Not an expert by any means but I was digging along my Rasberries last week and the roots extended quite some distance , near a meter each side . When planting them I was advised to dig a trench about a foot deep and wide ( see I work on both measurments) and put a good layer of composted manure in the bottom before back filling with soil . the other advise I was given was to throw any mushable materials at the base of the plants, ie, green leaves from other veg , corn stalks, garlic shoots what ever you have to keep moisture in the roots and supress any thing growing under them.Also it takes 2 years before you get any fruit from them, this is year 2 for me and I have got a few kilos but not as much as the guys who donated the plants to me, surely you could use the plants you already have .