Building low tunnels over existing garden beds can extend the growing season and protect crops from insect damage.
Step 1: Prepare and plant garden beds that are between 30–36 inches wide and spaced at least 3 feet apart. Extra spacing between beds increases accessibility.
Step 2: Use 10-foot lengths of half-inch metal conduit or half-inch PVC pipe to create hoops along each garden bed. Longer lengths of pipe can span multiple rows or make taller tunnels, but they are not as easy to work with and are often cost-prohibitive.
Step 3: Use a digging bar to poke 12-inch-deep holes at 5-foot intervals along both sides of the garden bed or drive 24-inch pieces of rebar 12 inches into the ground at similar intervals.
Step 4: Use a pipe bender to shape the metal conduit into arches and insert one leg of the conduit into each hole or over the rebar stakes on either side of the bed. For PVC pipe applications, station one person on either side of the garden bed and gently bend the pipe into shape, placing one end into each hole or over the rebar stake on either side.
Step 5: Drive a stake into the ground 5 feet in front of and another 5 feet in back of the garden bed.
Step 6: Create a “backbone” for the structure by looping a section of clothesline rope around the top point of each arch, pulling it tight between arches and leaving a fair amount of rope on either end.
Step 7: Pull the rope taut and tie it securely to the stakes both in front of and in back of the tunnel.
Step 8: Cover the tunnel with a length of floating row cover. Weight the row cover down along the sides of the tunnel with sand tubes, rocks or lumber.
Step 9: Add extra support to the structure by pulling the row cover taut on either end, bunching it together and tying it off on the stakes at the front and back of the tunnel.
Step 10: To extend the growing season in colder climates, add a layer of clear plastic over the top of the floating row cover and weight it down on the sides with the same sand tubes, rocks or lumber. Roll the plastic back on sunny days to prevent the tunnel from overheating.