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Erect blackberries have stiff canes that are upright and arching. They can be trellised or grown in the landscape as a hedge or shrub border. Trailing blackberries have flexible canes that must be tied to a trellis so they don't flop to the ground.
All blackberries grow best in full sun, and almost all varieties are self-fruitful, meaning that you need to plant only one cultivar. As a rule of thumb, five or six plants will produce enough berries for a family of four. Each blossom will produce a sweet, juicy blackberry.
Horticulturalists have been hybridizing blackberries for nearly a century and have developed a huge number of blackberries varieties. Different varieties grow best in different sections of the country, and it's important to select a variety that's well suited for your climate.
Blackberry trellises are simple to build and require only a few dollars' worth of materials. To build a simple trellis, sink two 8' pressure- treated 4x4 posts 3' deep in the ground (Image 1). If you're working in sandy soil, you can add a quick-setting mortar mix to anchor the posts. In clay soil, simply tamp down the soil to hold the posts in place.
The posts can be set anywhere from 10' to 20' apart. Make two marks on each post, one mark at 2-1/2' off the ground and the other mark at 4-1/2' off the ground. Then, at those marks, attach 9-gauge coated wire to the posts with staples (Image 2).
During the first growing season, blackberries don't need to be trained to a trellis. Starting the second year, the canes should be tied to the trellis. One method involves loosely tying primocanes to the wire as they develop. The best time to start is before the buds swell in early spring. When the canes are tall enough to reach the top wire, tie them horizontally along the wire. Another method some gardeners use it to train only the floricanes to the trellis and let the primocanes sprawl on the ground.
Since blackberries are perennial plants that come back year after year, it's worth your time to get the soil prepared correctly.
Blackberries grow best in fertile, well-drained soil. Unless your soil is already perfect, you'll want to add a 2" layer of composted cow manure (Image 1) and a 2" layer of an organic soil conditioner (Image 2) on top of the soil and work them in to a depth of 8"-10".
Blackberries do best if the soil pH is slightly acidic, somewhere between 5.5 and 7.0. Take a soil pH test (Image 3) and, if necessary, add lime to raise the pH or sulfur to lower the pH.
It's best to plant blackberry shrubs in the early spring or, in warmer climates, in late fall. Blackberries can be purchased either bare-rooted or containerized. If your new plants are bare-rooted, shake the packing material off the roots and set the plants in a bucket of water for several hours. This keeps the roots from drying out, which you want to avoid at all costs.
In most cases, the canes of a blackberry shrub will have been cut back at the nursery before you purchase them. If your new blackberry shrubs have not been cut back already, cut the canes to 6"-8" inches. By pruning back the canes in the first season, you will not have a crop the first year, but you will allow the plants to put their energy into developing a strong root system. The plants will be healthier and more productive in the long run.
To plant, dig a planting hole wide enough to accommodate the roots without crowding them (Image 1). Place the blackberry shrub in the hole, positioning it so that the crown of the shrub, where the stem and the roots join, is level with the surrounding soil.
When you've filled the hole about three-quarters of the way with soil, stop and pour about a gallon or two of water into the hole (Image 2), which will help settle the soil and get rid of any air pockets. Finish backfilling, lightly tamp down the soil with your hands and water well once again.
Different blackberry varieties have different spacing requirements, and you should follow the recommendations on the plant label or the recommendation of your extension service.
The best way to determine proper fertilizer rates is by way of a soil sample test (Image 1). If soil sample results aren't available, fertilize two times a year (spring and summer) with a balanced (10-10-10 type) fertilizer with micronutrients (Image 2). You can also look at the blackberry foliage. Leaves should be a dark green. Pale-green or yellowing leaves typically indicate a nitrogen deficiency.
Blackberries are fairly drought tolerant once they are established, but they produce the best berries when they have a steady supply of moisture. Sufficient water is especially important right before harvest. Typically, blackberries should be watered once or twice a week during summer droughts.
A drip irrigation system works well with blackberries (Image 3). It puts the water right at the roots of the plants, where the water is needed. It also keeps the blackberry foliage dry. This reduces the chances of disease, since wet foliage encourages disease formation and spread.