like i said before i have never heard or tried this method but i am intrigued. so what exactly does it do, does it raise the temp significantly or does it just keep frost at bay. last year i overwintered some very young perennials in the unheated glass greenhouse and although they did fine there was definite evidence of frost, as standing water in there iced over as much as 1/4 inch thick quite a few times during the coldest months. so would less robust plants such as aubergines over winter OK with this method or should i stick to original plan of keeping them in the conservatory over the winter???