High tunnels help extend growing season

Lacey Jarrell/Capital Press Oregon Valley Greenhouses owner Ivan Schuening explains how maintaining a 4-foot sidewall in polyfilm high tunnel construction ensures even heat distribution throughout the grow area.

First-time produce growers should start out with a basic structure and worry about adding stuff later, according to Ivan Schuening, owner of Oregon Valley Greenhouses in Aurora, Ore.

According to Schuening, high tunnels made out of a steel frame, high-strength polyfilm and wirelock to secure the film to the frame, are the most efficient outdoor grow structures. He said builders on a budget can even build their own frame ends out of wood.

“I’d say 99 percent of the farms and people put their own up,” he said, adding that most growers have their tunnels up early enough to get a fall crop in.

According to Schuening, high tunnels are in high demand because they increase the growing season by about a month and a half, and according to Oregon law, any winter protection or high tunnel with just a polyfilm cover is exempt from building codes if a property is zoned as a farm.

Schuening pointed out that some counties overrule state law, however, and he emphasized the importance of calling the county to find out what a property is zoned and what the required setbacks from roads and property lines are.

Canan Garner, a sales associate at Samurai Greenhouse in Albany, Ore., said if regulations restrict the size of what can be built, growers may be able to scale down or break their concept into smaller greenhouses that add up to the same square footage. He said there isn’t necessarily one type of house that works better than others, but it’s important ensure there is enough air space for temperature control.

“If you end up with not enough height in your (grow) house, your plants might overgrow the space and it gets really, really hot in the summer,” Garner said.

High tunnels are primarily used for lengthening growing seasons, keeping the rain off and warming the soil earlier in the spring, Schuening said. High tunnels are usually not heated or cooled, and converting one into a 12-month growing house with heaters and circulation fans makes it a permanent structure subject to code regulations.

Garner said many tunnels are temperature regulated with roll-up sides and shade cloths will cut down on light transmission and help reduce heat inside a tunnel, as well.

“Doors and roll-up sides are pretty much the standard way to go if you want to stay away from using any sort of electricity,” Garner said.

Schuening said he recommends at least 4-foot sidewalls on high tunnels to maximize grow space and to ensure even heating throughout.

“If you do a hoophouse and no sidewall, you’re wasting 8 feet. So on a 30-foot wide, you’re losing 2 to 4 feet on each side that you can’t grow in, so you’re really down to about 22 feet of growing,” Schuening said.

Schuening said main factor in determining what kind steel frame a tunnel should have is the climate it’s being built in, such as a heavy snow or wind area. He suggested finding out the record snow level to determine what diameter of tubing and wall thickness a high tunnel needs.

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