Hello tanith, I bought a blackberry bush from Aldi in Brittany three years ago and last year I had 22lbs of fruit.
I was amazed and eventually had to freeze much of the blackberries. I spread them on a tray, threw any away that were other than perfect then gave them a quick brush with a dry paintbrush. I didn't 'open' freeze them, just bagged them in zip lock bags in 1lb quantities.
I have been defrosting them for pies and jam making. They defrost very well and are not too mushy which is just as well because this year's crop is looking dodgy after a few months of unusual weather patterns in Brittany. Hope this helps.