How I Built and Use My Cattle Panel Poly Tunnel

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I built my poly tunnel from cattle panels, and it has been one of the more useful experiments on the homestead. I used 16-foot cattle panels and arched them across a 12-foot span because that is what my space allowed. If I had more room, I may have gone closer to a 14-foot span because it would give a little more growing width while still leaving plenty of headroom. The tradeoff is that a wider span lowers the center height.

The 12-foot span worked well for my bed layout. A person can usually reach comfortably into a 32-inch bed when there is access from both sides. With 24-inch walkways, the layout works out like this: 32-inch bed, 24-inch walkway, 32-inch bed, 24-inch walkway, 32-inch bed. That equals 144 inches, or 12 feet. In real life, I would still leave a little room for posts, side rails, plant growth, straw bale insulation and general working space. This simple layout worked out well.

With the 12-foot span and roughly 5-foot side walls, the center height is close to 9.5 to 10 feet, depending on how the panel bends and where it is fastened. With the same side wall height, a 14-foot span would be closer to an 8-foot center height. That would still be enough headroom and would give a little more floor or straw bale space.

There are several ways to build a cattle panel poly tunnel, and some are much more permanent than others. Mine was built as a one-man, lower-cost experiment, not as a finished commercial greenhouse where I arched the panels from one side to the other. Another way would be to run the panels lengthwise with a pitched roof. In the design, the north wall can be more solid, act as an insulator and a wind break. I have seen people use straw bales along the north wall for insulation, water barrels with aquarium heaters or solid construction with insulation.

For my first build, I used 7-foot T-posts so I could get about 5 feet of side wall height. I placed 1 1/4-inch PVC tees on top of the posts, then ran 3/4-inch EMT conduit through those tees as the side rail. The ends of the cattle panels were then wired to the EMT with wire bag ties.

One thing I would change on my next build is post spacing. I did not place the posts as close together as I should have. Next time I will use about 5 feet as my minimum spacing between posts for better support.

Once the four corners were squared and set, I ran string from post to post so I could keep the line straight and the height consistent as each post went in. This kept everything in line and level. We used landscape timber for the end wall framing.

For the covering, I put shade cloth over the cattle panels first. That gave me a buffer between the wire and the plastic so the panel edges were not rubbing directly on the plastic. Then I covered the tunnel with plastic. After that, I put bird netting over the plastic to help hold it down and reduce wind movement. We get 40 mph winds fairly often, and that setup held up better than I expected. We used 2” web banding across the top every 8' when we built the local master gardeners’ greenhouse. I used some banding on the end walls to keep plastic tight around edges and doorway.

I placed the tunnel on contour because that fit the land. The ends are mostly north to south, where north to south end orientation would be my preferred direction even on flatter ground. This gives me optimum light and decent airflow.

Once danger of frost passed, I pulled the covering off. In warm weather I let the tomatoes grow up and through the 4-inch squares of the cattle panels, so the tunnel frame becomes a trellis. That has worked well, although it also means I have to place the plastic back on in autumn.

I am still debating whether I want to pull the plastic on and off each year. If I remove it after frost season, I can use a cheaper grade of plastic and replace it every few years. If I leave it on year-round, I will want better greenhouse plastic because the sun will break down cheaper plastic faster.

So far, I like the design enough that I plan to build a second one this fall. I have less than $500 in the first one, and for a learning build, it has been a success.

The growing side has been as much of a learning curve as the building side. I was new to poly tunnel gardening last year, and I will definitely plant some things differently next season. My goal is to grow year-round, but that will bring both opportunities and challenges. From mid-December to mid-February, I expect that to be my slowest season. I will likely have root crops and cold season crops in the ground, but I am not expecting fast growth during the darkest part of the year.

This fall, one of my experiments is to see how long I can keep indeterminate tomatoes going. Soil temperature, daylight, and air temperature will all play a role. Lights are easier to add than warm soil, so ground temperature may end up being the main limiting factor.

I also built two rows of EMT framing inside the tunnel, one on each side of what will be the center 32" bed. This provides structural support and will allow me to make smaller plastic-covered sections inside the bigger tunnel for early crops. It is basically a tunnel inside a tunnel, similar to having winter cold frames inside the larger structure.

On those nights when it gets cold but the days warm up fast, typically February into April, I use a small RV diesel heater just to keep the chill off in the early morning. I am not trying to keep the cold frames warm, just trying to keep the growing area above about 40°F, which is enough for crops like lettuce. I exhaust the heater into the main tunnel where there is plenty of air leakage but also works to keep the main space above freezing as well; the clean hot air is vented into the cold frames.

The biggest lesson for me is that a tunnel is not just a structure. It becomes a microclimate that must be managed. It can protect crops from frost, wind, and hard weather, but it can also heat up quickly, hold too much humidity, or dry the soil faster than expected. The frame is only the beginning. The real skill I am learning is how the air, soil, water, light, and plants behave inside it.

Has anyone else built a low-cost tunnel or used a smaller tunnel inside a larger one for winter crops?

Here are a few pictures although the tomatoes are covering most... I'll get some clearer pics this fall.

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How I Built and Use My Cattle Panel Poly Tunnel