*These guidelines will allow you to construct a simple backyard "tunnel" style greenhouse that can expand your gardening possibilities. A backyard greenhouse can extend the growing season and, in cooler climates, allow you to grow plants that would not normally survive. In warmer climates, year round gardening may now become a reality. In addition to altering growing conditions, a backyard greenhouse provides protection for delicate plants by blocking wind and rain as well as preventing frost from forming.
• Plastic Poly Sheeting roll of desired size and thickness
• 3/4" PVC (or metal tubing)
• PVC primer and glue (if using fittings)
• Fasteners (clamps/wire ties)
• At least one assistant
1. Find the ideal spot. Choose flat, level area that gets plenty of sunlight, but is protected from strong winds.
2. Decide on a size. Once you have determined the footprint of your greenhouse drive rebar stakes into the ground at all four corners. The stakes should go 1 to 2 feet into the ground with anywhere from 2 to 4 feet protruding above ground depending on the overall size of the greenhouse (taller/wider structures will need more support.) From here you will need to decide how far apart the support "ribs" will be. This can range anywhere from 2 to 4 feet depending on the strength of the wind and the amount of snow/rainfall in your area. If your region experiences more than 4 inches of snow on the ground at a time it is recommended to place the stakes closer together to avoid having the greenhouse potentially collapse. Once you have determined the distance you will have between the supports, drive additional stakes down the length of the footprint of the greenhouse, one on each side for each support rib.
3. Building the frame. For this tunnel style greenhouse, the ribs are constructed using either PVC or metal pipe. The width, length and height of the greenhouse will dictate what materials you will need. PVC will be the easiest to work with as it will easily flex to the shape you are trying to achieve. 20' lengths of 3/4" PVC can be bent into one large arch, or 2 shorter pieces can be joined at the top using a coupler. Once the ribs have been constructed, slide them over each stake. At this point, a center support brace along the top can be added to provide additional stability. If using smaller pieces of pipe and fittings, you can add several shorter pieces of pipe to connect all the ribs along the top. If using whole lengths of bent PVC pipe, one single length of pipe across the top secured with clamps or heavy duty UV resistant wire ties will do.
4. Putting on the plastic. Using either 4mil or 6mil clear poly sheeting (6mil is recommended for durability), drape the plastic sheeting over the frame. Leave an extra foot or two on the sides to help secure the plastic and trim any excess. There are several ways the plastic can be secured. An easy way to secure the sides is to screw 2x4s (any similar size scrap lumber will do) to the bottom and roll any excess up with the wood until the plastic becomes tight along the frame of the structure. The plastic wrapped wood pieces can then be buried to help anchor the greenhouse. The plastic can be secured to the front and back ribs with clips or wire ties. If you care to add simple doors to the ends, hang strips of plastic cut to the width of the frame from the front and back ribs prior to draping plastic over the entire greenhouse. Leave an extra foot or two at the bottom to anchor the flaps in place. Cut a slit down the center to create a simple opening. On hot days the flaps can be clipped open to help cool the greenhouse. Larger greenhouses can have more elaborate doors and windows put in with a little extra work.