Where does the moss in my gutter come from and why is it always spread all over my patio? The moss in your gutter is thriving on nutrients provided by decomposing debris. It can get there by falling from your roof or by natural germination from spores and will only grow in places where the light levels are just right. Birds looking for grubs and insects are responsible for turfing it out onto your patio. Gutter clearing every 2 to 3 years (yearly for properties surrounded by trees) will prevent this.