By ANN HINCH
Assistant Editor

INDIANAPOLIS, Ind. — Want greenhouse benefits without as much expense or property tax adjustments? A high tunnel might be just the thing.

Many organic growers filed in to hear Matt Kleinhunz explain the benefits and drawbacks of high tunnels at the recent Midwest Organic Production & Marketing Conference & Trade Show two weeks ago. The Ohio State University extension horticulture specialist is based in Wooster, Ohio, and has worked extensively in organic and high tunnel production for 10 years.

The high tunnel is similar to the hoop house in structure and size. “It’s the low tunnel concept on steroids,” was how Kleinhunz described it, referring to ground-hugging protective coverings over plants in months of inclement weather.

The organic growers at the conference interested in high tunnels cited a longer growing season – meaning more marketing and income opportunities – weather protection and controlled climate as some of their favorable characteristics.

Kleinhunz defined a high tunnel as one or more layers of durable plastic stretched over a structural frame at least 8 feet tall, made of wood, metal or PVC pipe. The two most common shapes are Quonset (upside-down U) and Gothic, which looks sort of like a house, with an angled roof and defined edges.

Kleinhunz said for his money, the Gothic shape is more desirable, since it sheds heavy loads of snow better than the Quonset, allows one to grow tall produce right against the inner wall (as opposed to having to leave ground space and lose height to the U-curve) and better allows space to mount a vent or heater near the doorway if desired.

A high tunnel can be made for easy transport or affixed to one spot; nevertheless, they are usually counted by tax officials as “temporary” structures and not assessed. The downside is they can’t typically be insured for damage, either.

“In our climate, that kind of matters,” he said, showing a couple of slides of Quonset tunnels caved in by heavy snow and ice. The best shape is a rectangle, Kleinhunz said, with a ratio of at least 2.5-to-1 for the longer sides. The most common type is 96-by-30-feet, and while the figures are slightly out of date, he said construction cost in his region is between $2.38-$7.24 per square foot.

He compared potential cost to the difference between a pickup truck and an SUV: Same basic chassis, but what determines price are the amenities.“It’s the same for a high tunnel,” he said.

These extras vary; some people, he said, go as far as installing temperature sensors that automatically adjust climate control or “call” their phones to alert them to the need to go to the high tunnel and vent the trapped heat. The plastic can be made to roll up, and even the types of plastic vary. For instance, Kleinhunz uses a hard poly on the ends of his high tunnels, but flexible plastic for the long sides.

“I make that investment just because I feel more comfortable with it,” he said.

He said it is generally accepted that plant respiration doubles by raising the temperature just 10 degrees, and even in cold weather, trapped light means heat. High tunnels may offer farmers not just a longer growing season, but more protection for select crops in bad weather – he showed some slides comparing the slower development of outdoor tomato vines after a rainy season, compared to vines in a high tunnel, raised up off the saturated ground.

He agreed with an audience member who pointed out since high tunnels sluice off snow and water, the ground surrounding one will be inundated with more moisture as a result. Kleinhunz cautioned growers to make certain drainage is good in the area around such a structure.

While many high tunnels are put in fields, he pointed out they may work equally well on marginal land or asphalt, since plants may be cultivated in soil in raised beds. Beds can be made of new materials or environmentally friendly, recycling existing materials – Kleinhunz said they’ve been made of everything from old pallets to tires, to corrugated metal.

Finally, he warned not to skimp on the basics, the “nuts and bolts” – literally – of building a high tunnel. He described one he’d seen on which the plastic was attached to every other pole instead of each pole, and a windstorm had lifted the gaps like an umbrella, tearing it apart.

“It looked like Sasquatch stomped on it,” he said.