For Seth Wannemuehler, Assistant Professor and the new lead of the Woody Ornamental Breeding and Genetics program in the Department of Horticultural Science, a career in plant science wasn’t immediately obvious, but there were some early indications. Something clicked for Wannemuehler at his first job mowing grass at a local cemetery in Evansville, Ind. He loved spending his days outside on the riding lawn mower, and even mowed lawns for family on the side, including his grandparents, who had a victory garden, made wine and pickled vegetables.
Though he started college as a pharmacy student, he quickly transitioned into the plant science department at Purdue University to study botany, plant pathology and horticulture, and worked during the summers at a local nursery where some of the first plants he sold were azaleas from the University of Minnesota Lights series.
“The idea that we could grow these tropical-looking, exotic plants in the north was so cool,” said Wannemuehler, adding that his job at the nursery first sparked his love of ornamental plants.
After college, Wannemuehler headed further north to the University of Minnesota, where he completed his master's and doctoral degrees under the mentorship of Jim Luby, studying fruit breeding economics and later kiwiberry, before moving into landscape plants and walnuts as a postdoctoral associate in Brandon Miller's lab.
Now, Wannemuehler is at the helm of the Woody Ornamental Breeding and Genetics program, which has released many popular cold-hardy roses, ornamental shrubs, and the iconic Lights series of azaleas beloved by cold-climate gardeners.
Steve McNamara, Project Scientist at the Horticultural Research Center (left); Assistant Professor Seth Wannemuehler (center); and Emeritus Professor Stan Hokanson, former lead of the Woody Ornamental Breeding and Genetics Program (right) at the Horticultural Research Center.
Cold-hardy, tropical color
Developed at the Horticultural Research Center (HRC) at the Arboretum, these cold-hardy flowering shrubs bloom in late May and early June in shades of pink, fuchsia, white, orange and yellow, and can be found in gardens and collections across the Arboretum.
Azaleas have been a focus of research at the HRC at the Arboretum since the 1950s and represent the decades-long collaboration between the Arboretum and the Department of Horticultural Science.
In 1957, researcher Albert G. Johnson developed the first azalea bred specifically to tolerate Midwestern winters. By crossing Rhododendron prinophyllum (the roseshell, or early azalea, native to North America) with the Asian hybrid Rhododendron × kosteranum, Johnson developed a new variety of azalea that could tolerate temperatures as low as minus 30 degrees Fahrenheit. This new azalea hybrid was first released to the public in 1978 as the cultivar Northern LightsTM, establishing the University of Minnesota as a leader in deciduous azalea breeding. Today, the Lights series of azaleas includes 15 different cultivars.
The Azalea Trial Garden is a highlight for azalea viewing at the Arboretum in the spring.
Future of the breeding program
While the Lights series of azaleas gave cold-climate gardeners a broad range of colors to choose from, Wannemuehler hopes to develop azaleas that are resilient to the changing climate and meet gardeners’ evolving needs.
Today, plants need to not only tolerate Minnesota’s cold winters but also handle unpredictable temperature fluctuations in the fall and spring that can cause plants to break dormancy, leading to damage. “Cold hardiness is the baseline for these plants; now, we’re layering on resiliency for the unpredictable shoulder seasons,” said Wannemuehler.
Wannemuehler also sees an opportunity to introduce better azaleas for consumers by breeding cold-hardy evergreen azaleas that keep their foliage throughout the winter, and by developing azaleas with high pH-tolerant rootstock. Most azaleas and rhododendrons require acidic soil with a pH between 4.5 and 6 to flourish, which might deter low-maintenance gardeners.
Whatever new releases Wannemuehler and team develop, it will be a while before they reach gardeners. It takes about 15 years from start to finish for one introduction to reach the public!
Visitors can find University of Minnesota-developed azaleas growing alongside lilac, Eastern redbud, maples and more in the Japanese Garden.
When and where to see azaleas at the Arboretum
Azaleas bloom in late May and early June. Some of the best viewing spots to see azaleas at the Arboretum include the Woodland Azalea Garden, the Bailey Shrub Walk and the Azalea Trial Garden, located between the Maze Garden and the Pine Collection on Three-Mile Drive, where new and previously released plants are evaluated by the breeding program.
According to Wannemuehler, one underrated stop for azalea-viewing is the Bonita and Scott Fisher Japanese Garden, located near the Oswald Visitor Center, where the vivid colors of azalea blooms stand out against the lush, green foliage in the springtime.
But the Azalea Trial Garden holds a special place in his heart. In addition to being the home of azalea breeding at the Arboretum, it’s also where he was proposed to in May 2024.