   Building a Hoophouse - October 21, 2009 Jeff Schalau, Associate Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County Hoophouses are small, semi-portable, greenhouse-like structures that can be used for starting seedlings and for growing vegetables. A hoophouse provides frost protection, limited insect protection, and season extension. They are easily constructed and can last many years. Hoophouse dimensions can be adjusted to fit personal needs and available space. A small hoophouse may be 4 ft x 10 ft and a larger design could be 10 ft x 42 ft. Small hoophouses are ideal for small raised beds while larger designs can be built over existing garden beds. Either way, you can extend your growing season and have fresh vegetables most of the year. The most common, inexpensive designs use hoops of PVC pipe to support the plastic cover and two end walls that provide access and stability. In Arizona, it is also important to design it so that the sides can be rolled up to provide ventilation during warmer weather. The design I will focus on in this column is 10 ft x 42 ft and moveable to facilitate crop rotation. It has clear plastic doors that can be rolled up for additional ventilation and the estimated cost for materials is about $350. This column will reference a web-based publication from Washington State University that contains a materials list and greater detail needed to actually build the hoophouse. It is best to begin by building the two ends which should be identical. Treated lumber can be used where the wood will be in contact with the soil. Corrugated plastic (greenhouse grade) is attached lining up the ridges horizontally, to fit the ends of the hoophouse. Fitting the corrugated plastic horizontally provides added strength to the ends. Overlap the top piece of corrugated plastic a few inches over the bottom piece to keep the ends weatherproof. Brace each side of the doorway with a two-by-four cut 60” long with the ends cut at a 45° angle. The braces are attached to wooden stakes driven into the ground inside the hoophouse. The placement of the door and several helpful hints are detailed in the WSU Publication. On larger hoophouses, all the hoop pieces should be 3/4 inch Schedule 40 PVC pipe. Gases that escape from the PVC pipe contribute to the deterioration of the polyethylene plastic. To prevent “offgasing,” paint the PVC pipes with white latex paint. For a 10 ft x 42 ft hoophouse, you will need 17 lengths of PVC cut down to 18 ft in length. Using a 10 ft spacing with 18 ft lengths of PVC pipe will create a 6 ½ ft height in the center of the hoophouse making it easy for most people to walk inside. Once the ends are built, a 10 ft x 42 ft area can be staked off and the ends placed and secured to the ground. It is fairly important that the corners be square – this can be checked by measuring from corner to opposite corner crosswise. The PVC hoops are secured to the ground by pounding 18 inch lengths of ½ inch rebar 12 inches into the ground. These will be to place each end as well as every 3 ft along the 42 ft sides. Gently slide the 18 ft lengths of PVC over the 6 inches of rebar that remain above ground to place each hoop. Strong nylon twine is used to tie the ends and each hoop from end to end of the house. The twine provides stability and will prevent the plastic from sagging. The plastic sheeting should be at least 6 mil thick and UV resistant. Attach the plastic sheeting to one end and pull it tight to the other end and attach it (again, pointers are included in the WSU publication). Nylon twine is tied to the rebar stakes and run on the outside of the hoophouse for added stability and to keep the plastic taut. The twine should be just loose enough to allow slipping the polyethylene plastic up when raising the sides of the hoophouse for ventilation. This design is for a large hoophouse, but can be scaled down in length to fit smaller areas while using the same ideas. There are many photos and plans available on-line. Washington State University has an excellent, free publication at: cru.cahe.wsu.edu/CEPublications/em015/em015.pdf. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at cottonwoodmg@yahoo.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |