Paulownia tomentosa, commonly known as the Empress Tree or Princess Tree, is a deciduous hardwood native to China prized for its ornamental qualities and rapid growth rate. It can achieve vertical growth of up to 20 feet in a single year, making it one of the fastest-growing species cultivated in temperate zones. In spring, it produces showy clusters of pale violet, foxglove-like flowers that release a pleasant vanilla scent before the foliage emerges. The species is characterized by massive, heart-shaped, velvety leaves that can reach up to 16 inches across. However, this vigorous growth habit and prolific seed production contribute to its classification as an aggressive and invasive species in many regions, necessitating careful management in a residential setting.
Establishing the Tree
Selecting the ideal location for planting the Empress Tree is the first step in successful cultivation. The tree requires a minimum of six hours of direct sunlight daily to ensure optimal growth and abundant flowering. While the species is highly adaptable and can tolerate poorer soils, it develops best in well-drained, sandy loam with a slightly acidic to neutral pH (5.5 to 7.5).
Planting should occur in early spring or autumn when the soil is easily workable. The planting hole should be dug to be at least twice the width of the root ball. Ensure the root collar sits level with the surrounding soil to prevent issues like collar rot. The tree is generally hardy down to USDA Zone 5, but its flower buds, which form the previous summer, are susceptible to damage when temperatures drop below 0°F.
Due to the Empress Tree’s potential for aggressive root spread and eventual size, careful placement away from structures and utility lines is advised. Its fast-growing, shallow root system can extend outwards significantly. Furthermore, its brittle wood makes it prone to wind damage, so choosing a site protected from strong winds can help mitigate the risk of limb breakage.
Watering and Fertilization Requirements
Newly planted Empress Trees require regular, deep watering during their first growing season to establish a robust root system. Consistent moisture is necessary, usually delivered by watering deeply once a week, allowing the top layer of soil to dry slightly between applications. Once established, the tree is drought-tolerant and requires little supplemental water except during prolonged periods of heat or dryness.
The species can grow even in nutrient-poor conditions, but its rapid growth benefits from a balanced nutrient supply. If the soil is not naturally rich, apply a slow-release, balanced fertilizer (such as an NPK ratio of 10-10-10) in early spring as new growth begins. Avoid over-fertilization, particularly with high-nitrogen formulas, as this promotes excessive foliage growth at the expense of flower production and can reduce winter hardiness. Also, avoid using chlorine-containing potassium fertilizers, as the element can negatively influence the tree’s health.
Managing Growth and Size
Controlling the Empress Tree’s aggressive size and tendency to spread is a primary concern for residential growers, requiring specific pruning and management techniques. For the largest possible leaves, a technique called coppicing involves cutting the main trunk back to the ground in late winter or early spring. This radical pruning encourages new, vigorous shoots that bear leaves up to three feet long. However, this method sacrifices the spring flowers since blooms form on second-year wood.
For maintaining a traditional tree shape, light pruning should be performed in late winter to remove dead, damaged, or crossing branches, which improves air circulation. Alternatively, the tree can be pollarded, which involves annually pruning the branches back to the main trunk to maintain a consistent crown size. Pruning manages the canopy and is a crucial step in controlling the tree’s spread.
Managing the reproductive spread involves two major challenges: aggressive root suckers and copious seed production. Root suckers can emerge many feet away from the main trunk and require immediate mechanical removal or chemical treatment, as they can grow over 15 feet in a single season. Cutting root suckers without chemical application usually results in immediate and vigorous re-sprouting from the extensive, shallow root system.
To prevent seed dispersal, the oval, woody seed capsules must be collected and disposed of before they ripen and open in the fall. For managing established suckers, a localized cut-stump application of a concentrated herbicide (such as a 25-50% solution of glyphosate or triclopyr) is necessary to kill the root fragments. Continually cutting back the re-sprouts can eventually starve the root system, but this non-chemical approach requires persistent effort over multiple seasons.
Dealing with Common Issues
The Empress Tree is generally hardy, but it can be susceptible to common fungal diseases and environmental stresses. Fungal issues like Anthracnose and various leaf spots may appear during periods of high humidity, causing brown spots on the foliage. These are not life-threatening and can be managed by ensuring proper air circulation through pruning and watering at the base of the tree rather than overhead.
Environmental stressors are more common, with browning and wilting leaves indicating improper water management. Over-watering, especially in poorly draining soil, can lead to root rot, while prolonged drought can cause the leaves to scorch. The tree’s wood is naturally resistant to many wood-boring pests due to its tannin content. However, young saplings can be vulnerable to general leaf-eating insects, slugs, and snails. Additionally, the flower buds are prone to late-season frost damage, which can eliminate the spring bloom display.