated tunnel and a greenhouse. He will bury the building three feet into the ground and bury the ground around the building to provide six feet of natural insulation. Then he uses a PVC pipe that is covered with a polycarbonate sheet. I look forward to his results.

Cooling any of the structures can be a major obstacle to overcome. Because the greenhouse is tough, roof vents can be used to vent the hottest air while the cooler, ground-level air is brought in from below to provide natural, passive airflow. In the absence of roof vents, a mechanical method must be used. I’m in the process of building a water wall for mine to cool down because I didn’t have the foresight to install roof vents. Put simply, the wall of water is a giant swamp cooler. Water is passed over thick pads made of heavy, coated paper, while exhaust fans draw air through the building. The water cools the air like an air conditioner. This system can be used in any of the structures. There are many ways to heat. Most greenhouses use propane or natural gas heating. I will try a solar oven. The solar oven is a mostly passive solar heater based on the same principle that heats the inside of the structure but brings in the heat from a separate, adjacent structure. A typical solar oven will reach about 200 degrees in winter in Minnesota. This air is pumped into the greenhouse structure.

Rich and I are both trying new things to improve our ability to grow a variety of crops. Sometimes our experiments work and sometimes they don’t. This time, I think we have a good chance of improving our gardening experience. If you have any questions, ask a master gardener. It is what we do.