I use any leaf litter that is not from overtly toxic plants (ie: oleander, Castor bean pods, mistletoe etc...). I have used rose flower and leaf little as well as oak, mulberry, and Camellia leaf litter. I don't clean it if I'm fully certain that no pesticide or herbicide has been used there or nearby. I prefer to keep the natural flora and fauna (bacterial, fungal, and entomological) intact to do as it will in my vivariums. I especially like the action of arthropods like "pill bugs/wood lice and spring tales. Also, as anything as they are in the rest of my house, I have had ants set up colonies in my gecko vivs, and I can clearly see them cleaning up dead/uneaten feeder insects.

Go, and be dirty.

Jared
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With great power, comes great responsibility.
-Ben Parker