Blackberry Care & Harvesting by National Gardening Association Editors
Each year blackberry plants produce new canes from the crown just below the soil surface, and from roots that extend some distance out. Each cane lives for 2 years. The first year a cane produces only leaves, the second year it bears fruit. It won't fruit again, so old canes should be pruned out as soon as possible after the harvest to prevent disease from attacking the plant. Pruning reduces stress on the plants. Keep enough fruiting canes to have a good crop and remove the rest along with undesired root suckers each year. There are two different types of blackberries, upright and trailing, and each requires a different pruning method. The upright ones produce arching canes that can just support themselves. Included in this group are the semi-uprights, which flop a bit but can be treated just like the uprights. The trailing types sprawl and must be supported on wires.
The two groups also bear their fruit differently: upright kinds have fruit at the tips of the canes, trailing kinds have berries all along their length. The trailing types tend to be less hardy than the uprights, but they are usually more productive. Your choice depends on where you live, how much space you have, and the variety of fruit you prefer.
If you want to support upright-growing blackberry plants, you can train them to grow neatly around posts. Space plants 3 feet apart in rows. Each plant should be attached to a 6-foot post about the thickness of a wrist or to a 2- by 2-inch board sunk about 1 foot into the ground. When the new canes (the leafy ones) are about hip high, pinch back the growing tip of each one; this encourages the canes to branch out during the rest of the season. The next summer the leafy canes become fruiting canes, bearing amazing clusters of fruits at a height where they're easy to pick. Later in the summer, immediately after you've harvested the blackberries, cut off the fruiting canes close to the ground.
Wire Trellis System
Give trailing plants a wire trellis or fence to grow on instead of a post, and spread the canes out as much as possible. How much the canes will grow in 1 year varies; one way to handle the very long ones is to wrap them around two strands of wire. The fruit dangles within easy reach, minimizing scratches while harvesting.
In northern areas, where winter protection is necessary, set the canes on the ground for the winter, cover them with clean straw or leaves if you don't get much snow, then carefully place them up on the wire in early spring before they start growing again. In milder climates, train the new canes on the wire as soon as you've cut out the fruiting canes and leave them right there through the winter. Each year remove the canes that have fruited and allow several leafy canes to replace them. In areas with long growing seasons, the vines may get extremely long and require a dormant-season pruning. Cut them back to about 8 to 10 feet in late winter. Fruiting is heaviest near the base of the canes, so you won't be losing much of the crop and the resulting berries will be larger.
Berries will ripen over a period of several weeks and should be harvested every 2 to 4 days. Pick berries in the cool of early morning and avoid bruising them. Refrigerate the berries immediately; they'll keep for 4 to 5 days at 35° F if picked when warm, berries don't keep as long.