I think you should have called a gardener!
There are not many jokes in the gutter cleaning industry but this is one we use often when faced with a lovely lawn of grass growing in the gutter, like in this photo taken todat at a job in Headley. Where does it come from?? Birds and pigeons are most likely to blame for grass growing in your gutters.
The moss and silt fall off your roof creating a nice soil and then along come the birds and do there business while enjoying the view or having a bath in your gutters. Add a bit of rain which the gutters are very good at catching and voila, a beautiful bit of grass that the gardeners at wimbledon would be proud of....