The well thought-out portable greenhouse concept will extend your garden season and boost vegetable production.
Phil Norris’ rolling greenhouse helps extend his growing season without the pest problems of a stationary greenhouse. Norris and Deborah Wiggs operate a 13-acre organic farm on the coast of Maine.
“The first week of March 2014, we were planting inside when the ground outside was still frozen and snow covered,” Norris says. “This year we had a really harsh winter and couldn’t plant until the second week of March.”
Neighbor and experienced rolling tunnel builder Eliot Coleman was a handy resource. He suggested a 48-foot-long-by-22-foot-wide high tunnel that could be easily vented through the end walls.
Norris designed the rolling high tunnel to traverse four 48-foot plots over the course of the year. He bought high tunnel bows and cross members from Rimol Greenhouse Systems. He constructed the framing on top of two 2-inch galvanized pipes laid with a gentle curve to match the site. Rather than lay the pipes on the ground, Norris cut up old pond liner and set the pipes on that. Each bow was pre-tensioned with a come-along and locked at exactly 22 feet wide with a cross member. The bows are mounted on sheaves and roll easily on the rails.
A big challenge was what to do for end walls and an entry door. Norris needed cross framing on the ends for structural integrity when moving the high tunnel. Moving his entry door to the side allowed him to put a steel crossbar at waist height on both end walls with more framing above it.
As winter approached in 2013, Norris covered most of the framework, including the west end wall, with poly. The area above the crossbar on the east end (exposed to battering winds) was covered with rigid polycarbonate.
End walls below the crossbars needed special attention, as the tunnel would need to roll over an existing crop to move into place for planting the next crop during a season. Norris hung poly below the crossbars at both end walls. It was fastened with wiggle wire to a piece of double wire lock positioned 42 inches above the soil.
“When the poly is rolled up, it is well above the lower crossbar, allowing 32 inches of clearance,” Norris says. “Rope loops at the end of the roller secure it (when) rolled up.”
He fashioned a temporary solution for a side door with a flap of poly sealed around the edges with wiggle wire. The next spring, he bent steel tubing to match the shape of the sidewalls, welded up a door frame, and covered it with polycarbonate.
“I hung the 4-foot-wide door with sliding barn door hardware,” Norris says. “The bottom of the door is free and held down by gravity.”
The tunnel is vented with a scissors-type closure at one end. Triangular pieces of polycarbonate with wooden frames are hinged in place in both peaks. Temperature-sensitive hydraulic cylinders start to open the vents at 75 degrees, and at 85 degrees, the vents are fully open.
A wireless sensor in the middle of the high tunnel sends temperature and humidity data to Norris’ office, where it is monitored and graphed.
Thanks to an overhead sprinkler system, the high tunnel also serves as a rolling sprinkler. In a minute he can roll the entire house forward over any of the plots and deliver 1 inch of rain in two hours. Then he can roll it into another position.
Luckily, he notes, it’s easy to move. In fact, he has to tie it down so a breeze doesn’t move it when it is supposed to be stationary. In the winter, he anchors it to six posts on the inside and a post at each corner. In the summer, a post at each corner is sufficient.
For more information, email Phil Norris at email@example.com.
Reprinted with permission from Farm Show Magazine.
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