Blackberries prefer cold winters and warm summers. They grow in USDA hardiness zones 4 through 10 but thrive best in zones 5 through 8. There are several methods of propagating blackberries, all fairly simple. One of the easiest is sprouting root cuttings.
Cut several pencil-thick blackberry roots that are 3 to 6 inches long. Take the cuttings in the fall, when the plant is losing its leaves and beginning to go dormant.
Place the root cuttings in a plastic baggie along with some damp peat moss. Seal the baggie and place it in the vegetable crisper of your refrigerator and leave it there until the following spring.
Remove the baggie from your refrigerator once all possibility of frost is gone from your area. Allow the cuttings to thaw on a damp paper towel overnight.
Choose a sunny, well-drained location. Loosen the soil in your garden and mix potting soil with your garden soil until the mixture is approximately 50/50. Make 1-inch-deep trenches in the soil and lay the blackberry roots horizontally in each trench and gently cover with soil. Plant roots 3 feet apart with rows at least 18 inches apart.
Water the soil gently but thoroughly. Keep the soil damp but not soggy. Your blackberries should begin to sprout within 14 to 21 days.