Blackberries (Rubus) produce sought-after summer fruits, but their vigorous growth often concerns gardeners. Blackberries spread rapidly, a trait that ensures their survival in the wild but makes managing them challenging in cultivated spaces. Understanding how these plants colonize new territory is key to successful cultivation and control. They utilize dual methods—one underground and one above ground—to establish new, independent plants and create dense thickets.
The Dual Mechanisms of Blackberry Spread
Blackberries employ two distinct strategies for vegetative propagation, allowing them to rapidly increase their footprint. The first mechanism involves underground expansion through the formation of root suckers. The perennial root system sends out lateral shoots that travel horizontally beneath the soil surface.
These lateral roots then generate new canes, known as suckers, which emerge vertically from the ground, often several feet away from the original plant crown. Prompt removal of these suckers is necessary, as each one is capable of developing into a new, fully independent blackberry plant if left undisturbed. This root-based spread contributes to the dense, interconnected nature of a blackberry patch.
The second method of spread occurs above ground and is called tip rooting or tip layering. As the plant’s long, arching canes (primocanes) grow, their tips naturally bend toward the ground. When the cane tip contacts the soil, it forms adventitious roots, effectively anchoring itself.
Once the tip has rooted successfully, the cane connecting it to the parent plant can be severed, resulting in a genetically identical, separate new plant. This process is particularly effective for varieties with long, flexible canes, enabling them to quickly colonize a wide surrounding area.
How Growth Habit Influences Spreading Aggressiveness
The aggressiveness of a blackberry plant’s spread is directly tied to its specific growth habit, which determines which of the two propagation methods is dominant. Erect blackberries, which have stiff, upright canes that are largely self-supporting, primarily rely on the production of root suckers. These varieties tend to form a dense hedge-row pattern because new canes emerge close to the original plant crown.
Conversely, trailing and semi-erect types possess long, flexible canes that are not self-supporting and often require a trellis. This structural difference makes them highly dependent on tip rooting for expansion. Their canes easily arch, touch the ground, and establish new plants far from the parent, leading to faster, wider colonization.
Wild varieties, such as the invasive Himalayan blackberry, are typically the most aggressive, combining vigorous root suckering with prolific tip layering. Modern cultivated varieties, especially certain thornless selections, have often been bred to exhibit reduced suckering and less vigorous cane growth. This genetic modification makes them generally easier to contain than their wild counterparts, although they still require management.
Strategies for Controlling Blackberry Expansion
Controlling blackberry expansion requires a dual approach addressing both underground and above-ground spreading mechanisms. To prevent subterranean spread, physical root barriers are highly effective. These barriers, made of heavy-duty plastic or metal sheeting, should be installed to a minimum depth of 18 to 24 inches to intercept the majority of lateral roots. Leave about two inches extending above the soil line to prevent roots from growing over the top edge.
For above-ground containment, aggressive pruning is the most practical technique to manage tip rooting. This involves regularly “tipping” the primocanes—cutting off the growing tip—once they reach a manageable height, which removes the tissue capable of rooting. Training the canes onto a trellis system is also a preventative measure, as it keeps the cane tips elevated and away from the soil surface.
To manage existing underground spread, remove suckers as soon as they appear. Simply clipping them at the soil line is insufficient. Effective removal requires digging down to sever the sucker from the main root system, preventing immediate regrowth from the remaining root fragment.