Low tunnels with floating row cover provide all kinds of benefits to young plants in the garden. The list of attributes is indeed long: shelter from drying winds, winter cold protection, hiding plants from hungry deer, softening intense sunshine. The challenge can be to keep all these wonderful benefits and keep the fabric in place despite gusting March winds that would send your fabric flying, and winter snows that could quickly collapse your tunnel.
We would like to share a design for a cost-effective low tunnel that we have been improving and found very effective over the past few winters, with the added benefits of: not using any kind of weight to hold down the fabric, allowing the sides to be pulled up and held in place for easy weeding or harvesting, and being feasible in challenging spaces (in our case, curved rows necessitated by farming on contour lines).
We have built these from the full 10’ length of the conduit (for wide or double rows), and, when we need a twofer, we have shortened the length of the conduit to 6.5 feet (for a single row) and used the remainder of the conduit as trellising support.
Materials and Cost for a 100’ low tunnel
• 1/2” conduit bent into hoops (18 at $3.20 each, $57)
• 100’ row cover (we use Typar T-518, 15’ wide, $83)
• Self-tapping metal screws (Teks #8×3/4”, 150 count, $7)
• Baling wire (or electric fence wire, scraps)
• Braided nylon rope for purline (Blue Hawk 110ft, $8)
• Twine (plastic or some material that doesn’t stretch much)
Total Cost ~$150
1. Bend the conduit into hoops using a Johnny’s Low Tunnel Bender or similar tool. Even a conduit bender available at your local hardware store will work.
2. Using wire, make a set of wire loops about the size of your wrist, two for each hoop.
3. On each hoop, about six inches from the bottom, drill a self-tapping metal screw into the conduit, leave a gap between the screw and conduit.
4. Wrap a wire loop around the conduit at the base of the screw; be sure that the twisted wire ends face in (these could rip your fabric).
5. Push conduit hoops into the soil over the row you want to cover. Use one hoop approximately every six feet.
6. Pound in a t-post or row anchor on each end of the row.
7. Install a purline by tying a good piece of rope to one anchor post then looping around the high point in the middle of each hoop, pulling tight as you go, and finally tying the rope to the anchor at the other end of the row.
8. Pull row cover over the hoops and tie down the fabric onto the anchor post on each end of the row, pulling tight. You can use the tail of the purlin rope to help tie up the fabric.
9. Thread the twine through each loop, passing the twine over the top of the row cover, keep the twine tight as you go. It helps to have two people, one on each side of the row. Adding carabiners to the hoops could make this step faster, but more expensive (then you could clip in the twine instead of threading it through the loop).
We cut the twine into somewhat manageable pieces, then use a fisherman’s knot to tie the two ends together. Small aside on the fisherman’s knot: this knot is used to quickly tie two ropes of equal diameter together, and is incredibly useful. Wonderful illustrations can be found at www.netknots.com/rope_knots/fishermans-knot
Kits for somewhat comparable tunnels are on the market, generally for about twice the cost. (100’ Low Tunnel Kit (#TFLEX 100) from Berry Hill Irrigation for $375.00).
The finished tunnel creates a lovely microclimate for overwintered annuals to flourish. Tunnels are very strong; I have seen one withstand ten inches of snow (that’s a lot for us and about as much as we ever get here in the South) and we were just whipped by a storm with 35mph winds with no trouble on the tunnels. I have even seen a baby goat jump on top of one of these tunnels (more than one species of “kid” was involved with that particular adventure!).
As our winters have become progressively wetter and grayer, I also find it particularly useful to be able to open the tunnels a few inches for better airflow to reduce the horror of fungal diseases getting established. Another potential use for this low tunnel design would be to replace the row cover with insect netting or shade cloth to provide alternate beneficial microclimates in the summer.
While we have (and love) high tunnels and larger caterpillar tunnels, we still find a need for low tunnels for several niche uses on our farm. For example, it is ever my dearest ambition to have as long a ranunculus season as possible in the spring. Ranunculus (and many other hardy annual flowers) do best with a long, cool season to get established, but then, the blooms can come and go in a much too brief burst of color in the spring (especially if the spring is a hot one, not unusual here). To prolong the bloom season, I like to plant ranunculus in multiple microclimates in the fall, with a mid-October planting of sprouted corms in a hoophouse and in a low tunnel. Though they are planted at the same time, the corms planted in the low tunnel generally bloom a month after the corms planted in the hoophouse and still have the benefit of a long period to establish.
We have found this tunnel design a reliable and useful tool for growing quality cut flowers, and hope others might also benefit and have a little less anxiety when those winds come through!
Renee and Matt Clayton
own Wild Scallions Farm
Renee and Matt Clayton own Wild Scallions Farm in Timberlake, North Carolina. Contact them at [email protected]