I have a large blackberry patch surrounded by grass. It has worked out pretty well. I started out with 2 blackberry starts 6 years ago, now my patch is in two rows, each about 12 feet long (all from the original two). I ran heavy landscape material & mulched between the rows. They found their way under the landscape material to create a 2nd row on the other side (actually this was by accident, but it worked very well).
I still have about 8 quarts of blackberries in my freezer from last year, couldn't get them all used. I usually fill two of the largest bowls I can find each time I go out, then ask the neighbor to come pick some! Just remember, blackberries produce on second year's growth when pruning. Here's a pic to give you an idea how heavy they can produce fruit (they are still red, haven't ripened yet). I have to pick on days with a calm wind because of the thorns. Definitely not a low maintenance adventure because of the thorns (but blackberry jam is the best).