Inexpensive Hoophouse

I took a 7 foot section of 1/2 inch metal electrical conduit and hammered it into the ground 2 feet. Then I just slid 3/4 inch pvc electrical conduit over the metal to make hoops. 4mil painters plastic for the skin. $70 and less than 2 hours of work for a greenhouse that is 20 feet long by 7 feet wide. I'm not quite sure it will survive the snow.

Will it be heated? Perhaps heat would melt it off. If not, just be diligent to knock the snow off everyday. What about bending cattle panels over your pipe then putting the plastic on top of that? A 4x16 cattle panel is about $25 or so.

You put a pretty tall arch, it has a good chance of shedding snow. You will need to be diligent about venting, you can cook your greens really easy. Easy to get an extra 80 degrees inside if it is clear and calm.

Painter's plastic is, at best, translucent. My SWAG (Scientific Wild Assed Guess) says you are losing 25-35% of the light, compared to less than 10% loss with UV stabilized greenhouse plastic.

Some plants will do fine with that, and may even prefer the more diffuse/reduced light. But the light lovers will languish.

The UV stabilized stuff typically lasts 4-6 years, while the non-UV stabilized stuff will rarely last the 2nd season.


Maybe you only need it for 6 weeks in the spring...

There is no wrong way, only different ways.

Surely the test will be a good winter storm....wind, freezing ice, followed by a snow cover.

The first thing I'd question is the amount of weight that is holding the edges down to the ground. A stiff wind laughs at bricks. I tried bricks and cement blocks and it failed. I ended up using battens that I wrapped the ends of the plastic sheeting around then nailed it to a 20' 2x4. I drove rebar into the ground and secured the 2x4 to that. That worked. A neighbor used dozens of old discarded car batteries to hold his hoophouse plastic down and it failed in a windstorm. He ended up doing the 2x4 thing and then using the car batteries to hold the 2x4 in place. That worked. The problem is that if the wind gets inside the hoop house at all and changes the air pressure between the inside and the outside, the plastic simply whips off unless strongly secured.

I don't recall how long standard plastic sheeting lasted me in NJ. I think about a year or so. Here in Hawaii it lasts exactly 9 months, then splits along on the fold seams. Greenhouse plastic is UV resistant and is rated at varying lengths of time. The plastic my neighbor put onto his greenhouse has lasted 6 years so far and appears ok still. His is really taut, so there is no flapping.

You can put rebar inside the pvc to strengthen the hoops. If you are expecting a fair amount of snow, you will still need some internal bracing. A common way of doing this is to use a wooden frame that both braces the hoops and provides support for climbing plants. You can build either a box frame or a t-bar. Wire or cable is strung through the cross pieces at regular intervals to tie string to.

Cattle panel would strengthen the hoops, but it would shred the plastic.

I second the comment about greenhouse plastic. Painter's plastic is not designed to last for more than a few weeks and even heavier vapor barrier is not designed to withstand UV. Still, it may be worth the risk to keep things cheap. This is not a life or death scenario, I assume?

No heat is planned and I'm just growing cold loving stuff like kale and spinach, radish, and carrots. I might add a rocket heater modification, we will see.

The painters plastic is really just cheap practice material - if it holds up to the weather, I'll get the good greenhouse plastic. If it gets crushed by the weather I don't loose much.

I do worry about the bricks being able to withstand the wind. I added some makeshift sandbags too and I might add more of those.

Thank you all for the very helpful comments! The plants are loving greenhouse!

Jimbo

This is a pretty nifty (I am not showing my age!) setup. I like the suggestions that Jeff Higdon and Su Ba gave for reinforcing the structure and keeping the plastic tied down.
You could even use chicken wire, as it is more malleable for your form than cattle panels are, to support your plastic.
I have had the same issue that Su talked about with wind ripping off tarps and plastic sheeting until I used the trick with the 2x4 and anchored it.

the trick to wind resistance, is to reduce 'billow', that is movement of the plastic. I spent a couple of years under a tarp (roof was gone) and once the wind starts picking up the covering, every little bit of motion adds to the problem. Use clips, tautness and tie downs to keep the covering from moving. Think about a sail or a wing, wind acts the same way, lifting and pulling at the surface from the outside. watch for when the covering swells or collapses and pull it tight to keep that motion to a minimum.

I lived with tarp on our roof for nearly a year. I lost the first tarp to billowing. The next one, I put nails in every foot or so around the perimeter of the roof and then wove a net of nylon twine. It kept the waves from developing and ripping the plastic. I don't know how something similar would work with greenhouse plastic. I would be concerned about wearing holes in it. I think inflating two layers may be the best answer.

I am going to be using a layer of chicken wire over the plastic of my Chicken Hoop Tractor. It has a base of cattle panels, the tarp and plastic (for light) and then the chicken wire on top to keep it from billowing. I will be using a 2x4 structure to maintain the hoop structure under snow or wind load.

We have similar low tunnel hoops. We use UV-stabilized plastic, because other plastic starts cracking and turning into chips within a couple of months in our high-altitude sun. Our location is very windy and the best method we have found is digging a trench alongside both edges, laying the extra foot or two of flap of plastic in the trench, and filling it in. We don't have any serious snow load here because it's a desert, so I can't help you with that. Ours is similar to yours, but the materials are little different: we have a long waste metal pipe lying on the ground along the bottom of both sides, with holes drilled to hold willow wands that we tie together to form the hoops.

We just had a major snow storm for Northern Virginia. Over a foot of snow and my cheapo greenhouse survived! Unbelievable! Rocket Mass heater modification coming next.


Jimbo