I have a 3 or 4 year old blackberry bush that I've never pruned. Every year new growth & lots of blackberries come back on the old 'branches', EXCEPT this year. We had a rough winter and it's like my bush decided to just start over and I have new growth coming up from the ground and a bunch of bare branches above it. Should I cut those old branches back? And if the answer is yes, can I do it now or should I wait 'til the end of the season?