Yea, Annie, my maternal Grandmother would take me blackberry picking just across the street; we lived on Long Island, New York.
Three years later these blackberries "trees," which grew in the woods and stretched for the sun, were incredibly high and the berries were so big! Then the bulldozers came for new houses and they were gone forever.
Some kids were the designated climbers and would harvest them. In fact, one guy loved the heights so much that he became a pole vaulter and eventually became a state champion.
Back then and before the 1950s, Long Island helped feed New York city and itself, so there were a lot of farms [my great grandparents owned a small farm], the soil seemed to be perfect, and manure was in abundance. It seemed like everything grew well and the immigrant population segments seemed to have a lot of growing "secrets."
Last year I sent away for ten blackberry bushes for what I thought was a bargain. One survived and that happened to be in a group that I shared with a friend. This year I will go to a local nursery and pay the yuppie prices and get three good plants: