Greenhouse Kit - build a low tunnel
Are you considering a greenhouse kit to save yourself some time and effort? Well, here's a story of a 14 by 20 foot low tunnel greenhouse that neighbors of mine built from a kit. It is a nice design and appears to be very effective.
If your plan for frugal living includes greenhouse vegetables, but you don't want to fabricate something yourself, a kit may be the answer. You still have to put it together, but you don't have to fabricate anything, so it can save you some time and effort.
Let's meet Catherine and Martin Wissner, some really nice folks that live just a bit southeast of Cheyenne. They raise sheep, turkeys, llamas and lots of vegetables. They have a low tunnel and a high tunnel, and plenty of open air garden space where they have quite a bounty.
For two people, their operation is very impressive indeed. I get tired just thinking about all they have going. They were kind enough to invite me out to their nice comfortable place in the country where the large shade trees remind me of the traditional homestead farm.
The greenhouses remind me of their eye toward technology to help create self-sufficiency, and that's a good way to be.
Let's look at their low tunnel which is really a greenhouse by any other name. I suppose the difference is more in the connotation of the word "greenhouse". It usually suggests all the vents and fans and humidity controls of a gardening structure.
The Wissners deliberately stayed away from all of that to reduce costs and keep it simple. A good idea if you ask me. Vents and fans are expensive to buy and can be a considerable expense to operate. Heaters can too. When someone rolls their eyes when talking about heating their greenhouse with propane, you don't have to ask them for more information - you've got the picture of great big dollar signs.
This low tunnel greenhouse kit is of a hoop house design as shown on the left, and it's about 9 feet tall in the center.
It is simply multiple sets of rigid metal pipes bent in an arch that make the ribs (rafters or bows) for the structure. Think of a rib cage, and you have a good idea of why it has that shape and just how strong it is.
Each rib of the greenhouse kit consists of three separate pipes. The pipes are fastened together with heavy duty sheet metal screws. There is a ridge piece running down the center of the upper most portion of the structure, and two purlins on each side.
The lower purlins are made from 2 by 4s about 4 feet off the ground on each side of the structure. Carriage bolts hold the purlins to the "ribs".
The ridge piece is connected to the "ribs" with a special fastener that bands the pipes in place without the need to drill holes.
The pipes for this greenhouse kit are 14 gauge, and that means they are very rigid and strong. You won't be bending these accidentally. The ribs are spaced 4 feet apart.
Note: a spacing of 4 feet is typical for a greenhouse kit. You can add more ribs if you like and create closer spacing between ribs or a longer low tunnel than what the regular greenhouse kit will normally provide.
The covering for the low tunnel is a double layer of clear poly film with a blower used to inflate between the layers for added insulation. The blower, shown on the right, takes in air from outside through a flexible tube and blows it between the two layers of poly.
"Wiggle wire" is used to secure the double layers of poly to the end pieces. The "wiggle wire" uses a metal channel into which the plastic covering is inserted. The wire is then placed inside the channel and it presses the plastic against the inside of the channel to hold it in place.
The photo below shows the "wiggle wire" used to hold the poly covering in place along the bottom edge of the purlin. It is also used to hold the edges of the poly in place at the ends of the structure.
For this greenhouse kit, the Wissners selected ends made from twin wall polycarbonate panels with square metal tubing and metal channels to hold it in place. The panels are rigid and transmit light very well.
The photo to the right shows how the upright members of the end walls are connected to the "ribs" at the far ends of the structure. Also note how the metal purlin is attached to the end walls by clamping onto the "ribs" at the far ends of the structure.
Note: this structure is made with 4 purlins and a ridge piece. Two wooden purlins are located about 4 feet off the ground, a metal ridge piece is in the top center of the building, and two metal purlins are located one on each side about midway between the wooden purlin and the ridge piece.
A mechanism that rolls up the sides is attached to both sides of the low tunnel to allow the sides to roll up for ventilation. It is amazing how the mechanism rolls up the sides with ease.
The covering is secured on the underside of the purlins with "wiggle wire". This makes the upper shell of the covering immobile, but allows the lower portions to hang down to the ground but not secured to the building.
The portion that hangs from the purlin to the ground is attached on the far end to a long pipe. The pipe is attached to the roll up mechanism so it can be used to roll up the clear cover.
Nylon rope is woven from the purlin to the ground in a zig zag pattern to provide a type of "net" to help keep the loose portion of the clear covering from flapping around when it is in the rolled down position. A flapping portion of the poly cover will soon wear out and fail.
The photo to the right shows the nylon rope "net" that retains the rolling portion of the cover. Here the side is rolled up partway to allow for ventilation.
Ground posts are used to position the ribs in place, and then each rib is secured to the ground post with a fastener. The sides and ends of the structure that touch the ground are wood, and "high sides" are anchored to the "ribs" and ground stakes as shown in the photo lower left.
Earth anchors are used to pull the structure down onto its ground post foundation using turnbuckles. The earth anchor is simply a long metal rod with a auger tip that buries itself in the ground when it is twisted in a clockwise manner. Once in place, the only practical way to get it back out is to untwist in a counterclockwise manner.
In the photo to the left, just the "eye" of the earth anchor is shown above ground level. The rest of the anchor is buried securely underground.
The photo to the lower right shows an example earth anchor. The larger and taller the structure, the deeper the earth anchor should go. The low tunnel required 2 foot long earth anchors, one on each of the ends of the ribs.
Martin built an adapter to fit into a powerful drill, and he used that to install the anchors. Installing the first one by hand with a metal rod was sufficient to motivate him to build a special tool to do the job with much greater ease.
With 12 anchors to install, the custom made tool and heavy duty drill were real labor savers. In addition, it allowed him to work in tight spaces once the ribs and side walls were in place.
Speaking of labor, the Wissners employed several laborers from a local labor shop to help assemble their greenhouse kit. Having extra hands is a big benefit when you are assembling something like this. With one hand holding this and one hand holding that, one can run out of hands quickly.
Having at least two others help you during assembly is a real benefit. One more wouldn't hurt either, even if they only help with getting tools and fasteners for others.
Multiple sets of hands are a must if your greenhouse kit assembly is going to be a pleasant experience.
I should note that items such as turnbuckles, earth anchors and wooden purlins and wooden high sides typically do not come as part of the greenhouse kit. You'll need to purchase things like this separately.
By the looks of the results shown on the left, the low tunnel greenhouse kit has earned its keep. If only I knew how to make Chiles Rellenos, I might have stuffed a few of those beauties in my camera bag.
So, there you have it. A low tunnel that comes as a greenhouse kit with double poly covering, twin wall ends and roll up sides. No electricity, nothing automatic, but good simplicity that works well to provide great results.
Consider something like this as part of your frugal living plan for fresh and inexpensive vegetables. It will last for many years, and you can probably build it in a couple of days with a little help.
Done with Greenhouse Kit, take me back to Build Your Own Greenhouse