When you say wild blackberry i’m not certain what species you have.  

You shouldn’t have to do anything to them. Disturbing the soil can introduce weed competition that they don’t like. They grow along the edges of woods and are not picky about the soil. While you would fertilize cultivated blackberries, fertilizing wild blackberries may interfere with their normal growth cycle. They don’t like a lot of sun. They don’t have the same growth habits and crop potential that domesticated blackberries have. 

Blackberries are biennial and have primocanes and floricanes. The primocanes are first year growth. The floricanes are second year growth and are the canes that flower and produce fruit. 

http://www.minnesotaseasons.com/Plants/Allegheny_blackberry.html

https://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=PDROS1K710