Thatch is caused by fast release fertilisers or over fertilising making
grass roots stay near the surface. Leaves do not cause thatch and are
beneficial for a natural fertiliser and in studies reduce fungal
problems. The only time I had thatch was with Chemlawn liqued type
fertilisers. Mulching 6 inches of leaves every fall till pieces are
small has hurt nothing and reduced my fertiliser need to nearly nothing.