I have grown this type of Arundo for over 5 years now and it always impresses me with its speed, height, and beautiful foliage. I have mine in a large pot as to prevent it from spreading and always cut mine down after the frosts have finished. Whilst the long stalks will happily reshoot, despite looking a bit tatty through the winter months, I much prefer the cleaner new growth that emerges as if left side shoots will spring out along the nodes of last years growth. If in the ground and occupying a large area this can be attractive and make the presence of the plant feel much larger, however new growth will be much cleaner and shoot straight up very unlikely to produce side shoots that year.