Are you using row cover too?

no shutters on the exhaust fans? if you have shutters that stay closed then how would shrouds help?

QNo row covers. I used to do that but now I rely on wood heat which usually can be expected to give about 20*F gain. I have string lines up so row cover would be out of the question. I also rely on circulation fans to avoid cold spots which I always got when I used triple cover layers.

Randy, I have shutters but they never close as tightly as I like. That is the only major leakage I can explain. I had laid a post against the shutters to help hold them more tightly closed overnight. I'm considering just using a bungee cord to hold a piece of plastic over the fan protrusion.

The next few nights shouldn't be near as cold but to only get 10*F gain from dry wood and a 160,000 btu stove has me baffled.

Most of my tomatoes are blooming and I don't want catfaced fruits.

I don't think you are losing that much heat through fan shutters. single or double layer of plastic? I would make row cover a priority until all danger of freezing weather is over. If your plants don't survive you won't have to worry about string lines.

Double layer plastic although I don't inflate roll up sides. The sides are wire locked fairly tightly. Ends are my own concoction of framework but I've sealed cracks with foam sealants.

I won't return to row covers in the tunnel. If there ever is a chance of losing plants I will use propane heaters. The last time I used row covers I lost about 10% of the crop. I believe it was 2005 that I constructed a canopy frame tunnel within this 30 x 96 tunnel and then had wire hoops supporting another layer of row cover under that. The main problem is that you can never see what's happening under the covers. I believe there are still pictures of that setup on my website.

Without the stringline support plants would lay on the black plastic and fry.

Folks in the rest of the country are basking in warmth while we're in this weather pattern of cool rain coming off the East coast. I've had stoves cranking out heat day and night for 3 days. Even western PA is 20*F warmer than the central part of the state.

And I'm still not able to get tunnel temps above 60*F.

Heck, I think staying ten degrees above outside temp is excellent. I just assume the high tunnel and greenhouse get to outside temp or within a degree or two. I am happy when it doesn't drop below the outside temp, which is actually possible in precisely the right conditions. I have seen my mine be at least 2-3 degrees below the outside temperature.

Cole, I've seen the graphs of lower inside temps presented by a few researchers. I guess the whole concept of tunnel growing is more complex than we can imagine. One might think that running circulation fans every night only drops the inside temps, which may be true, but that temperature is uniform to all plants. I actually believe that with moving air the plants can survive temps below 32*F.

Greenhouse heater went out last night at two in the morning. Outside temp was 50 degrees, inside greenhouse temp was 46. 4 degrees colder inside than out.

But for how long? When I saw the grafts the temp inside was below outside temp for just a few hours. Usually the difference is less than 4* . It makes me wonder if tunnel growers should be paying more attention to "Growing Degree Hours" like outside growers look at "Growing Degree Days". I had one night when inside temp. was 34*F but I didn't allow it to remain that low for long.

My plants seem to be taking it all in stride and growing fairly well. I even noticed a few forming green fruit on my Favorita cherry tomatoes. That variety seems to thrive under extreme conditions.

Another cool morning- down to 36*F an hour ago and only 45*F in my larger tunnel. I believe there may be poke holes in the outter film layer at the peak, where I can't see them. We had a few gusty storms last summer in which debris was blown against my tunnels. I replaced broken glass in a door and patched a few holes then but I may need to replace film within year.

I've noticed that my HTs overnight lows are warmer than outside during two specific times of the year - early spring (now) and late fall. In both cases, it's because there is bare ground not covered with plastic and plenty of soil moisture compared to outdoors. The soil temperature inside the HT also averages much higher than outside. During the summer and early fall, the HTs run at the same temperature at night or even slightly cooler on some clear nights. This is because a dense vegetation canopy radiates heat quickly and cools well below ambient, and the soil temperatures inside the HT tend to be cooler than outside due to the perpetual shading.

Wish I could say that my spring inside temps are staying a lot higher. Over the next 3 nights with temps expected to drop to 32*F each night I know I'll need propane backups. My take is that by covering every sq. ft. of soil surface that I can retain soil heat generated when solar heat is trapped. It could be that the black plastic prevents that soil heat from escaping but I tend to doubt that trapped soil heat is significant at 3:00 A.M. I'm more worried that as many plants are approaching waist height the newest blossoms are further from the warm soil but then heat rises, doesn't it?

Yep, the plastic definitely prevents heat (and water vapor) from escaping. On a clear, calm night, air over plastic or grass/vegetation cools off much more than over bare soil. It's kind of a trade-off between keeping the soil warm and keeping the air warm at night. For this reason, I prefer to not lay plastic until most risk of frost has passed.

You mentioned losing 10% of your tomatoes last year because of row cover hiding issues. May I know what happened?

Okra, that wasn't last year but ten years ago in 2005. When I constructed a canopy tunnel within my 30 x 96' high tunnel and then put row cover over and under that canopy. The row cover under was supported by wire hoops and I also had about 50 gal. Jugs full of water placed around plants; BUT NO SUPPLEMENTAL HEAT. The majority of the plants lost were along the edges and ends of the rows. I believe that cold spots developed when temps dropped below freezing.

It's 37*F now at noon and snowing so I'm grateful to have wood heat to keep plants growing. And here's my secret that I will reveal- You can keep plants alive under most conditions with just row cover but if you want then to GROW you need to keep them warmer at night ( and some days).

That's good to know. I was planning on experimenting with some early tomatoes under row cover this year (no supplemental heat). However, we can get hard frost until late May.

You might be fine if you use a heavier cover or even double-up on the cover for those frosty nights if most nights are warmer. The problem is that if the weather stays cooler your efforts of planting and caring for those plants put out a month early will only be a two week earlier harvest, hardly worth the hastle.

One other possibility of a bad outcome is our weather forecast for tonight- 28*F and gusty winds. I've had this type of weather in the Fall with Agribon 50 and if it doesn't blow off the rows and tear the cold air still penetrates the fabric and the crop is toast. A much better forecast is calm, clear and frost.

Even within my high tunnel last night the temps were steadily dropping until I lit the second propane heater to complement the wood stove. Outside water buckets had 1\4" thick ice this morning so I was hoping that I could keep inside temps above 50*F.

Barrie2m, how did you fix your problem, I am getting ready to invest in a high tunnel.

I need to keep my tunnel above 50 F all the time, 13F has been the lowest temp. in the last 30 years in South Carolina, that is a 37 degree differents. So I need to trap 40 degree from the sun & use gas heat ass a back up. Any Ideals for me.