I just read a piece on ground respiration yesterday. I never had thought about it. You are describing part of that process I believe. Temps, Pressure, Moisture all contribute. Might have been archived in some of the Rutgers stuff pt03 (Lloyd) had referenced to on another topic.

__I just rototilled my garden spot. Its 38 degrees now .. last night 16 and tonight 13 predicted. Nothing growing, just trying to get that very last Bermuda grass (wire grass here) root to the top so it can kiss its fanny goodbye.

In the classroom we called it "frost heave". Some interesting pictures on Wikipedia. Google sites discuss more to do with structural problems although there are a few gardening ghits.

It does a lot of aeration and mixing, especially when you rake it flat in the spring.

We always wanted the ground to freeze 6-8" deep during winter. Plants seemed to do better the following summer - the soil would drain better in wet conditions and hold moisture better when the annual drought hit.

Mike

The lack of frost heave here in the deep South is why we have serious problems with rootknot nematodes and our gardening friends to the North do not. The freezing of the soil kills them.

I knew there was a good reason to live in a frozen wonderland(:

I've read that bulbs don't like the cycle and it is prudent after the first freeze to heavily mulch bulb beds to stop the cycle. I'm doing that this year.

I think you're right. I can remember my mother talking about her bulbs being "heaved" out of the ground from the constant freeze cycles of the NE Ohio Winters.