Lots of us add leaves to our litter. Some folks use them as the main component of their deep litter. I didn't because I got my chickens in late winter (February) so there weren't any leaves in my yard - just snow. But I've been adding them now and the girls love scratching around in them! They break down and blend into the litter fairly quickly. This year we are stacking and storing the leaves instead of the usual burning them off so I can add them from time to time all winter.