You need to remove the burlap from the root ball of trees. Suppliers traditionally used standard burlap because it's tough, its natural fibers rot in the hole, it doesn't disturb the soil around the roots, and it makes planting easier. But today's burlap may be made from synthetic fibers, which are difficult to distinguish from traditional burlap and don't decay in the soil. Cut away as much burlap as possible from the sides of the root ball after you've positioned it in the hole. Because most roots grow outward rather than downward, this will allow them to grow without restraint. If the ball is encased in a wire cage, cut away the cage too. Then you can get at the burlap and remove it.