One of the signs of Spring on our Master Gardener hot line is the question “What are those lovely purple-flowered trees we see along the highways?”
There are really two possibilities, the most likely being the Princess Tree, Paulownia tomentosa. This tree can quickly grow to as much as 60 feet and is not at all demanding as to moisture or soil. That’s why we typically see it in locations where the soil has been disturbed and little else is growing.
Paulownia flowers are borne on erect panicles that grow upward. Each of those flowers produces a capsule that contains literally dozens of light, winged seeds that are widely disbursed by the wind. That explains how they reach high on the cliffs in the rocky gorge of I-40 west toward Tennessee, for example.
Not only does the question arise on the Master Gardener helpline! Apparently it is a frequently asked question of the staff of the NC Welcome Center along I-40. Prominently displayed on the doors of the welcome center are signs that tell what they are and that they are not native to NC.
The flowers of the other possibility hang downward in showy clusters and that’s an oriental Wisteria, Wisteria sinensis. This is a vine but when it climbs and envelops a tree it can easily be confused with Paulownia, being about the same shade of violet or purple. Your answer then is to check the arrangement of the flowers. Growing upward equals Paulownia, hanging down, Wisteria.
Paulownia, by the way, is the “Miracle Tree” you see advertised for its flowering beauty, rapid growth and tough constitution. However it really doesn’t make a good landscape tree as It has weak branches and produces a lot of litter as leaves and seedpods scatter later on. Both, Paulownia tomentosa and Wisteria sinensis, are listed by several states and the US Forest Service as being invasive, definitely not the kind of plants you want to bring home to meet the family.
Article written by Glenn Palmer, Extension Master Gardener Volunteer.