Sunday, 2013-02-10
Quick-hoops are made from 1/2-inch EMT bent into a semi-circle. If you push both ends 6-8 inches into the ground, you get a low tunnel which spans six feet wide and stands about 30" tall. Covered with row cover fabric and 6-mil greenhouse plastic, these tunnels will stand up to a snow load (we have had them completely buried, so you almost couldn't tell there was anything under the snow).
Quick-hoops give you much of the season-extension ability of a high tunnel at about 10% of the cost. This winter has been particularly bad for growing, as it was relatively warm all winter and then we got a sudden cold snap of about -17 Fahrenheit, which didn't allow the spinach to acclimate, so you can see that it has been significantly frost burned, but it has survived and will regrow.
One major downside is that once the snow flies, it melts and freezes the row cover and plastic to the ground, sealing it shut all winter. But if you add 15" ground posts made from 3/4" EMT (adding about 12" to the height of the tunnel), they become tall enough that you can get inside on hands and knees to harvest during the winter, if you just keep one end of the tunnel clear of snow and ice.
One trouble with getting started with quick hoops, especially for the home gardener, is that you have to spend $60-ish on a hoop bender, which might be more than you would spend on a tunnel for a small family. I have designed and built a form on which to bend quick-hoops which uses only a half sheet of 5/8" plywood. It is built in two pieces, so it is small enough to store and transport easily. It also allows you to bend the whole hoop at once, so you don't have to worry about aligning multiple bends or having twisted hoops.
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Take a half sheet (four-foot square) of 5/8-inch plywood. Draw a diagonal from the top left corner to the bottom right corner. Measuring along the diagonal from the top left corner, make marks at 15 inches, 40.5 inches, and 45.5 inches. Take a three foot length of string and tie a small loop in one end. Place a nail or screw at the 15 inch mark, slip the loop over it, and stretch the string along the diagonal. Use a permanent marker to mark the string at the 40.5 and 45.5 inch marks. |
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About 7 inches left from the top right corner, measure 7-3/4 inches down and make a mark. About 7 inches up from the bottom left corner, measure 13-1/2 inches right and make a mark. |
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Stretch the string out and put a pencil at the longer mark. Pinch the string between your fingers and the pencil and use it to draw the outer arc from one mark to the other. When you get to each end, draw a straight line down the string to the inner radius. |
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Then pinch the string between the pencil and your fingers at the shorter mark and draw the inside radius. |
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Now for the larger piece: remove the screw or nail, measure 24 inches along the diagonal (from the top left corner) and place it there. A couple inches left from the top right corner, measure 7-5/16 inches down and make a mark. About 4 inches up from the bottom left corner, measure 3-3/8" right and make a mark. |
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Again, use the string and a pencil to draw the outer arc and the end lines, then the inner arc. |
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Remove your nail or screw and rotate the plywood 180 degrees so we can draw the other two pieces. |
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Let's draw all the marks for both pieces at once. So measure 15 and 24 inches along the diagonal from the (new) top-left corner). A couple inches left from the top right corner, measure 7-15/16 inches down and make a mark. Then move left a bit, measure 7-3/4 inches down and make another mark. At the bottom right corner, go up about 4 inches, then measure right 3-3/8 inches and make a mark. Move up a bit, measure 13-1/2 inches right and make the second mark. |
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Place the nail at each center and draw both pieces. |
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Now we're ready to cut the pieces. The outside edges (the red lines) need to be cut with your jigsaw blade angled in at 30 degrees toward the inside of the curve (so the bottom is narrower than the top). Be especially careful cutting these, as the angle seems to magnify inaccuracies and you want the pieces to match reasonably well. All the other lines will be cut with the blade set square as usual. |
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Then the pieces get glued together in pairs. Each small piece gets glued to a large piece so that the angled cuts form a V-shaped groove for the tubing to set in when we bend hoops. You want to align the pieces so the V is as nice as possible; it doesn't matter if the inside edges don't line up. Use plenty of glue, as this will be under a fair amount of stress. Be sure to glue them so that both pieces look exactly the same! If they are mirror images (with the short piece at the left end on one piece and the right end on the other) then they won't fit together.
Once they are glued, fit the two pieces together. You may need to trim the long ends so they fit together nicely (I did). Clamp them together and drill four holes for machine screws and pronged tee nuts. You probably want to glue the tee nuts in so they can't fall out. You may also want to polyurethane or paint the pieces for protection from moisture...
Then you need a loop of something to hold one end of the tubing while you bend it. I took a (1-1/2 inch?) pipe strap, bent the ends straight, and screwed it onto the end of one piece. You could also use the flexible pipe strapping which comes in small rolls.
