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. |
Cost of high
tunnel materials
|
| Material |
Cost |
Expected
life
(years) |
$
per year |
¢ per
square
foot per year |
Salvaged hoops
(estimated value)
Wiggle wire & track
Paving stones
Plastic boards
Screen doors
Lumber
Fasteners
Paint
Fan
Plastic |
$1,020
$250
$380
$300
$250
$160
$60
$30
$100
$660
|
20
20
20
10
10
10
10
10
10
4 |
$51.00
$12.50
$19.00
$30.00
$12.50
$16.00
$6.00
$3.00
$10.00
$165.00 |
4.3¢
1.0¢
1.6¢
2.5¢
1.0¢
1.3¢
0.5¢
0.3¢
0.8¢
13.8¢ |
| Total |
$3,210 |
|
$325.00 |
27.1¢ |
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.
