I have a lot of wild blackberry bushes growing in my yard under trees, so they are mostly in the shade. I moved here a year ago and had hoped that they would produce, but I haven't seen but one blackberry. Do they need sun? I am pruning them to the ground at this moment, and so I know they will come back, but is there something I can do to make them produce, or do they just need sun? I also wanted them for birds, but I have yet to see any bird nests in them, so I am not sure if they serve a purpose.