Lettuce wont do well in a GH unless you can keep the temps down. As for the toms, some can take a lot more heat than others. I found that neither of these plants thrive in a GH.

Below 70-75 for lettuce. Toms can tolerate up to low 90s in vegetative stage but once they start flowering, try to keep them in 70s and low 80s. In your zone, you could probably use the GH to grow eggplant and do the toms and rest outdoors. Assuming you like eggplant...

We get a jump start on warm-weather veggies like tomatoes, cukes, eggplants, peppers, squash by transplanting them in our extra GH on May 1 (Zone 5) Even late-April/Early May the temps can get quite hot in the GH if you don't ventilate. And as someone stated if it's too hot flowering/fruiting can be affected. It's important to ventilate if you want early production out of the above veggies. It's always better to have the GH a little cooler than hotter . . . the plants will like it and so will you!

Uh, toms can take heat in the low 90s, even if they are flowering. If not, no one in OH would get fruits in summer! Lettuce (at least loose leaf types) can also survive higher temps but do tend to bolt. We got to 81 today and the GH got to 92 but I have a fan inside circulating air.

I can tell you - unfortunately from experience - they do not like 125 degrees. One day this spring, the prediction was 50 degrees and mostly overcast. It was in the low 40s when I left and I didn't open the door. When I got home, it was 60 and extremely sunny. The inside temps was 125. Fried all the baby toms (the size of a large marble or smaller) and caused some serious wilting, but the plants in dirt recovered.

YMMV,

Mike

Lettuce Bolting Resistance Project @ CU.

Dan

Thanks. This has given me some idea of maximum.
Put up my little GH 6 by 10 with flexable cover on Sunday
Put three tomatoes in it on Monday.
Wind 25 with gusts to 55 on Tuesday. My steel posts in each corner held but it tore a bunch of the tie downs loose.
Tuesday night 26 degrees... I can now say that tomatoes can not stand 26 degrees. They were just a test of how good it held temperature at night. It did not hold temp at all.
If I build another GH in Colorado, it will be steel and concrete.
Kenny

Kenny,

I made mine using 4x4 posts on the ends and middle, with 2x4 in between (16', three 4x4s, two 2x4, sunk into the ground about 18" with the holes filled with concrete. The north wall is 5/8" particle board. 2x6 boards on the top and sides as well as the bottom of the front. This thread shows pics and some of the progress during the year.

Mike

Try positioning the tomatoes within five feet of the fan. I did that last year, sometime in June, and the plant started fruiting again.