Most people have a love hate relationship with blackberries. They love the berries and hate the vines.
"One of my jobs as a youth was to try to keep the blackberry vines from invading the orchard," recalls Jerry Goodspeed, Utah State University Extension horticulturist. "I would get the machete, dress in war fatigues, and kiss my family goodbye. If I came back having lost no more then a quart of blood, I considered myself victorious."
Blackberries are related to raspberries and have similar growth habits, Goodspeed says. The difference is evident at the time of harvest. Raspberries separate from the receptacle (the part of the flower that holds the berry) while blackberries do not.
Blackberries require plenty of moisture, he says. While they are growing and ripening it is essential they receive adequate water. If you forget to water them for about 10 days during their crucial ripening period you may find that most of the berries end up small, hard, and not properly mature. That said, they are not picky about where they are planted. So long as it is not in standing water or in an area with a real high water table.
"Blackberries do their best with plenty of space to grow. It is best to work some organic material into the soil before planting. Leave at least 4 feet between each plant, or even 6 to 8 where possible. Most blackberries produce better when trained to a trellis, along a fence, or on a wall. If left to sprawl on their own, they tend to spread out, quickly invading the neighbors garden or hot tub. One problem with some blackberries is they do not have enough sense to die once they have borne fruit. They send out new growth from the terminal end of the old canes and just keep growing. This gives them their trailing and invading abilities."
Like raspberries, the roots of blackberries are perennial, while the tops are technically biennial. Goodspeed says this means the roots live for many years, but the canes grow vegetatively for a year, bear fruit the next year, and then die. Every year the plant sends up new canes to replace those that died.
Though thorny, pruning most blackberries is easy, he says. Simply remove those canes that bear each year and let new ones take their place. Every year some canes will bear fruit, while others grow vegetatively to produce next year's crop. If a cane decides to continue to grow instead of die, cut it back to a lateral, or remove it completely to keep it in check.
Most blackberries respond well to early spring fertilization with an all-purpose fertilizer such as a 10-10-10, or a 16-16-8. After they are through producing, add a small amount of nitrogen fertilizer to stimulate growth, Goodspeed says.
"Many varieties of blackberries grow in our area. The thornless are the most popular but generally the least hardy. I grow two thornless at home, 'Arapaho' and ' Navaho'. Both seem to do quite well and have a good flavor. Two other thornless varieties include 'Dirksen Thornless' and 'Black Satin'."
Dennis Hinkamp - Utah State University Extension