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.