No, you were correct Sandy, my friend was hibernating the tortoises directly into the substrate of a greenhouse.

Lol its getting late:0) Thats my excuse anyway.

I think this would be different with outside ground temps particularly with the cold winters we get in parts of the U.K. Besides torts don't necessarily always bury themselves to ideal depths during hibernation. I know my hermann's doesn't. But then again she originates from the wild were the soil is sandier, requiring less digging, and likelier to cover her more completely unlike the hard outdoor soils we get here in parts of the U.K. Indeed, I am considering using top soil in my torts hibernation box this year as I had previously been using garden clay which I don't think is very good for digging down in to. Also, as my tortoise originates from a milder climate , I never have or would risk hibernating her outside in the colder winters we get here in Ireland. I think U.K captive bred tortoise because they are born and reared here are more tolerant of the varied U.K regional climates. So my wild tortoise is definitely at a disadvantage when compared to these, though she has acclimatised quite well to Irish weather over the past 30 years. I am ,however, still cautious with her. With regard to greenhouses these are self contained, protected environments and act like artificial eco systems so temperature readings there are not like the true ground temperature readings one would get outside which are more effected by seasonal conditions.The advantage of greenhouses is that temperatures are milder and much more stable there, added to this is the fact that they protect your tort from the outside elements so all in all they make great hibernation places.
Kind Regards
Freddy

Thanks for sharing all of you.