Remove all debris from the planting area.
Use a tiller to turn several inches of organic compost into the soil.
Rake the area level.
Trim off broken or dead limbs and foliage. Loosen the plant roots by gently pulling them down and out from the plant.
Dig a hole twice as deep and wide as the blackberry plant's root ball. Fill this hole with additional compost.
Center the plant in the hole.
Pack the compost and remaining soil around the root ball.
Water the plants thoroughly to finish settling the earth around them.
Add 3 or 4 inches of mulch around the plants. This retains moisture and keeps weeds under control.