Flower in the Hedge

I was walking upstairs and I stopped on the landing to look out the window, which I do often.  Something caught my eye, and I looked closer and saw that it was a single flower bloom way up at the top of the hedge that separates our yard from the people next door.  It hasn't been cut for a couple of years, so it is about nine feet tall!  Where did this bloom come from?  Well, there are all kinds of vines that grow up inside the hedge.  We start each Spring by going into the hedge and cutting the vines and pulling them out.  I am glad we missed this one!  The photograph below shows where the flower is, and how small it is compared to the hedge.  Amazing that I spotted it!