Blackberries are perennials that produce both growing canes and fruit canes in a two year cycle. The cane that grows this year will produce fruit next year and then die. According to Oregon State University, there are two basic growing types for blackberries: trailing and erect. Trailing blackberries also known as dewberries, require the support of wire or fencing to keep the fruit off the ground. Established blackberry plants will remain productive for many years.
Select the site. Choose an area that receives full sun and is removed from any native areas growing wild berries to minimize cross breeding. In cooler areas, select a site with some slope that will allow the colder air to move below the plants. The site should be well-drained.
Prepare the site. Clear the area of any debris and till down several inches to get the soil workable. Adding organic matter will improve aeration and free nutrients for the plants. Soil that has issues with structure (too much clay or sand), pH (too high---pH of 6 is ideal), or fertility (not enough) should be amended with organic matter and nitrogen. Thoroughly work the soil before planting.
Choose cultivar. Blackberries can be grown throughout most of the United States if care is given to the plant selections---and you will have many choices. As a general rule, trailing blackberries are less cold tolerant than erect blackberries. Clemson University suggests varieties for southern growing such as Choctaw, Cheyenne, and Arapaho. Midwestern blackberry varieties include: Thornless Boysen, Youngberry, Thornless Hull, Lockness, and Triple Crown that are winter hardy to zone 5. Zone 4 and above is somewhat challenging for blackberries, but gardeners have been successful with some cold tolerant plants.
Plant blackberries in early spring in the North; in late winter or early spring in the South. Blackberries have shallow roots, so dig your hole just deep enough to cover the contained roots. Place the plants 3-6 feet apart. Fertilize and mulch as soon as the cane begin to bud out. Add fences or trellises for training the trailing variety of blackberry.
Care for blackberry plants. It will take 2 years for you to be able to harvest blackberries since the fruit is set on year-old canes. Fertilize each spring and remove dead canes in the fall. Continue to mulch plants and add about an inch of water per week while the plants are active. Harvest berries when they remove easily from the plant. The plants are susceptible to viruses, fungi, and some insect pests. Treat as recommended by your agriculture agent or master gardener.