Tumbledown Farm .9 Acres (give or take an acre or two)

Walk-in Tunnel

WARNING: Hoop House Design Problem, READ THIS PAGE FIRST. I'll post a re-design next year.

After years of frustration over putting the garden to bed in mid-October as the threat of frost went from possibility to probability to killing fact, I decided this year to follow Eliot Coleman's advice and extend the Indiana gardening season by means of a walk-in tunnel or temporary greenhouse.

Amazon's Eliot Coleman Bibliography
With some modifications, I followed the instructions in Coleman's The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener (A gardener's supply book), pp. 210-213 and 217-218.

Materials List for Building a Hoop House or Walk-in Tunnel

Because I am still in the experimental phase, I decided to start small, with parts I could easily bring home in the hatch-back car. The finished dimensions (floor) of the temporary, unheated greenhouse are a mere 8' X 12' (or 8' X 14'). That is wide enough to cover three of my usual garden crop rows with a grass path on either side of the middle row (see the Garden Plan page or the Strawberries page for photos and details).

Parts List (from hardware or home improvement store, 2009 prices in Indianapolis)

• (8) 3/4" X 10' PVC Pressure pipe (Schedule 20), $.99 each (= $7.92 total)
• (10 pack) 3/4" PVC Tee (= $2.24 total)
• (4 oz) Regular Clear PVC cement (=$2.24 total)
• (10 pack) 3/4" Galvanized Pipe Strap (= $1.40 total)
• (4) 3/4" X 18" Nail Stakes with pre-drilled holes, $2.53 each (= $10.12 total)
• (2) 2" X 6" X 8' Studs, $2.39 each (=$4.78 total)

Subtotal Hardware Store (with tax = $31.33)

Specialty Mail-Order Parts from Garden Supply (FarmTek, 2009 prices)

• (2) 1.25" X 8' Aluminum U-Channel (= $15.68 total)
• (2) Spring Fastener for Aluminum U-Channel (= $3.70 total)
• 30' L X 20' W (6 MIL) Clear Greenhouse Film (poly) (= $68.70 total)
• (2) Hi-Low Memory Thermometer, $10.949 each (= $21.90 total)
• Shipping (= $28.65 total)

Subtotal Mail-Order (= $138.63)

Total cost of materials was $169.96 (which, divided over the expected 3-year life of the tunnel, would be an investment of $56.65 per year in fresh winter salads and vegetables). Since the poly is the biggest expense (and I bought enough for a tunnel twice as long as the one I have), I could easily double the size of the experiment next year at very little additional cost. Whether it is worth the effort and expense depends on one's hankering to be out in the garden during the winter and to eat fresh greens year round! The thermometer isn't, strictly speaking, necessary--but it will be useful to report on this page the temperature differential between the high and low temperatures outside and inside the tunnel.

Assembling the Frame for a Hoop House or Walk-in Tunnel

Assembly of the frame was relatively easy and accomplished in a matter of hours. The most significant time factor was waiting for the glue to dry on the two sets of PVC joints.

Notice the difference in orientation between the second PVC Tee as it is attached to the center section of pipe (#2 in the photo) and the orientation of the PVC Tee attached to the pipes on either end of the tunnel (#1 and #3 in the photo).

The final step in pre-assembly is to cut the remaining two sections of PVC pipe to an appropriate length and attach them to PVC Tees #1 and #3 as hoop spacers (see the two photos above). The hoops will be connected to one another at the apex of the tunnel (held together by bungee cords connected to the necks formed by the two PVC Tees between the hoops and the spacers; see the photo below). These spacers keep the hoops from collapsing in either direction, either outward or in upon one another. They also provide another means of keeping the poly from sagging between the hoops and help support the weight of the poly more evenly.

The galvanized pipe straps should be attached to the 2" X 6" X 8' stud using the same measurement as for the spacers (see paragraph above). In other words the bottom ends of the hoop pipes should be spaced the same as the pipes are at the apex of the hoop. See the two photos below for an example.

After the 8' aluminum U-channels have been attached to the top of each 2" X 6" X 8' stud, and holes have been drilled in the stud at appropriate intervals to allow the attachment of the stud to the nail stakes by means of a heavy gauge wire, the boards may be placed parallel to one another at a distance of 12' to 14'. The nail stakes are driven into the ground until the top of the stake is roughly the same distance from the ground as the top of the stud. Wires are then used to attach the boards to the stakes, so that they will not move in a heavy wind. Holes are drilled in each of the ends of the PVC pipes and they too are wired to the boards, running the wire through the end of the pipe at a point below the pipe straps through which they have been inserted.

Finally, the poly is unrolled and attached to the U-channels by means of the springs. This completes the assembly. The ends of the poly may be kept in place using bales of straw or stones (or both), or by tying the poly together and attaching each end to a stake.

Now all there is to do is tend the young plants as they develop this fall and see whether we can be harvesting greens and beets, and carrots for Thanksgiving and Christmas dinner!