by Deborah Jeanne Sergeant
High tunnels can provide growers with an economical approach to extending the growing season, starting seedlings and controlling more aspects of growing; however, they can be susceptible to damage if farmers do not take the right precautions. Adam Montri, owner of Ten Hens Farm in Bath, MI, presented “High Tunnel Storm Protection and Routine Maintenance” as a recent webinar hosted by Practical Farmers of Iowa.
Montri maintains six high tunnels on his farm. He said orientation represents the first consideration when building high tunnels.
“A lot of times when we talk about orientation, it’s how to get the best wind flow to vent,” he said. “The other thing to think about, especially if we’re in flat, open areas, is do you have alleys where you get big winds on your farm? Or you’re up on the top of a hill, think about how we can orient these so they don’t get blasted all the time. We’d like them east-west oriented for maximum sun, but if that means they’ll get beaten up over and over, you may want to switch them to go north-south. You’ll have less light, but better longevity.”
Inside a high tunnel, durability relies upon sufficient trusses. Farmers who buy high tunnel kits should make sure their kit comes with enough or they will need to purchase more. “Usually once you get over 22 or 24 feet, you want to make sure you have trusses on those bows,” Montri said.
Like with any farm purchase, comparison shopping before investing in a high tunnel is important. “The one without the trusses will definitely be less expensive so you need to know why,” Montri said. “If you’re in a place that gets any snow load at all, you want to have those trusses. If you’re worried about snow load, have them on every other bow minimum.”
A ridge purlin that runs down the center also strengthens high tunnels. Most kits have five. If you want extra strength, you can add the extra purlin sitting right on the trusses, Montri said.
Wind bracing can also make high tunnels more weather durable. “Adding wind bracing is definitely a good idea,” he said. “If you’re spending even $6,000 to $7,000, adding a few hundred for wind bracing is a good idea.”
Sometimes wind braces will be a long piece that spans over a few bows; other times it will be separate pieces. Montri advised running them diagonally. The fasteners themselves can also make a difference between a short-lived and a long-lived tunnel. He suggested using a band to connect the hip board to the bow or brace bands. Using extra tek screws will prevent the structure’s connections from loosening quickly.
Plastic installation is what makes a high tunnel useful; however, the task is not easy nor a one-person job. You want to make sure it’s tight, but not too snug. Montri said that about 60º is the sweet spot where it will not split or go slack.
“We usually like to attach one end and pull the slack to the other end, do the final end and come back to the first end to make some adjustments,” he said. They’ve also started in the middle, squaring it and pulling it in each direction. By starting in the middle, the team pulls 48 feet of slack instead of 96. He believes that taking one’s time helps get the job done right. “Plastic flapping is not a sound you want to hear,” Montri said.
But splits do happen. “Whenever we buy a new tunnel, we buy a few rolls of greenhouse repair tape. We know we will get holes in it, whether it’s caught on a hip board or screw,” he said. “We need to get them patched as soon as possible. It’s like a little chip in your windshield. It will be small for a while but it will grow.”
He periodically walks his high tunnels to check for tears and holes so they can patch them. Tunnel plastic typically lasts four years, but Montri said in northern climates, farmers can get as many as six out of it.
For those with double-layer greenhouses, Montri advised using inflation fans or blocks of wood or styrofoam to keep the layers apart. Occasionally, the fans will need cleaning and maintenance, but farmers should get them operational again soon. He keeps an extra fan around as an immediate replacement for the next fan that dies.
“As long as we have power, we can have these inflated,” Montri said. “They can take the winds a lot better if inflated than deflated and flapping around, especially if there are two layers.”
Farmers should roll up the sides evenly to prevent damage. That relies upon ensuring the pipes used to roll the sides are in good repair or they will run at varied rates. If they start turning at different times, tearing of the plastic may occur.
To better protect their high tunnels, farmers should use a means of securing the rollups or else a windstorm could tear off the sides. “Instead of $30 in nylon rope and eyebolts, it’s having to replace plastic, hip boards and rollup pipe,” Montri said. “If you don’t get your plastic tight, this can act as another piece of support.” The eyebolts can be drilled through the frame and secured on both sides with a washer and bolt.
Consistency can improve the efficiency of maintenance. “If you’re doing multiple structures, make sure you have all of the same size nuts. It’s not necessary but it makes things a lot easier,” Montri said. He also learned that shorter lengths of rope are better than one long piece. If a section breaks, it’s less rope to replace.
High tunnel doors can open on a hinge or slide in a track. Montri said that the former is easier because there’s no track to clean.
Waterlines and overhead irrigation require maintenance in autumn. “Depending upon where you are, you may have frost-free ones or not,” Montri said. “We have frost-free ones so we don’t have to blow out lines. If they’re not below the frost line you’ll have to blow them out. If they’re frost-free, make sure the drain mechanism is working correctly and that when you turn these off, there’s not any little leaks.”
When the weather is cold, hoses will also need draining or storage in a heated area to avoid bursting them. As another preventive measure, Montri pushes snow away from the sides of his high tunnels and as needed, off its roof with a towel-covered broom.