I thought this might make an interesting subject for discussion. As I am sure some of you will know, part of the novel "Lorna Doone" is set during the winter 1683-84 (coldest in the CET record), and features some very evocative passages of the winter on Exmoor, including trees exploding, because of the intense cold. Of course, it is a novel, so the exploding trees on Exmoor may be artistic licence, but it seems to be historical fact, at least somewhere in Britain during that winter, think that John Evelyn recorded it in his diary, and also this from John Claudius London:  

"The history of frosts furnishes very extraordinary facts. The trees are often scorched and burnt up, as with the most excessive heat, in consequence of the separation of water from the air, which is therefore very drying. In the great frost in 1683, the trunks of oak, ash, walnut, and other trees, were miserably split and cleft, so that they might be seen through, and the cracks often attended with dreadful noises like the explosion of fire-arms. In the frost of 1837–8 large bushes of heath had their stems split by the frost into shreds, and the wood of the evergreen oak and that of the sweet bay was cracked and split in a similar manner."

So I was wondering if anyone knows, or can approximate what temperatures were reached during that winter, because I've done some research and can't find much info on the temperature required to make British tree (e.g. English Oak), explode. Maybe minus 30? 

Also was wondering if there are any reports of trees exploding in the greatest freezes of the 20th century, e.g. Jan 1940, 1963, maybe Jan 1987.

There doesn't seem to be much direct evidence that I can find having done a rather lengthy google search but what I can surmise is that

A) It is a real phenomenon

B) It depends on the type of tree - some can withstand much lower temperatures than others (I think probably below -20c for our Oak trees)

C) The range of temperature and weather type plays a big part in so much as If the day has been relatively warm and sunny then the sap in the tree will have been encouraged to start rising - especially if it is spring. This sap is then frozen during the very low temperatures of the night.

Here is a link to exploding Olive trees - here the temperature was 21c in the day and -17c at night.

http://www.mirabeauwine.com/the-devastating-frost-of-1956/

The next winter close on in severity was the winter of 1740. Temperatures were down to -22C in Essex and the Home Counties in that winter.

January 1684 had a CET of -3C - so temperatures must have been down to -20C and below at some point then.

January 1740 had a CET of -2.8C and there is anecodotal evidence of a weekend in that month in which the CET was -9C for 48 hours.

Thanks for the replies. Personally I think it's a fairly safe bet that minus 30 was reached during the LIA, at a present-day weather station location. I suppose Jan 1987 is what some of coldest spells would have been like.