In order to understand how to prune blackberries it’s important to understand the basics of how blackberries grow. Blackberries are perennials.This means that the root system will live for many years. The root system produces new canes yearly. Canes produced are biennial and die after two years. The first year of growth on a blackberry is called a primocane. For many varieties of blackberries (though not all) this is primarily a vegetative year of growth and will not produce fruit.