11.8.2013 Low Tunnels

Over the last week, the weather weanies have been wetting their pants about the possibility of a major winter storm in the mid-Atlantic next week.  As of right now, they’ve called off snow (and probably the rain too.  We’re getting droughty again.)  But they all agree it’s going to get very cold.  Lows in the 20’s and highs in the 40’s.  That sort of cold would probably spell an end to my lettuce, probably the broccoli and celery too.

Since the stuff in my new hoop house has only had two weeks of growth and is not harvestable yet, I would really like to keep my three rows of lettuces, kale, broccoli, cabbage and celery from freezing.  So I built little hoop houses to shelter my three rows of winter garden.  They are made from PVC, rebar, zip ties, duct tape and inexpensive plastic sheeting.

The last time I tried this, I looped 10’ lengths of PVC over two rows in the garden, spanning about 6.5 feet.  The PVC was stuck onto 12” lengths of rebar which I had pounded into the ground.  Originally, I had this covered with Agribon secured with clamps .  The wind tore the Agribon to shreds.  So I replaced the Agribon with plastic sheeting and added 3 strings tied across the top to hold up the plastic between the arches.   That structure ended in disaster.  The rebar wasn’t long enough and the three strings served to make nice bowls in which to collect rain water.  The rain pulled the whole thing down.  It wasn’t pretty.

This was my original low tunnel built in 2011. Bricks and old fence posts weren’t enough to secure the plastic against the wind. String down the center wasn’t strong enough to support the weight of rain water. It all ended in a nasty collapse.

This time, I cut the PVC into two, giving me 5’ lengths which I secured onto 18” lengths of rebar.  Let me tell you now, half inch PVC and half inch rebar are a recipe for severe upper body muscle strain and pure torture on the hands.  Use ¾ inch PVC over 1/2” rebar.  Much easier to get the whole thing together.  Then zip tie more PVC to the center of each bow to form a ridge line or purlin.  Note: gray electrical conduit is better suited for this than regular white PVC for the simple reason electrical conduit comes with a flanged end making it easy to join sections  for the purlin.  With the white PVC, you’ll have to buy connecters.  The duct tape covers the end of each purlin to smooth the surface for the plastic covering.

5 foot lengths of PVC arced over my 30" beds gives enough headroom for all my plants, but I really do wish I had planted more toward the center of the row.  I am having to tuck leaves under the plastic near the edges.  The broccoli doesn't mind a little rearranging but the chard is taking a bit of a beating with all the ups and downs of the plastic covering.

5 foot lengths of PVC arced over my 30″ beds gives enough headroom for all my plants, but I really do wish I had planted more toward the center of the row. I am having to tuck leaves under the plastic near the edges. The broccoli doesn’t mind a little rearranging but the chard is taking a bit of a beating with all the ups and downs of the plastic covering. On the far right, you can see where I used white PVC.  It’s 1/2 inch PVC and as you can see, it will not slide down onto the 1/2″ rebar.  The electric conduit on the left and in the center is still sitting a little high on the rebar in this picture, but in these two rows I used 3/4″ inch PVC and it happily slid right down to the ground over the rebar once it had set in the arcs overnight. The center purlins weren’t installed when I took this picture.

I covered the whole thing in plastic sheeting I had on hand.  I happened to have enough 6 mil (not greenhouse grade) to cover two rows.  My third row is currently covered with a 2 mil plastic.

To keep the plastic on, I have two binder clips on each end of the rows, plus a third clamping down all the loose ends.  Then I ran baling twine back and forth over the top, securing it to the rebar (sort of like lacing a shoe).  During the day, I gently shove the plastic up from the ground, using the tension of the baling twine plus a few more binder clips to keep the sides up.  This allows enough ventilation on sunny days so the veggies don’t cook.  At night, I release the binders and slide the plastic down to the ground.

These smaller structures are much more stable than my first low tunnel and hopefully, they will stand up to wind, rain and snow.  I think they will.

So far, these low tunnels are working just great.  We got down to 26 last night and I didn’t lose a thing.  But I have to say, when viewed all together, it looks like my barn has had babies.

So far, these low tunnels are working just great. We got down to 26 last night and I didn’t lose a thing. But I have to say, when viewed all together, it looks like my barn has had babies.


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