Low tunnels are important in the late fall, winter, and early spring to protect plants from the harsh winter elements.  According to UMass Amherst, low tunnels can be used to overwinter some of the hardier late fall crops, such as “those crops of the Brassica [e.g. broccoli, cabbage, etc], allium [e.g. onions, garlic], Chenopodia [e.g. spinach], and umbel [e.g. carrots, dill, fennel, etc] families.”  In our climate here in North Carolina, USDA plant hardiness zone 7b, root crop vegetables, such as garlic and onions tend to survive well without the need for low tunnels.  A heavy mulch on onions and garlic help them survive throughout the winter.  Low tunnels in North Carolina, however, are especially important for some other root crops and leafy greens.  Low tunnels are a particularly useful tool for farmers, because they help the farmer grow throughout the year.  Hoop houses, which are larger in scale, serve this same purpose.  (For more details on hoop houses check out this earlier post by Lee Miller on how to build a hoop house at a low cost).  By extending the season with low tunnels or hoop houses, a farmer can generate more profit and have a steady supply of produce throughout the year.  For us here at Duke Campus Farm, low tunnels and hoop houses are especially important, because we want to provide the dining halls on campus with produce throughout the school year while students are on campus.

The great news… low tunnels are very easy to make AND cheap!  At the Duke Campus Farm we recently constructed low tunnels for our asian greens and our parsnips.  The winter is coming soon, so we have to be prepared.  Check out these easy steps on how to make a low tunnel, and – if you haven’t already- put up your low tunnels soon!

Materials

1/2” PVC cut into 5 feet pieces.  We bought “Charlotte Pipe 1/2-in x 10ft 600PSI Schedule 40 PVC Pressure Pipe” from Lowes.  You want to space each “hoop” of the low tunnel about 6 feet apart.  Therefore, for our 100ft rows we needed about 17 pieces.  Because we bought 10ft pipe, we only needed 9 pipes for a 100ft row.  At Lowes this cost us a total of $16.11.

1/2-in x 2ft steel rebar pins.  You will need 2 rebar pieces per “hoop.”  For example, for our 17 “hoops” for our 100ft row, we needed 34 pieces.  At Lowes each pin is $2.04.  Therefore, for a 100 ft row and 17 pins it costs us a total of  $69.36.

Spunbonded row cover.  This is the material you will lay over the hoops to protect the plants from the winter elements.  For our rows we needed 100 feet of row cover.  You generally want the row cover to be a little longer and a little wider than the row is long and wide. This will allow you to drape the row cover over the hoops.  Our row covers were about 105ft long and about 7.5ft wide.  This may be a special order you have to make online, unless you have a specialty sustainable farm supply store in your area.  At our local specialty sustainable farm supply store it cost us $65 for a 250ft roll.  The row cover we ordered was called AgroFabric 34 (90″ width).

TOTAL COST FOR A 100ft LOW TUNNEL = $150.47

Directions

Place each rebar piece in the ground at about a 35-45 degree angle inward.  For each hoop there are 2 rebar pieces that will face each other.

Space the rebar pieces 6 feet apart along the row.

                                                         Bend pvc pipe over slanted rebar pieces.

Cover with row cover and weigh down the row cover with weights on either side of low tunnel.  Rocks work very well.

Now your plants are protected from the cold winter elements, and you can keep growing into the the winter months!

What This Is

I wrote this post with the hope of helping small-scale farmers build a large, sturdy and economical high tunnel. This design is perfect for winter growing, and can also be used (with a shade cloth replacing the poly skin) for season extension in the summer.

Our high tunnels are 100’ long and 12’ wide, to suit our 100-foot bed length and 3’ bed width with 1.5’ aisles (3 beds per tunnel). The total cost is about $1500, which is a steal for a high tunnel this size (even if it is a few bucks more than the designs it’s based on, for reasons we’ll discuss down the page). Better yet, this is a project that three people could easily manage in a day, even on the first try.

With a little practice you and your two friends could pop up three of these in a good day.

This post relies on two links, in particular: first, Johnny’s excellent 27-page guide to building a high tunnel; and second, Mother Earth News’ diagram of a high tunnel end wall frame.

What To Do

If you want to build our high tunnel, here’s what you do. First, check out the materials list and order what you need (but don’t actually do this first–go ahead and read through everything). Second, proceed as if you were going to build Johnny’s high tunnel, until you get to page 17, where they tie off the plastic in an unsightly and ungainly ponytail and wedge it between two T-posts. Don’t do that.

Instead, follow Johnny’s high tunnel construction plans about 80%. Basically, we build the tunnel according to Johnny’s excellent plans until the very end, when it comes time to tie off the plastic on the end walls. For this step, we use a simple framing approach recommended by Mother Earth News (MEN) and many others.

The advantage of Johnny’s plans is that they are geared toward a simple, strong and highly economical structure. For example, where MEN uses PVC pipe to construct the bows, Johnny’s uses steel fence rail. And instead of requiring hundreds of feet of wiggle wire/track, Johnny’s uses a nifty lacing of parachute cord (total cost: $50) to hold the plastic in place while allowing for easy adjustment up and down.

The disadvantage of Johnny’s plans, as far as we’re concerned, is the absence of a door (or doors). Instead, the ends of the poly skin are simply tied off and staked down. Users crawl in and out under the liftable poly cover on the sides. There’s nothing wrong with this approach. However, there are two disadvantages that led us to build proper end walls with working doors.

First, Johnny’s design assumes two extra aisles inside the high tunnel, one on each side. We prefer to maximize the growing space and run our beds to within inches of the side. In so doing, we actually get a lower cost/square-foot of growing space as compared to Johnny’s design, despite the extra $150 or so it costs to build the end walls. Second, it seems truly inconvenient to slide under the poly skin every time you want to get in or out, especially if you are toting tools/harvest bins/wheel barrows with you. It just seems like a really easy way to put a hole in the (expensive) poly siding.

Enter the MEN’s plans. Many people have built a simple frame for their end walls, but we chose to highlight the MEN diagram for its simplicity. The end wall frame is constructed of treated 2×4’s, with a bottom end board of treated 2×6. You can easily adjust the dimensions to suit the particular widths of your high tunnel and, especially, your door.

Now for our own design touch. We then run dual-track wiggle-wire channel along the top arc of 2×4 frame, and a single-track channel along the doorframe and the 2×6 on the ground. This allows us to attach the large poly skin to the top of the double-track, and then cut pieces of poly to fit on either side of the door.

Materials

This greenhouse materials spreadsheet (including links to all the materials) should get you started. (If you decide to lengthen/shorten your high tunnel, check out Johnny’s helpful worksheet, which customizes most of the material list depending on the length you’re trying to build).

Note that some of the materials for this project are from Johnny’s. Their pole-bender is a good investment at $60 even if you’re only planning to build one high tunnel, because it allows you to make near-perfect bends in any standard 1-3/8” top rail fencing. The first time we built a high tunnel, we bent all of the bows by hand using a jig we rigged up from two T-posts and a telephone pole (the result was impressive considering, but the time and stress were nothing near worth it). Johnny’s also sells a nice piece of poly cover (24’ x 125’) that will work very nicely for this 100’x12’ design, including enough extra material on the ends to cover the end walls. If you’re looking to save a little money, these plans replace Johnny’s film with good stuff from littlegreenhouse.com, which shaves about $50 off the total cost. Finally, Johnny’s sells the appropriate cross-connectors that will attach the bows to the ridgeline. These can be hard to find elsewhere in the proper dimensions, and again, they are reasonably priced at $5 for two.

We’ve listed Farm Tec as a good supplier for wiggle wire and the wiggle wire track. This stuff is not cheap at over $1/ft, but good luck finding it cheaper anywhere else. If you do, get in touch!

Just for kicks, I’ve linked to Bolt Depot for all of the (literal) nuts and bolts required for the project. They are a great resource for any kind of fastener, and they have excellent prices. But please note that these (or comparable) materials could be picked up at just about any home improvement store. Ditto for the parachute cord from parachutecord.com—you could find it a lot of places, but $54 is cheap for 1000’ of quality cord.

We’ve included links to Lowe’s for the remaining materials. They could be acquired just as easily at any home improvement store.

What it doesn’t include:

Doors (you can usually find used glass doors at places like the Habitat Re-Store or other used building supply stores). You’ll want to buy your doors before you go about framing the walls, since the dimensions will depend on the door.

Hinges, if the doors you buy don’t have them.

Wood Screws, since you’ll probably have some laying around.

Duct Tape. Duh. Especially useful for wrapping around the joint between the bow pole and the post pole, to prevent tearing on the poly. Similarly, for buffering the end of the ridgepole so that it doesn’t tear at the poly.

Good Drill Bit. ¼” for drilling into metal.

AND…Basic tools, including a drill, a heavy mallet, measuring tape, a hacksaw or reciprocating saw to cut the posts (or have the home improvement store do it, as we did), and a plumb line if you’re super anal.

Since Emily and I sowed the inaugural bed of romaine lettuce in March, 2011, hundreds upon hundreds of community members have graced the Duke Campus Farm with their toiling hands and sweating brows and triumphant laughter.  Our workdays, festivals and workshops have attracted students, faculty, media, chefs, out-of-towners, and top-level University administrators.

Through it all, we’ve tried to foster a community space that evokes a modernized version of the Jeffersonian ideal. As Jefferson wrote in 1781, “Those who labor in the earth are the chosen people of God, if ever he had a chosen people, whose breasts he has made his peculiar deposit for substantial and genuine virtue. It is the focus in which he keeps alive that sacred fire, which otherwise might escape from the face of the earth.”

Alas, it seems that while the Duke Community is eager to tap DCF’s deposit of “substantial and genuine virtue”, while they are keen to “keep alive the sacred fire,” while they willingly toil in this little square of paradise on the edge of the Duke Forest, sometimes nature calls them back into her bosom. That is, sometimes they have to pee and poop.

Until recently, Farm staff had few answers to the squeamish pleadings for a place to find relief. We meagerly pointed to the nearby forest in what amounted to an apology more than a solution.

Today, I am pleased to write, we can do a whole lot better. Thanks to Green Grant funding from the Sustainability Office, and the patient work of many hands, the Farm celebrates the opening of its very own outhouse. It is, to quote one user, “certainly the nicest outhouse in Orange County.”

If you’d like to take a virtual tour, Bryan Roth over at the Duke Communications shop has prepared a lovely little video.

Since the outhouse project began, I’ve had a lot of questions about its purpose, design and construction. I’ll try to answer a few common questions here. Feel free to add your own in the comments, and I’ll do my best to respond.

Why build a pit privy instead of a composting toilet or an artificial wetland?

I’ve gotten this question many times, including from one disgruntled reader on Duke Today who expressed her “shock” and “disappointment” that we would build such a primitive structure. The simple answer is that we tried—really tried—to convince Orange County to permit a composting toilet. After all, the Duke Campus Farm strives to minimize our external inputs and, to be blunt, poop can be an excellent and safe source of plant nutrients. We wouldn’t have used the compost (aka “humanure”) on any vegetables, but we could have used it to grow a rainbow of zinnias and sunflowers. Alas, the gods that be in Orange County were having none of it. So much for a progressive county, huh?

As far as artificial wetlands go, I think it’s a great idea. I helped design the artificial wetland that processes the brown water at the Montessori School of Raleigh Middle School in rural Durham County. It’s a lovely system, complete with plant-lined berms, a UV-light and a constructed wetland. It also cost about $100,000 to build, or about 10X the annual operating budget of the Farm. If anyone is looking to cement their legacy, the Farm is happy to offer naming rights for the wetland successor to the outhouse. Email emilysloss@duke.edu.

Why did you build such a nice structure? Isn’t it just a hole in the ground?

Another common question. It’s true that the outhouse cost $1,000 in materials alone, not to mention over $600 in permitting fees and non-negligible labor costs. It has ample space inside, two sliding windows, a Dutch door, and a small library.

The answer is several-fold.

First, I’m out at the Farm a lot. Emily, Sarah, Damon, Anna, and others are out there even more. I want a pleasant place to do my business and I imagine that they do, too. While I’m “busy” I like to watch the deer that mosey on the edge of the Duke Forest, and watch the sunset out the window as I catch up on the latest issue of Mother Jones.

Second, there is a growing perception of farming as a second-class occupation, dirty work, even uncivilized (ironic enough given agriculture’s leading role in the birth of settled society). The Duke Campus Farm exists to, among other things, renew the image of farming as a rewarding, attainable and, yes Mr. Jefferson, virtuous occupation. Even—ahem—for young people with a world-class education. Farmers should not be relegated to a dark cramped putrid bathroom any more than they should not go to the opera or enjoy world-class healthcare.

Finally, the Farm is a center of community. Beauty inspires community. Comfort facilitates community. If we can’t be proud of what we build together, with our hands, we will surely struggle to build something worthy in the intangible dimensions of community space. Or, as Emerson wrote, “I have heard that stiff people lose something of their awkwardness under high ceilings, and in spacious halls…to teach us manners, and abolish hurry.” Indeed.

What qualified you to build this thing in the first place?

Stubborn patience, an abundance of time, and really well-written and specific building plans.