Absolutely. The low hoops should be covered with Agribon or other breathable covering. Set the interior hoops as close to the plant tops without touching the plant (frost). During very cold weather, the fabric can be left in place to maintain the soil temperatures.

Yes I do, only in the winter and to protect from bugs. Also to plant things earlier in the spring, I use Agribon row cover.

Fall planted spinach and lettuce. The row cover was used in this example to keep grasshoppers from eating the young seedlings.
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It is said that for every layer of protection you add to your plants moves you 500 miles south of you. For Example, I am in zone 5. The high tunnel moves me 500 miles south, North Texas. Row cover added inside moves me another 500 miles, South Texas. Usually I add two layers of row cover. We have had temps outside to -11 degrees with wind chill of around -30. I still have Napa Cabbage, Bok Choy, Beets, Carrots, Green Onions, Turnips, Arugula, Spinach and some Lettuce growing. It is really amazing what some plastic and row cover can do!

Jay

For fun we are also trying out a tunnel over a tunnel inside a tunnel.

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Ok, not really. We are building a new tunnel and wanted to put it in the same place as the existing tunnel. I wanted to get it up before the ground froze, so we built over it. We will be taking down the smaller tunnel and moving it to another location on our "farm". Hopefully we can get the plastic up on the new one in the next several weeks.

Jay

OK ... I understand now.

Jay... Keeping GH inside a GH is not as odd as it may seem. That's exactly what i have built and i am growing spinnach, lettuce beets, scallions and peas in my unheated GH. The peas have taken a hit with the -11F we had this week, but i suspect they will come back from the ground when the temps regulate. If it stays about +20F, i should see some new growth.
Lettuce and spinnach are acively growing though slowly. Had my firsh harvest of spinnach early January (Early december sowing) but things have slowed way down with the temps consistently hovering in the single digits and low teens.

i figure i don't need row covers with the GH inside a GH design.

Poppa

I had used a 3 layer approach a few years ago and I took temperature readings to keep track on how tomato plants were doing. My conclusion was that there were too many cold spots- I lost about 20% of the plants. Even with a fan moving air between the midddle layers there were specific areas where the temperature dropped to dangerous levels. The bottom line is that when the temperature drops and stays low for an extended period of time the inside temperature will eventually "approach" the outside temperature unless you add heat.

Now I just heat the whole unit with a woodstove and keep the regular circulation fans going thru the night. Plants are much happier and my costs aren't really that much different.

I am getting closer to being finished. I still need to make the 4 roll-up/pull down doors on the ends, two walk through doors and pull the plastic over the whole thing. It took 8 hours to tear down, 8 hours to set all ground posts (hit a big chunk of concrete!) 20 minutes to put up the hoops, 4-5 hours to attach baseboards and hip boards, 8-10 hours to finish endwalls to this point. I have to do everything, by myself and after school or on the weekend. So if I had help, it would go much faster.

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I hope to get the plastic on in the next 10 days, then I can start taking the other one down and rebuilding it.

Another view.

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How does the heat retention compare between poly sheets and Agribon or other breathable coverings? I really like the pest control the fabric offers and the fact that it would not need to be vented or the sides raised. Just wondering how many layers it would take to equal a poly covering? Would the Agribon keep something as small as spider mites off the eggplant in spring? I can grow eggplant later in the year, but in spring, it is eaten alive by those nasty little critters that I can't even see.

Jrslick, the structure looks impressive. I'm curious as to why you are devoted to that spot over another GH. I would want to avoid the site where crops had been continually grown under plastic that had potentilly had led to higher salt concentrations in the soil.

Before covering, I would go to Home depot, Lowes or other store providing swagged pipe and cross-connectors and attach a few more perlins for support. Two is hardly enough for that size structure.

Buffalo, I think agribon row covers are great but they function somewhat differently than greenhouse plastic. You can usually just prevent frost or gain 5-6 degrees from even Ag30 fabric. Although it would be good to keep insects out you also need to be concerned about diseases and insects hatching from the ground beneath the fabric and with eggplant you will need to uncover to allow pollinators to work. Since row cover fabric will "Breathe" you don't need to ventilate.

A major problem with rowcovers is the need to anchor them with a vengence against windy spring days. Expect tears in the fabric from time to time. My greatest success was by using pins every 6-8' and then laying a sandbag over each pin. If the wind gets under an end you still could be in trouble.

When I purchased the used tunnel, I had intended for it to go between the smaller tunnel and the next one to the east. The problem was I left enough space to build another 18 foot tunnel there, not a 30 foot tunnel. The distance btwn the two was 35 feet. That only left me with 2.5 feet between tunnels, not good for air flow or build up of snow.

Also, I did not have another space that was large enough to put it that was already in production. In order to put this tunnel in a new location, I would have to have done lots of dirt work and that would have added to the cost. I did have a space that I was wanting to build another smaller tunnel on. It was currently in outdoor production, it was level and ready to go. So, I decided to build over the smaller one. I started this project in November and I knew the ground would freeze and I would have had a hard time getting it built if I waited until spring.

So I set all the ground posts, in both locations. Then I have slowly, as weather allowed, finished the big tunnel.

I also have established beds in the small tunnel that I am going to continue to use in the big tunnel. I didn't want to loose these wonderful beds. I have worked hard to build my soil with compost and organic matter.

Last winter this tunnel was uncovered and we had lots of rain and snow. It was very wet. That would help with any salt build up to flush it out. Also about salt build up, I have heard conflicting reports about this. I have heard a lot more that it isn't a problem. In fact one College professor/researcher presenter said he has never seen a salt build up problem in a tunnel.

In addition, I had a few crops still growing in the smaller building that I didn't want to loose.

To answer you question about the purlin. There is another purlin that goes down the center of the building. I was unable to put it on because I would have had to walk down the center of the smaller tunnel or hire someone with a bucket truck to come out and help put it on. Also, I didn't want to remove the inner plastic before the outside one was ready for plastic.

Now, I have the plastic on the big tunnel, I am going to finish the doors on the big one and take the plastic off the smaller one. Then remove the ribs, add the third purlin to the big one, and then remove the rest of the small one and move it to its new location.

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About cross bracing, I was wondering about adding that too, but I have contacted the company, Stuppy's and they said they are engineered to not need them. Also, we don't get the snow that you do in the Northeast, so I am not too worried about it. The person I purchased it from lives one hour away and his location was very similar to mine. Top of hill, no wind break and he never had any problems. So I am trusting the company and the previous owners experience with that aspect. Will I add some cross bracing, maybe, just in case.

Thanks for the questions.

Jay

Good points, Jay. I Have had minor salt issues but tomatoes seem more salt tolerant than cucumbers and basil, the other crops I grow under plastic. I also made the mistake you mentioned of placing two structures too close but this year the pile of snow appears to be melting whereever it comes in contact with the plastic.

Thanks, It took me a while to decide what I was going to do. Basically, I doubled my work load this winter/early spring moving both tunnels. However, it was the only way I was going to be able to achieve my goals.

In fact, the person I bought this tunnel from has another one identical to it. If the time arises that he decides to sell it too, I told him to give me a call and we will work out a deal. If I am to get it, I will probably end up doing the same thing again. Maybe I will move the other tunnel first though! It has been nerve wrecking putting up the hoops, adding purlins, endwalls. Just making sure the plastic doesn't get damaged on either building!

Jay

BTW, the new Johnny's catalog has on its cover likely what the OP was wondering about.

Dan