5 Simple Steps to Build Low Tunnels

Grow greens and root vegetables all winter long by extending the season with low tunnels over your raised garden beds.

by Jessica Walliser
PHOTO: Jessica Walliser

I’m always looking for ways to extend my harvest into late fall and even through winter. Covering cold-tolerant crops like lettuce, kale and other greens, as well as root crops like carrots, turnips and parsnips, with a fabric row cover or plastic sheeting can provide frost protection down to 20 below zero. With protection like this in place and a layer of straw mulch nestled around the plants, year-round harvests are practically guaranteed for many parts of the country.

In in order to properly protect crops from frost, the covering must remain above the plant tops with a layer of insulating air sandwiched in between. If the icy-cold plastic or fabric comes in contact with plant leaves, foliage burn could result. To remedy this problem, it’s a good idea to build a small hoop tunnel over the beds to hold the fabric above the plants. Here is one easy way to build this kind of hoop tunnel over a wood-framed raised bed.

Step 1

Purchase enough rust-resistant, deck-mounted flagpole holders to position opposing pairs every 3 to 4 feet down the sides of the bed. Both end pairs should sit flush with the ends of the bed. I prefer metal flagpole holders to plastic, as they last longer. Be sure to place the pairs so they’re exactly opposite each other. Pre-drill holes into the wood in the appropriate positions, and then screw the flagpole holders into place.

Step 2

Purchase enough flexible PVC pipe to form half-hoops over the bed: one half-hoop for each set of opposing flagpole holders. The top of the hoop should be a minimum of 18 inches above the soil surface; higher hoops will provide for taller plants.

Before you purchase the pipe, be sure it fits into the opening of the flagpole holders. It should be snug but also lift out and insert fairly easily. Cut the pipe to the proper lengths.

Step 3

Purchase one long piece of 1-inch-diameter PVC pipe. This piece should be long enough to extend down the full length of the bed from the half-hoop at one end down to the half-hoop at the other.

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Step 4

Place a half-hoop in each opposing pair of flagpole holders. Position the long, straight piece of 1-inch PVC pipe just beneath the hoops. It will serve as your top, central support. Attach the peak of each hoop to this long PVC piece with plastic zip ties (as shown in the photograph).

Step 5

Cover the hoop frame with heavy-weight floating row cover or plastic. Weigh down the edges and ends with rocks or bricks to form a secure, closed tunnel. On warm days, the plastic or fabric can be opened on the ends to allow for air circulation. Harvests occur by simply removing a few of the bricks and lifting up the cover.

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