My neighbour has built a huge monstrosity of a building attached to his garage at the bottom of garden. I have only a four foot gap between my fence and greenhouse to plant in. I need to grow quickly and to be evergreen and tall, to get to around 15 ft min. I have thought of pyracantha on trellis. It needs to be low maintenance due to space restrictions. Any ideas please. I have grown a conifer in the corner but growing very slowly at the moment. HELP!