In1988 I planted a walnut tree, its grown well and produced plenty of nuts, now 40ft high and was 40ft wide until I pruned it. All the leaves and smaller branches have been shredded,. This load I have stored in a large builders sand bag, approx. 1 cubic metre. I have not added this directly to the compost heap, because something in the back of my mind, suggest they may be toxic. Can you please advise on this problem, and are there any other leaves and shreddings that would be best left off the compost heap? My wife is a keen flower arranger, so we have allsorts of pruning and leaves to dispose of, ideally with all my vegetable waste on the compost heap.