How long??????????

I've an enormous pile of old turf covered in thick black plastic in my back garden. How long will it take to rot down, and can I use it in my garden as top soil in my borders? Thanx, Dougy.

 

'They' say 6 months but it depends a lot on what type of soil you have and where the heap is, sunny/damp etc. If it's clay in a damp shady spot it could be more likr 18 months.