To make the low tunnels, we started with half-inch metal electrical conduit and made
three 60-degree bends with a conduit bender to create a house shape — straight side
walls (6 feet apart) and “roof” sections slanting equally to both sides. We assumed
we would have enough support if we used one hoop every 5 feet. We then covered this
prototype with a 10-foot-wide floating row cover held down along the edges with sandbags.
We found that holding the edges of the fabric with sandbags is much less work, much
faster and almost as secure as burying the edges. We fill each bag with 12 to 15
pounds of soil, sand or gravel.
A few windy days showed us a weakness in this design. The row cover fabric was stressed
where it was pulled tightly against the three bends of the house-shaped hoops and
was torn in a few places. We realized that a smooth, round shape for the hoops would
Our next step was to make the hoops out of half-inch hard-plastic conduit. By making
10-inch-deep holes with an iron bar every 5 feet along the outside edges of the two
beds, we could insert an end of the plastic conduit into one hole and carefully bend
the conduit into a half circle, inserting the other end into the corresponding hole.
The first time we put up the plastic hoops, two people working together made the
process easier: one holding the first end vertical while the other bent the conduit
and inserted the second end as vertically as possible. After being used for a while,
the conduit acquired a reasonably curved shape that made erecting the hoops an easier
job for one person.
We put hoops over the onion beds in mid-October. Realizing the tunnels would have
to survive the weight of winter snow and that we were now using plastic instead of
metal conduit, we doubled the number of hoops by placing one every 2 1/2 feet along
the row. We covered the hoops with row covers after we put them up, and the onions
continued growing. But for the serious winter weather that would be starting by late
November, we knew we needed a stronger material than the floating row cover fabric.
We had just re-covered a greenhouse, and the old plastic still had a little life
in it, so we cut it into 10-foot wide strips and set them aside to use when the weather
got colder. We planned to place the plastic over the fabric in order to give the
low tunnels a smooth, strong surface for the snow to slide off.
The final step, completed around Thanksgiving, was to add the plastic and stiffen
the structures against the weight of winter snow to come. We drove a 2-by-4 stake
into the ground 3 feet from the end of each row and tied a rope tightly around the
bunched end of the plastic covers (see illustration in the Image Gallery). We then
pulled the ropes as tightly as we could from both ends to make the cover taut and
tied the ropes to the stakes. We replaced the sandbags to hold down both the plastic
and the fabric.
Both that first winter and again this past winter, the snow here on the Maine coast
did not disappoint us, and the quick hoops got a real test. With the exception of
one end of a row where the snow drifted excessively and pressed a few of the plastic
hoops down to the ground, the 30-inch high tunnels survived a number of 18-inch snowfalls
Even Better Designs
Are we satisfied? Of course not. We recently perfected a tubing bender to create
the ideal curved shape from half-inch metal conduit. With the proper curve, metal
conduit hoops with almost straight sides extending 6 inches or so above the soil
come closer to the ideal shape. We need only half as many hoops (back to the 5-foot
spacing) to hold up under the snow.
Pre-bent metal hoops help in another way. The plastic conduit tends to lean in toward
the beds where it’s inserted into the soil, because of the forces against it. The
leaning reduces space along the edges of the beds when we use the hoops for protecting
other crops that need more headroom, such as early brassicas, beets, carrots, lettuce,
melons and zucchini — in both spring and fall.
We always strive to achieve our goals in the least expensive way. Quick hoops do
well in that respect. Using the quick hoop system, we can give winter protection
to 1,000 square feet (the size of a 20-by-50-foot greenhouse) of overwintered crops
for about $100 — only 5 percent of the cost of protecting that area with a greenhouse.
(The cost for our low tunnels is about 10 cents per square foot.)
Which crops work well under quick hoops? Spinach would be an obvious candidate. New
England growers have traditionally sown outdoor spinach in the fall, giving it a
little protection with evergreen boughs, in order to get an extra-early harvest in
spring. Many other hardy greens, such as lettuce, could also be planted in the fall
for early spring harvest. We have often seen our latest-planted baby leaf salads
for fall harvest successfully winter under a layer of snow and come up again in the
spring much sooner and more vigorously than a spring-planted crop could ever do.
Because one can’t count on snow cover, quick hoops are an excellent substitute. And
what about a late-fall sowing of early-spring crops such as peas, carrots or beets?
Hopefully, they would survive to germinate and start growing a month or two ahead
of schedule — in the protected shelter of the low tunnel. A new idea always leads
us to more new ideas.
One more important thing: Think about venting the hoop tunnels so they don’t overheat
when the sun returns in late winter. We simply remove some sandbags in a couple of
places and use stakes with a V-notch in the top to hold the plastic and fabric a
foot above the ground. By the end of March, we remove the plastic layer on each hoop
tunnel and store it for future use. At that point, we have a fabric-covered low tunnel
that we leave in place until it is no longer necessary or we need to move the hoops
to another crop. It couldn’t be easier.