I am collecting leaf litter to add to the substrate for my soon-to-be Hermann's. All of the material I've gathered so far is from my own yard and free of chemicals: dried palm fronds cut to 1-2 inches and fallen rose petals and leaves from my climbing roses. My neighbors have a HUGE sycamore tree that sheds massive numbers of great, dry leaves. I know they don't spray (I've talked to them about it) so the only question remaining is whether there's any problem with sycamore leaves. I've got TONS of dried oak leaves in my yard, but I understand they're considered toxic to torts, so I'm not using them. I haven't been able to find anything about sycamore in a general online search or the Tortoise Library.
