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This winter’s “high tunnel” experiment begins

October 24, 2011

We’ve had something fresh to harvest & eat from the garden continuously during each of the last 12 months; last fall’s garden transitioned into a moderately successful winter garden thanks to the cover I provided during the cold stretches.  My experiment last year was to cover three beds individually with contractor’s plastic using pvc ribs; the “hoop-house” posts are here and a sample picture o the first one is below:

Technically the structures were more “low tunnels” than hoop houses.  They worked OK but all the covering, uncovering, and maintaining supplementary heat(shop lights) in each was a lot of work.

This year my scheme is to try and cover all 3 beds with one structure and then set up an automatic venting mechanism to reduce the hassle of temperature control.  I may set up supplementary heat of some sort if time and cheap-arsed ingenuity permit.

The 1/2″ pvc used in the low tunnels last year won’t suffice as it isn’t rigid enough.  After investigating all sorts of materials for the ribs I decided that 1″ PVC would suffice if cross bracing was utilized.  I played with pi to try and figure out the minimum width of greenhouse overwintering plastic I needed to order and ended up with a calculated 24′ as my width.  Basically I needed to know what the length of the arch would be when straightened out; it had to be long enough to not only cover all three beds (min footprint of 15 ft) but also “bowed” enough to provide sufficient height.

The height is important for several reasons-

  • I will need sufficient headroom to accommodate a relatively short gardener (me) while working in the structure.
  • More headroom equals more slope for better water/snow shedding.
  • More headroom = more volume = more consistent temperature control for the entire setup.

The 24′ lengths of pvc gave a good 7′ of headroom in the center and plenty of room down each “aisle” between the beds. I will space them 4′ or 5’apart (6 or 5 ribs) and will end up with a roughly 20′ x 15′ floor area.

I ran a 1/2″ spur from the main well line down to the area of these beds so that the irrigation control box (actually just an underground faucet box for now) will be inside the structure.  This will be convenient for both watering and freeze prevention.

The 1″ pvc fits perfectly inside 1 1/4″; I opted to make sleeves out of the 1 1/4″ pipe vs actually joining and gluing the 1″.  This allows for easier storage (can be disassembled and stashed in maximum 10′ sections for the summer) and the ability to more easily change to “plan B” should plan “A” not be as functional as I am hoping for.  (There is no plan B yet; I’ll have to regroup and come up with something if this scheme doesn’t work.

The 1 1/4″ sleeves are 6″ long and I pre-drilled two set screw holes into each one.  The screws are very short self tapping machine screws I happened to have in my shop.  Once assembled, the joints look like this:

I put 3 ribs up today for evaluation and they seem to be rigid enough.  I also wanted to get the perspective on what sort of profile I would see when this structure is complete. It is less obtrusive than I was expecting, especially from outside the fence.

The view from the rear:

More to follow as I piece this together….

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5 Comments leave one →
  1. October 24, 2011 8:12 am

    I will be putting a couple beds under cover this year. I don’t plan on having all that much to harvest, mainly greens. I’ll have low tunnels covering just the individual beds. What type of plastic did you use last year? Will you be using the same this year?

    Great idea with the PVC over the 2 beds. I may have to steal this idea in the future. Since my beds are laid out in a grid, I should be able to do it the same way. For the sleeves, did you consider something other than screws? They could strip out. Granted, by that time, the PVC may be damaged by the UV light.

    Anyway, keep us posted on the progress.

    • October 24, 2011 9:23 am

      The screws shouldn’t be a problem- they just keep the 1″ from sliding out when setting up. Once bent it is very difficult to pull out of the sleeve without the screws.
      The 4 mill plastic from Home depot that is 12′ wide is what I used last year. The 1/2 inch pvc was cut by approx 1 foot for the 4 ft wide beds.

  2. October 24, 2011 9:06 am

    How are you anchoring the ends of the hoops to the ground?

    • October 24, 2011 9:26 am

      The north end will be plastic on a wood frame with a door. The south end will be all plastic. Inside I will cross brace with paracord I think.

Trackbacks

  1. The bigger polytunnel/hoophouse project, post #2 « Behind cohutt's fence

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