There are two basic types of blackberry plants: trailing and erect. Trailing blackberries have flexible canes that must be tied to a trellis to keep them off the ground. Erect blackberries have stiff, upright canes that do not need to be trellised. Different varieties grow best in different parts of the country, so be sure to select an appropriate variety.
All blackberries grow best in full sun. Because blackberry plants come back year after year, it's important to prepare the soil correctly. With a garden rake, work a 2" layer of composted manure and a 2" layer of organic soil conditioner into the site to a depth of 8". If planting a trailing variety, erect a trellis.
The best time to plant bare-root blackberries in most climates is early spring. Shake off any material clinging to the roots (Image 1) and soak the roots in a bucket of water for two hours. Dig a hole the same depth and width as the roots when fanned out. Cut back the canes of the plants to 6" tall. Place the plant in the hole so that the point where the roots join the stem is level with the surrounding soil (Image 2). Backfill with soil until the hole is three-quarters full. Water well to settle the soil. Finish filling the hole and water again (Image 3).
Mulch around the base of the plants to conserve moisture and keep down weeds. Blackberries are fairly drought tolerant once established, but they produce the best berries when supplied a steady dose of moisture. Fertilize in spring and summer with a 10-10-10 fertilizer. Pollination is done mainly by honeybees, so avoid the use of pesticides.
Starting the second year, the canes of trailing blackberries will need to be trained on a trellis. Erect blackberries send up new canes from both their crowns and roots. Remove canes that pop up in unwanted places. Canes die the year after they produce fruit, so they will need to be removed.
When pruning thorny blackberries, always wear gloves, long shirt sleeves and long pants to avoid scratches.
Because blackberries are susceptible to verticillium wilt, don't plant them where potatoes, tomatoes or peppers have grown in the past three years. Also, do not plant them within 1,000' of wild blackberries as they often carry diseases that can be transmitted.
Blackberries usually mature 35 to 45 days after bloom. As they ripen, they turn from green to red to black. Berries can be harvested over a period of several weeks. Fully ripe berries should practically fall off the plants. Blackberries bruise easily, so place only a few layers of berries in a single container.