Holden Arboretum staff are available as expert spokespeople on a variety of botanical, horticultural and conservation issues. The listing below profiles some of Holden's experts, additional topics and staff are available.

Jennifer Hillmer, Land Steward

Not a native plant? Like to run wild though the woods? Jen will make sure your days at Holden are numbered. She specializes in protecting Ohio’s native plant communities, so beware your stay may be short-lived. What does she have against non-native invasive plants? Jen’s glad to tell you.   

Jen on invasive plants:

“Sometimes invasive non-native plants are used in landscaping without realizing the problems they may cause when they escape into natural areas. While they may look pretty, without natural predators or controls, invasive non-native plants are able to spread quickly and force out native plants.

Invasive plants can invade woodlands and displace native wildflowers. Native plant

diversity is important for wildlife habitat as many animals depend on a variety of native plants for food and cover. As native plants disappear, so does the wildlife.”

Ethan Johnson, Plant Records Curator

Ethan’s our resident “CPA” Certified Plant Accountant — but he’s no bean counter. 

In addition to cataloging our collections, Ethan also maps the grounds and collections, verifies the identity of new plants, curates the herbarium, and is a published writer. He’s also traveled the globe for botanical expeditions to Taiwan, China, and New Zealand to name a few. He’s an expert on so many things, it’s difficult to keep track of them all!

Ethan on plant collections:

“Holden’s themed plant collections present a larger selection of species and varieties within the scope of a single plant genus, family or functional group. They are intended to highlight diversity within each group and provide locations where the performance of uncommon species or new selections can be evaluated alongside familiar species and standard varieties.

Some of our more popular plant collections are our conifers, magnolias, and arborvitae and false cypress. Detailed records are kept concerning all plants in Holden's gardens and themed plant collections. We've also put them all on the web so visitors can identify whether a particular plant can be found at Holden.”

Steve Krebs, PhD, Director of Leach Research Station

Think “rhodies” only tour with rock bands? As director of the Leach Research Station, Steve can show you rhododendrons (rhodies) and azaleas that will rock your world. He can also give you the scoop on the genetic improvement of woody plants.

Steve on rhododendron research:

“Continuing in the legacy of Dr. David Leach, an eminent American horticulturist who became a world authority on rhodendrons, we are working to develop and introduce hardy hybrid rhododendrons for the gardening public. However, today, the traditional breeding program is complemented by a vigorous research component focused on adaptations of rhododendrons to biotic and abiotic stresses, such as winter freezing injury to leaves and buds, summertime 'bleaching' of leaves, and diseases caused by fungal pathogens. And while much of the research focus is on a rhododendron at the whole plant level, our findings are broadly relevant to other woody plant species.”

Brian Parsons, Director of Conservation

He knows all, he sees all. After almost 30 years at Holden, Brian knows the lay of the

land and how to preserve it better than anyone. Need an expert on everything from head water streams to wildlife management — he’s helped Holden achieve legendary status for water, wildlife and land conservation.

Brian on plant conservation:

“The Holden Arboretum displays and conserves rare Ohio plants designated by the Heritage Network, a program to protect rare Ohio plants. In 1997, thirty-five rare species were recorded on Holden property. These populations are monitored to see if they are increasing or decreasing, to see how successful changes in the environment alter the populations, and to calculate the percent fruit set and seed viability.

We are also the Midwest regional representative for The Center for Plant Conservation, a national organization dedicated to preserving rare and endangered plants throughout the United States, presently displaying 27 species of federal concern.”

Paul Spector, Director of Education

Connecting everyone from school children to seniors to over 3,500 acres of natural resources can be a daunting task. Leave it to Paul to handle the challenge and make learning about science and nature, fun, exciting, and easy. He’s so good; most people don’t even know they’re learning.     

Paul on people-plant connections:

“Education at Holden is designed to promote and enhance interest and knowledge about the environment and to engage people in programs about horticulture, botany, and natural history that utilize diverse learning experiences and that contribute to a process of life-long learning.

Our goal is to make a connection between people and plants, and that can be done in a variety of ways. Although we still offer traditional means such as hikes and horticultural classes, we've opened new avenues such as knitting in nature and yoga in the garden to reach different audiences.”

Mary Topa, PhD, Director of Science and Research

Did you ever wonder how trees can survive drought one year and flooding the next? Or even how trees can grow in soils that may be flooded all year round? Mary has spent most of her research career asking these sorts of questions. She’s discovered that trees are amazing organisms that modify not only their roots, but the soil around them in order to survive stressful soil environments.

Mary on urban forests:

“Holden’s initial research program focused on breeding superior woody ornamental plants for the landscape. However, Holden’s proximity to a large metropolitan area and the large acreages of contiguous natural areas make it ideally suited for studying the stress biology of urban forests. Urban forests and trees are subjected to multiple stresses that ultimately can diminish overall forest health and vigor, and increase their susceptibility to insect and pathogen invasions.

Studying how trees adapt to both natural and anthropogenic (man-made) stresses will help in the restoration of native biodiversity in some of the natural areas, and in the utilization of more sustainable practices in our gardens and collections.”

Charles Tubesing, Chief Horticulturist

He’s who plants come to when they want to know what they should be doing, when they should bloom, when they should drop leaves and when they should seed. Don’t play plant trivia with Charles. Because everyone knows if you’ve got a plant question Charles has your answer. 

Charles on sustainable landscapes:

“Holden acquires plants and places them into gardens and themed plant collections.

We collect and display a diversity of plants for evaluation, enjoyment and educational purposes, in order to convey sustainable plant choices recommended for our region.

By sustainable, we mean that the plants are adapted to our soil and climate, are free from chronic diseases and significant pests, and are non-invasive in nature.

We try to set good example for home gardeners, by showcasing plants in the right environment — they can take pretty much anything we've done here and adapt it to their own landscapes.”

Marian Williams, Manager of Public Programs

With over 200 species of birds residing on Holden grounds, it’s easy to mistake a woodpecker for a nuthatch. But not for Marian, she can ID everything from cardinals to chickadees. She can also ID the trees in which they reside. Holden, a tree museum and Important Bird Area, is a birder’s paradise.

Marian on birding:

“In 2004, Holden was identified as an ‘Important Birding Area’ by the National Audubon Society. We received this esteemed designation based on the diversity of habitats which Holden offers for resident, nesting and migrating birds.

We have birders from across the country visit us, as well as local enthusiasts — including our Junior Birders whose monthly hikes have yielded some extraordinary finds!”