The Royal Empress Tree (Paulownia tomentosa) is known for its astonishing growth rate, sometimes gaining 15 to 20 feet in height in a single growing season. This rapid vertical development is supported by an equally aggressive subterranean architecture. This vigorous root system has earned the tree a reputation as a problematic invasive species in many regions. Understanding the nature of these roots is important, as they are the source of the tree’s structural threat and its persistent, regenerative capability. The root structure is designed for survival and rapid colonization, making the tree a challenge to manage near human infrastructure or natural ecosystems.
Root System Structure and Depth
The Paulownia tomentosa root system combines deep-reaching development with far-extending lateral spread, creating a robust anchor for its rapid growth. In certain soil conditions, the tree develops a deep taproot, which contributes to its drought resistance and ability to thrive in poor soils. The problematic elements are the coarse, fleshy lateral roots and the dense network of shallow feeder roots.
These lateral roots are widely distributed and can extend horizontally, sometimes reaching a spread of three times the width of the tree’s crown. A mature tree can impact an area with a root diameter of 28 meters or more, posing a concern for nearby foundations and pipes. The majority of the fine, nutrient-absorbing roots concentrate within a relatively shallow radius, typically 40 to 100 centimeters of the soil surface. This extensive root mat aggressively monopolizes soil resources, crowding out surrounding vegetation.
Mechanism of Aggressive Spreading
The aggression of the Royal Empress Tree root system lies in its powerful biological mechanism for vegetative reproduction. The roots possess a high concentration of adventitious buds, which are dormant growth points capable of sprouting new, genetically identical trees, known as root suckers. This ability allows the tree to regenerate rapidly, particularly following injury or removal of the main trunk.
When the main tree is cut down—a common technique called coppicing—the massive, intact root system is left with a huge reserve of stored energy and no canopy to support. This prompts an immediate response where dozens of root suckers erupt from the lateral roots, often many feet away from the original stump. These suckers can grow rapidly, sometimes exceeding 15 feet in height in a single season as they draw on the established energy reserves. Furthermore, the tree can regenerate from small fragments of root left behind during attempted excavation. If the root system is disturbed, each resulting fragment can activate its adventitious buds, initiating the growth of a new, independent tree. This regenerative capacity is the core challenge that makes the tree difficult to eradicate.
Mitigating Root System Damage
Effective management of the Royal Empress Tree requires an approach that targets its regenerative root structure, rather than simply removing the canopy. For complete eradication, the most effective method is the “cut and treat” technique. This involves cutting the trunk as close to the ground as possible and immediately applying a systemic herbicide, such as concentrated glyphosate or triclopyr, directly to the freshly cut stump surface within minutes. The herbicide is drawn down into the root system, killing the entire structure by exploiting the tree’s vascular system.
For those avoiding chemical treatments, the alternative is a long-term strategy of exhaustion. This requires continually cutting or mowing down every root sucker that appears, often for several years, to prevent the roots from photosynthesizing and replenishing stored energy. This denial of foliage will eventually starve the extensive root system, though the process is lengthy and labor-intensive. To prevent infrastructure damage, new plantings should be sited at a significant distance from foundations, retaining walls, and utility pipes, often requiring a setback of at least 50 feet to account for the lateral root spread of a mature specimen.