Empress tree (Paulownia tomentosa) is a deciduous fast-growing tree native to East Asia. It is widely cultivated as an ornamental because of its favorable growing qualities and big clusters of showy purple flowers. Due to its fast-growth, vigor, and adaptability, empress tree has become an invasive species in certain countries.
I. Appearance and Characteristics
Paulownia tomentosa, common names princess tree, empress tree, or foxglove-tree, is a deciduous hardwood tree in the family Paulowniaceae, native to central and western China. It is an extremely fast-growing tree with seeds that disperse readily, and is a persistent exotic invasive species in North America, where it has undergone naturalization in large areas of the Eastern US. P. tomentosa has also been introduced to Western and Central Europe, and is establishing itself as a naturalized species there as well.
This tree grows 10–25 m (33–82 ft) tall, with large heart-shaped to five-lobed leaves 15–40 cm (6–16 in) across, arranged in opposite pairs on the stem. On young growth, the leaves may be in whorls of three and be much bigger than the leaves on more mature growth. The leaves can be mistaken for those of the catalpa.
The very fragrant flowers, large and violet-blue in color are produced before the leaves in early spring, on panicles 10–30 centimeters (4–12 in) long, with a tubular purple corolla 4–6 centimeters (1+1⁄2–2+1⁄4 in) long resembling a foxglove flower. The fruit is a dry egg-shaped capsule 3–4 centimeters (1+1⁄8–1+5⁄8 in) long, containing numerous tiny seeds. The seeds are winged and dispersed by wind and water. Pollarded trees do not produce flowers, as these form only on mature wood.
Paulownia tomentosa requires full sun for proper growth. It is tolerant of pollution and can tolerate many soil types. It can also grow from small cracks in pavements and walls. Paulownia can survive wildfires because the roots can regenerate new, very fast-growing stems.
Unfortunately, the empress tree is appealing to look at, but it is not good for your landscape, property, environment, or local ecosystems.
At first, the tree smells heavenly, like vanilla, and the tree blooms with thousands of flowers in the form of foxgloves every late April and early May. But this seeming benefit of the tree is actually its greatest drawback: the fruit on each of those flowers hold 2,000 seeds, with a single tree capable of casting 2,000,000 seeds a year. Additionally, the empress tree can grow 20 feet in a single year. The potential for the tree to become invasive is tremendous, and the potential for it to take over a landscape if you fail to remove a stray seedling is just as high.
II. How to Grow and Care
Sunlight
In order to achieve the full amount of blooms you will want to give your empress tree full sun, at least 6 hours of direct sun a day. If you are not worried about getting profuse flowering it will tolerate partial shade without any negative effects.
Temperature and Humidity
Empress trees are hardy. Very hardy. They can withstand temperatures from -10 degrees Fahrenheit high and temperatures up to 120 degrees Fahrenheit, but these temperatures are deceiving. The tree is actually a lot less tolerant than these numbers express. The empress tree’s roots are hardier than its stems. Flowers and leaves will die at 0 degrees Fahrenheit, and the entire trunk will die at -10 degrees Fahrenheit if the cold lasts more than a short time.
Watering
The tree is pretty darn near indestructible once established, but it does require some care, including ample watering. After planting the tree, be sure to mulch two to three inches deep out to the drip line without touching the trunk to help retain moisture. You will want to water it weekly at a rate of two to three gallons of water per inch of its trunk diameter. Carry on with this regimen during the first season until autumn. Further supplemental watering shouldn’t be needed going forward.
Soil
Ideally, its preferred soil is moist and rich, but it will grow in almost any condition. It has been known to grow in sidewalk cracks, uncleaned rain gutters, sandboxes, and firepit ash, so there’s no real need to fuss about the soil conditions too much with the empress tree.
Fertilizing
While empress trees do not usually require much fertilization, top-quality specimens can be produced by adding ammonium nitrate, superphosphate, and potassium phosphate when planting. Subsequently, a balanced N-P-K fertilizer can be added to the soil every few weeks.
Planting Instructions
Pruning
Taking on this chore can be a matter of preventing property damage and trying to manage the insanely fast growth. You will want to clear branches that may be susceptible to snow or wind damage or present hazards.
But be careful when pruning: empress tree wood is notoriously weak, and making poor cuts and using improper pruning technique can lead to further weakening the wood.
When trying to control the empress tree’s aggressive growth, numerous techniques are employed depending on the desired result. To curb the growth and keep the tree a manageable size, you will want to cut your tree down to about five feet every autumn. Doing this will allow the tree to grow back and bloom every spring.
If rather than having blooms you’d prefer to have an interesting shrub with fascinating foliage 36 inches in width, cut just above the ground level. Doing this will not let flowers or fruit appear but will create some spectacular foliage.
Propagation
Pests and Diseases
The empress tree doesn’t have any serious pest problems, though slugs and other insects may nibble on the leaves. Fungi can infect the tree and cause stem canker, and is best treated by an arborist. Planting the tree in a good site and keeping it in good health should deter any fungal infections.
Maintenance
- If you want your Empress tree to produce the maximum number of blooms, you will need to position it in a location where it receives at least six hours of direct sunlight every day.
- If you are not concerned about the plant producing an abundance of flowers, then you can place it in partial shade without any adverse effects.
- They are most successful when grown in a location that receives a lot of direct sunlight, has a somewhat warm climate, and has rich soil that is kept slightly damp.
- They are highly voracious plants, therefore their growth will match the rate at which they are nourished in rich soil with more compost or manure.
- The plant has been observed to grow in sidewalk cracks, uncleaned rain gutters, sandboxes, and campfire ash, which means that there is no actual need to stress over the soil conditions too much with the empress tree.
- Roots are tougher than the stems of the empress tree. Flowers and leaves die at 0°F, and the trunk dies at -10°F if the cold lasts long enough.
III. How To Get Empress Tree To Bloom
Poor sun exposure, pruning heavily, or pruning at the wrong time of year can affect your tree’s flowering. Increase light exposure if your tree was planted in shade. Limit pruning to right after blooming has finished in spring, or prune lightly.
IV. Uses and Benefits
Paulownia tomentosa is cultivated as an ornamental tree in parks and gardens. It has gained the Royal Horticultural Society’s Award of Garden Merit.
Because of its tolerance and flexibility, Paulownia functions ecologically as a pioneer plant. Its nitrogen-rich leaves provide good fodder and its roots prevent soil erosion. Eventually, Paulownia is succeeded by taller trees that shade it and in whose shade it cannot thrive.
The characteristic large size of the young growth is exploited by gardeners: by pollarding the tree and ensuring there is vigorous new growth every year, massive leaves are produced (up to 60 centimetres (24 in) across). These are popular in the modern style of gardening which uses large-foliaged and “architectural” plants.
The soft, lightweight seeds were commonly used as a packing material by Chinese porcelain exporters in the 19th century, before the development of polystyrene packaging. Packing cases would often leak or burst open in transit and scatter the seeds along rail tracks. The magnitude of the numbers of seeds used for packaging, together with seeds deliberately planted for ornament, has allowed the species to be viewed as an invasive species in areas where the climate is suitable for its growth, notably Japan and the eastern United States.
In Japan, it is customary to plant seeds of the tree when a couple has a daughter; it is said that by the time the daughter is in her older teens or at the peak of adulthood when she is ready to marry, the tree by this time has also grown to maturity, which is then felled and made into a tansu dresser as a wedding gift.
P. tomentosa has been suggested as a plant to use in carbon capture projects. P. tomentosa has large leaves that readily absorb pollutants, and also has value in timber and aesthetics, adding to interest surrounding its use in carbon capture.
