Blackberries are vigorous cane fruits whose ultimate height is highly variable, depending on both their genetic makeup and the management techniques applied by the grower. The answer to how tall a blackberry plant will grow is determined by its inherent growth habit, which dictates its natural size, and the human intervention of pruning and trellising. Environmental conditions also play a significant role in encouraging or limiting a plant’s maximum potential size.
The Three Main Growth Habits and Their Heights
Blackberries are generally categorized into three distinct growth habits that define their cane structure and natural vertical reach. Erect varieties, sometimes called bush blackberries, produce stiff, upright canes that are largely self-supporting and typically reach heights between three and six feet. This habit allows them to be grown without a trellis, though support is often used when canes are heavily loaded with fruit or allowed to reach the upper end of their height range.
Semi-erect blackberries develop canes that initially grow upright but then arch or droop, requiring support to keep them off the ground. These cultivars are more vigorous than erect types, often reaching vertical heights of five to eight feet with trellising. A trellis system is generally employed to maintain their structure and manage their tendency to arch.
Trailing blackberries have flexible, non-self-supporting canes that can grow exceptionally long, sometimes reaching ten to twenty feet in total length. Because these canes cannot support their own weight, they must be trained along a trellis. This training keeps their vertical presentation to a manageable height, typically between four and six feet for ease of harvest, regardless of the cane’s total length.
Controlling Vertical Growth Through Pruning
Maximum vertical growth is controlled by human intervention to manage space, increase fruit production, and facilitate easier harvesting. The primary method for height control in erect and semi-erect blackberries is called a heading cut or tipping. This technique involves removing the top few inches of the new canes, known as primocanes, once they reach a predetermined height, typically three to five feet.
Removing the tip of the primocane eliminates apical dominance, encouraging the cane to stop growing vertically and instead produce lateral branches. These lateral branches are where the following year’s fruit will be produced, effectively shifting the plant’s energy from height to bushiness and yield. Growers also perform annual removal of floricanes, which are the canes that have already produced fruit and will die.
Trellising systems, such as the two-wire system or T-bar trellis, are designed to keep the plant’s fruiting zone at a convenient height. Vigorous canes that naturally want to grow higher are woven or tied to wires set at five or six feet above the ground. This structural management ensures that fruit is accessible and that the canes remain supported, preventing damage from wind or heavy fruit loads.
Environmental Factors That Influence Maximum Size
The size and vigor of a blackberry plant, and thus its potential height, are heavily influenced by the conditions of its growing environment. Blackberries grow best in full sunlight, requiring a minimum of eight hours of direct sun exposure daily. Plants grown in shadier locations will have reduced vigor, resulting in thinner, shorter canes that fail to reach their maximum potential size.
Soil quality is a major factor, as deep, well-drained, fertile soil promotes the strongest cane growth. Canes will be shorter and less vigorous in heavy clay or poorly drained soils, which stresses the root system. Incorporating organic matter helps improve both drainage and water-holding capacity, creating an ideal environment for robust vertical growth.
Consistent water availability is necessary for the development of tall, healthy canes. Blackberries require about one to two inches of water per week; inconsistent irrigation leads to low primocane vigor and shorter canes. The local climate and hardiness zone also play a role, as plants stressed by extreme cold or heat will not achieve the same size as those grown within their optimal temperature range.