Row Cover Hoops: PVC tunnels frost protect

Creating a low tunnel with PVC hoops is an effective way to shield plants from frost. The structure traps daytime heat radiating from the soil, keeping the air around your plants several degrees warmer than the ambient temperature overnight.

To construct the tunnel, you will need 1/2-inch or 3/4-inch Schedule 40 PVC pipe, 3/8-inch or 1/2-inch rebar cut into 24-inch lengths, and a floating row cover or frost blanket of appropriate weight for your climate. For a standard 3-foot wide garden bed, a 10-foot length of PVC pipe cut in half creates two 5-foot hoops, which will form a tunnel with adequate height.

Begin by driving the rebar stakes into the ground on both sides of the row you intend to protect. Pound them about 12 inches deep, leaving 12 inches exposed. Space the stakes every 4 to 5 feet down the length of the bed, ensuring that each stake has a corresponding partner directly across from it.

Next, take a pre-cut section of PVC pipe and bend it into an arch, slipping each end over a rebar stake. The rebar acts as an anchor, holding the base of the hoop securely in place. Repeat this process for all pairs of rebar stakes to form the tunnel's framework.

Once the PVC frame is assembled, drape the row cover fabric over it. Ensure you have at least 12 inches of excess fabric on all sides. Pull the fabric taut over the hoops and secure it. The most crucial step for frost protection is to completely seal the tunnel to trap warm air. Bury the long edges of the fabric with a continuous line of soil, or use rocks, bricks, or sandbags placed end-to-end to weigh it down. Any gaps will allow cold air to enter and defeat the purpose of the cover.

Secure the fabric to the end hoops using snap clamps or large binder clips. Gather the excess fabric at the two ends of the tunnel, twist it closed like a bread bag, and weigh it down or tie it to a stake.

During the day, especially on sunny ones, temperatures inside the tunnel can soar. It is essential to vent the tunnel by lifting one of the long sides to prevent overheating your plants. Be sure to close and seal it again in the mid-afternoon to trap heat for the coming night. The weight of the frost blanket matters; a heavier fabric offers more degrees of protection but allows less light transmission, so choose based on your specific frost intensity and crop needs.