tomato frost damage in new high tunnel

Hi Folks,
Yesterday I worked next to a couple of women putting a high tunnel over existing tomato plants.  Well established plants, loaded with fruit, as a good tomato plant is this time of year.

The framework is cattle panels curved over, anchored on the ends, the panels joined side to side.  The whole thing is 30feet long and 10 feet wide, and 7 feet high at the top of the arc.

They covered it with heavy duty visquine, the kind designed for greenhouses.  On the lower 3 feet on one side, row cover was used.

Ends were covered in visquine anchored with straw bales.

Nowhere was the plastic resting on the tomato plants

The next morning, the tomatoes showed extensive "frost" damage.  Disappointing, even heartbreaking for my 70+ year old friend

What can anyone suggest about this situation?

How cold did it get last night?  I'm not sure how much temp protection a single layer hoop provides but I doubt it's more than 10F...

I am not sure exactly how cold, but certainly it was not colder than 30 degrees.

I just heard back from my friend, official temp was 34, thermometer outside her door was 37 this morning.

More remarkable, her uncovered tomatoes did not freeze or suffer any frost damage!

It is quite a puzzle to me!

you need a heat source or a heat sink to retain heat from the day to keep the inside above freezing.
i have seen where people use 55 gallon drums painted black and filled with water in green house/ high tunnel, to soak up heat from daytime sun
i especially like the RMH hot house set up. that can get you through the entire winter, growing stuff in a high tunnel

Polly tunnels are fairly commonly COLDER than the outside air on clear nights. It's to do with air movement i.e there isn't any in the tunnel so there is no mixing of colder and warmer air. The polytunnel cools to the temperature that would be present if there was no wind.

A single skin tunnel will give 1-2C protection in general but that is it. a double will not give much more, they are not designed to stay warm at night without heating. The main use of a tunnel in my climate is to up the temperature during the day to one high enough for plants to grow, at night it drops back down to ambient.

great information!  I thought the warm earth under the tomatoes this time of year would sustain the temperature...

But what can you say about the fact that the temperature did not go down to freezing outside the tunnel... with unprotected tomatoes not getting frosted when the ones in the tunnel did.

that is strange that the ones that froze were under plastic
i dont even begin to understand why
very sad that you lost all those tomatos after all the work involved in putting up hoop structure

Well, it is a mystery to ponder for now.  I think maybe the air movement outside kept those tomatoes warm, but the stagnant air inside the hoop was colder.

Other elements of the puzzle: 6000 feet elevation, at the bottom of a small valley with a side drainage coming down off the 10,000 feet mesa to the south.  It was a clear night.  The night before, there was some frost damage on some of the squash plants, no frost damage on the tomatoes and peppers, though the temperature went down to 29 or 30.

The next night after they had constructed the high tunnel, they covered the peppers and squash with row covers,and they too sustained significant frost damage.

I guess I will ask some of the people around here with high tunnels if they heat them, and for their experiences and opinions.  

I agree about the covers perhaps preventing air movement and creating frost pockets.

Was the row cover on both sides or just one side?  If on one side, was it the uphill side?

It's very common for temperatures inside unheated greenhouses to be colder than outside on clear nights. This is due to radiant cooling. The glazing is exposed to the cold of space.  Just as a greenhouse traps and concentrates  radiant heat during the day, it also traps and concentrates radiant cooling on clear nights.

Radiant cooling at my place, on clear nights, in an open field is about -8 degrees F, therefore, if ambient air temperatures are 40 F, I expect frost in my open fields. I haven't measured it in my greenhouse. My standard practice is that if outside temperatures are below about 45 at night, I'm heating the greenhouse if it contains frost tender plants.

Thanks for a wealth of experience information and opinions.  I knew the community would be a resource!

I am going to go find the hoop house thread, see what they are saying.  Maybe I should have posted there but I didn't think of it.