I LOVE BLACKBERRIES!!!
Comments above are correct: they self pollinate!!
Here are some suggestions for growing black berries:
I grow my black berries in raised beds. It makes it easier to tend my plants and to detect "run away" plants. My beds are 2.5 feet wide by 8 feet long. I planted 5 plants in each. Then I attached a trellis (like for a vineyard) down the length of the box to train the vines on. 2 wires at about 2 feet off the ground, 2 more at about 4 feet and 1 at about 6 feet.
You can buy "bare root" plants in early spring. Plant them as soon as you get them. If you like a particular variety and it comes in thorn and thornless choices -- PICK the THORNLESS!! Sometimes though you have to put up with the thorns to get the best tasting types!! I live in Northern California and my two faves are: "Ollalie" and "Boysen".
The first year you will get lots of vines and NO berries. The vines grow the first year, make berries the second and then die! (And need to be removed!!) If you don't have snow, you can train the vines on the trellis as they grow. If you have snow, you need to cover the vines in the winter and train on the trellis in the spring. In any case, the leaves will probably fall off in the winter and it will look like you have dead vines. HAVE FAITH!! I spray the bottom of the vine (near the ground) with white spray paint in the late winter or early spring. Because NEW vines are going to start growing (from the roots) even before my OLD vines produce berries, it helps me to tell which ones I need to cut out and remove after the berries are gone.
You must pay attention and REMOVE any "sprouts" that you see outside your "berry" area or your garden WILL be overrun with berry plants!! However, I have only minimal problems with birds "planting" seeds. And luckily (knock wood), I have not had ANY problem with birds or squirrels eating my berries!!
Good Luck and Enjoy!!!