Outcome

When the freezing cold is prolonged, it can penetrate. Actually, it is the heat that escapes. With a short lived frost or freezing you can easily protect your plants but when it get that cold, even 3kw heat in a bog greenhouse might not help.

I hope they will come back.

That freezing cold is a killer. Im in Northern CA where we usually don't get too cold here. However, we had a week of 20's (yes, that is cold here) and everything in the greenhouse survived- without a heater. My Manzano did not make it though. It was outside and too big to put in the GH. It was even covered, Lasted 2 seasons too. I pampered those from seeds. So sad to see them go.
So, Mother Nature finally took her children, but I was surprised to see 4 sibling growing in the soil. Some seeds must have fallen and resprouted.
Mother Nature also gives back.

As to "too much heat" in a GH, I have not had that experience to make a comment on. Re-reading the post, I see I did miss the true intention. Sorry for the misunderstanding.

This post was edited by RonnyB123 on Sun, Jan 12, 14 at 20:55

I think the OP was saying that it was actually heat that fried his plants. The combo of the sun and the heater.
I understand this, as I have one of those small 5 foot high by two feet wide by 1.5 feet deep greenhouses. Even when the temps are below freezing, it can get well above 80 or 90 in there when the day time sun is beating down on it and it isn't vented.