This year we decided to experiment with building a low tunnel in our community garden plot. The design parameters were 1) something inexpensive and 2) something with components that could be easily stored in our apartment during the off-season. For materials, we went with 3/8 inch diameter wooden dowels, 1/2 inch internal diameter PEX tubing, 4 mil thickness plastic sheeting, large binder clips, paracord, and paint stirrers. After the danger of snow and frost had passed, we later removed the plastic sheeting, washed it, and replaced it with row cover. If this were planned to be a permanent installation we would have done things differently, probably using rebar and PVC pipe for the frame.
Step 1- Ready frame materials: We cut 4 ft. long wooden dowels into 1 foot long sections. The PEX tubing was cut into 70 inch pieces, being careful to reshape the cut ends if they were crimped during cutting.
Step 2- Framing: Hammer a set of dowels halfway into the soil about 2.5-3 feet apart to support the first hoop. Slide the ends of the first piece of PEX into the dowels. Hammer in another set of dowels about 4-5 feet down the row from the first set, and repeat until the tunnel is the size you want it. Ours has 6 loops of PEX, and is around 18-20 ft. long.
Step 3- Measure and cut plastic sheeting: Use at least two large binder clips to attach the end of the plastic sheeting to the first PEX loop. We left the ends open to provide ventilation, but if you are using this for winter gardening you might want to consider closed ends. Unroll the sheeting along the frame, and leave a bit of slack when cutting the sheeting at the end of the tunnel. Hold the plastic sheeting on this end to the PEX frame with binder clips.
Step 4- Secure sheeting with paracord: Tie pieces of paracord to 4-5 paint stirrers using slip knots. The pieces of paracord should be a bit longer the circumference of the PEX frames. Hammer these in on the left hand side of the PEX loops, and throw the paracord over to the other side of the tunnel. Cut 4-5 short pieces of paracord, and tie each to another paint stirrer to form a loop. Hammer these into the ground on the other side of the low tunnel, to the left of the PEX frame. The goal is to have the paracord cross to either side of the PEX frame. Pass long piece of paracord through the paracord loop, tension the paracord, and tie a trucker’s hitch knot. There should be a piece of paracord securing each end PEX loop, but it is ok if not all of the interior PEX loops are secured with paracord.
Step 5- Secure long ends of sheeting: Bury the plastic sheeting along one long end. Put rocks on top to help it stay. Place large rocks on the opposite side to hold the plastic to the ground, which are removed to access the tunnel interior.
Step 6- Add structural support to end PEX loops (optional): We hammered 2 ft. long dowels into the soil at the midpoint of each end loop, and secured them to the PEX. Other options could include using stakes and additional paracord to tension the loops out from the ends of the tunnel.