Building the KSU high tunnel

High tunnels are unheated greenhouses used to extend the growing season. In Kentucky they can allow year-round vegetable production.

In 2005-06 we erected a 30' x 40' high tunnel at the Kentucky State University research farm, using a frame salvaged from a heated greenhouse. The following pictures show the construction process. A table showing the cost of materials is at the bottom of the page. 

Click a picture to see a larger view. Click here for a detailed examination of the effect of this tunnel on microclimate.

September 6, 2005	September 7, 2005
Untreated 2x4s were painted to protect the end wall framing studs. Organic standards do not allow treated wood to come in contact with the soil or crop.	A screen door frame was built to fit inside metal hoops salvaged from a used heated greenhouse.
September 8, 2005	September 13, 2005
End walls included 4' x 4' window frames.	Metal hoops were screwed to each end wall, then aluminum wiggle wire track was attached to the upper edge of each hoop with metal screws.
September 13, 2005	September 13, 2005
The summer cover crop of cow peas was incorporated into the soil at the construction site. Cowpeas were chosen as a heat tolerant cover crop that would add nitrogen and organic matter to the soil.	Anchors of galvanized steel pipe, welded to angle iron, were pounded 2' into the soil to support each end wall.
September 13, 2005	September 15, 2005
End wall frame struts were bolted to the anchor posts.	Workshop participants at the KSU farm field day attached interior hoops to anchor pipes. Anchor pipes had been pounded at an angle, with a wooden block between the pipe and sledge hammmer to prevent the pipe end from splaying.
September 24, 2005	September 24, 2005
Completed tunnel frame.	Frame structural details. Top: End wall struts supported by angle iron and anchor pipe. Bottom: Pipes joined by brackets (left) and sleeves (right).
December 7, 2005	December 7, 2005
Recycled plastic 1x6 toe boards were attached around the house perimeter. A strip of 2x2 ran the length of the house, 2' above the soil surface. Aluminum wiggle wire was screwed to the end wall toe boards and the side wall 2x2. Two layers of 6 mil plastic were draped over the frame, and attached to the end hoops with wiggle wire.	A 60 W blower fan was attached to a hoop, and through the inner plastic layer. Hoses were attached at the corners of the house to allow air to pass between the side walls and end walls.
December 7, 2005	December 7, 2005
Two layers of end wall plastic were attached with wiggle wire (foreground).	Attaching plastic to the frame took about three hours on a calm afternoon.
January 18, 2006	January 25, 2006
An 8' wide paving stone pad was laid atop gravel and sand at one end of the house. An 18" wide path was constructed down the center of the house. Feather meal fertilizer (Nature Safe, 10-2-8) was incorporated into the soil with a roto-tiller at 100 lbs N per acre, and three beds were formed on each side of the center path.	Six-week-old lettuce and kale seedlings were transplanted on one-foot centers.
January 27, 2006	March 2, 2006
Lettuce, beets, radish, and spinach were direct-seeded.	Right bed: Transplanted kale (foreground) and lettuce (background). Left bed: Direct-seeded greens.
March 21, 2006	February 2006 - June 2007
Ready for harvest! Left bed: Transplanted lettuce (foreground) and kale (background). Right bed: Direct-seeded greens.	Temperatures inside and outside the high tunnel.

The plastic accounted for only 20% of the up-front cost, but will account for more than half of the cost amortized over time. The value of crops harvested should exceed the up-front material cost in the first year.