by Michelle Sutton

The Council’s beloved Dr. Nina Bassuk (who prefers to go by “Nina”) will formally retire from Cornell at the end of this August (2022). When the world’s foremost authority on street trees and urban forestry retires after 42 years, there’s significant anxiety among those of us who have benefitted so greatly from her work, even as we are happy for our colleague and friend. Will her vital Urban Horticulture Institute research continue, and if so, in what areas?

“I’ve been reflecting on this decision for about a year,” Nina says. “I will probably move to Emeritus status, which means I’ll maintain a small office on campus and continue some selective research and limited extension activities. I won’t be teaching anymore, and I won’t have graduate students or undergraduate advisees after my most recent MPS student, Caroline Stokes, completes her degree.”

Nina has advised nearly 60 graduate students and as many or more undergraduates since she started teaching and founded the Urban Horticulture Institute at Cornell in 1980; she still receives on average two requests a week from students who would like to study with her.

Nina teaching Creating the Urban Eden students about root architecture and proper tree planting techniques.

There is a lightness in her voice as she spoke of the impending change. “Teaching the [two-semester] Creating the Urban Eden class was a big deal,” she says. “I tailored my approach to the composition of each incoming class and was always looking for ways to engage them and keep things fresh for them and for myself. It was important for me to convey that the skills they were learning—in site assessment, site preparation, plant selection, etc.—would position them uniquely among their peers without those skills. All that’s to say, I put a lot of effort into teaching. So I guess there’s lightness in my voice because there’s space opening up in my life to do other things. Still, it’s bittersweet for me, this change, because I’ve loved teaching.”

The Urban Horticulture Institute (UHI) at Cornell was founded in 1980 by Nina. As she describes it, it’s always been a program area, a locus for research, and an idea, rather than a physical place. Since the School of Integrated Plant Science (SIPS) is not refilling Nina’s professorship or UHI Director position, she will continue running UHI in her emeritus status for the foreseeable future.

Nina, Barbara Neal, Bryan Denig, and Yoshiki Harada had a professional peak experience when they were hired to evaluate the condition of the National Mall elms and develop a landscape plan for their gradual replacement with a more diverse, sustainable, and climate resilient inventory. Photos by Yoshiki Harada

Nina measuring soil compaction with a penetrometer on the National Mall.

Through her ongoing UHI research, Nina is looking forward to more time to pursue her propagation-related research interests; this has been an abiding interest since she earned her doctorate from the University of London in 1980 in Plant Propagation. Readers may be familiar with Nina’s 25-year hybrid oak propagation work, and some readers have UHI hybrid oaks planted out for trialing in their communities.

“Out of the numerous hybrid oaks that were developed in 2004-2006, we have found about three or four particularly good ones that we have started to propagate via tissue culture,” Nina says. “However, the ‘recipe’ for success with these hybrids tends to be genotype specific; each hybrid needs slightly different conditions to multiply and root. Micropropagation of oaks has never been consistently successful, but after many years and the efforts of many students and technicians, we’re seeing some light at the end of the tunnel.”

Nina says she really enjoys the challenge of working out techniques to propagate species that aren’t freely available in the trade because people have found them so hard to propagate. Like hickories, for instance. The same process that she and her team developed for the hybrid oaks, they’re now applying to hickories. “They have great potential for urban use because they tolerate heat and both wet and dry extremes, so they have resilience to climate change,” Nina says. “They have food value for people and wildlife, and they have beautiful fall color. But right now, you can’t get them in nurseries because of the propagation barriers.”

Shellbark hickory (Carya laciniosa) is one of the hickory species for which Nina is most excited to develop successful propagation techniques. Wikimedia, Douglas Goldman, USDA CC BY-NC 4.0

Nina and recent doctoral candidate Brandon Miller have started with shagbark hickory (Carya ovata), but once they “crack the code” for that species, they want to apply what they learn to propagating other useful and beautiful hickories, like pignut hickory (C. glabra), mockernut (C. tomentosa), bitternut (C. cordiformis), true pecans (C. illinoinensis), and a species that Nina in particularly enamored of, shellbark hickory (C. laciniosa), also known as kingnut. “Shellbark hickory is such a beautiful tree, with sweet nuts, shaggy bark, and the ability to tolerate periodic flooding and drought,” she says. “In its native range, it’s usually found in wetlands.”

When Nina and Brandon used layering, etiolation, and rooting hormones to propagate shagbark hickory by cuttings, they were surprised and delighted that tweaking the amount of IBA (indole-butyric acid) provoked the plant to develop fibrous root systems. (Hickories famously have a strong tap root system, which can make transplanting a challenge, so that if nurseries sell hickory at all, they sell small, rooted seedlings.)

“We went into that first phase of research thinking some individual shagbark hickory individuals might be easier than others to propagate, but producing fibrous roots—that was totally unexpected,” Nina says. Overcoming tap root formation/producing fibrous roots could be the key to successful propagation, which means getting saleable-size hickories into the trade. The next step for Nina and Brandon is to compare seedling (sexually propagated by nuts) hickories to layered (asexually propagated by layering) hickories to see if the latter have better water uptake and better transplanting success.

Nina is also looking forward to continuing her own work on propagating unusual shrubs, ones that you don’t often see in nurseries because they are hard to propagate. She’s working on white forsythia (Abeliophyllum distichum), which blooms two weeks before forsythia and is quite fragrant. She’s also working on Chinese fringetree (Chionanthus retusus) and white fringetree (C. virginicus), both extremely difficult to propagate. She would also like to find a way to successfully propagate spicebush (Lindera benzoin). “My graduate student, Caroline Stokes, has had good success rooting spicebush,” Nina says. “The goal is to propagate desirable plants for greater availability in the trade.”

“White fringetree (Chionanthus virginicus) [depicted] is exceedingly difficult to propagate,” Nina says. “I would really like to figure this one and Chinese fringetree (Chionanthus retusus) out so they can be more readily available in the trade.” Photo by Michelle Sutton

As much as plant propagation and tree selection for stress tolerance has been a major feature of Nina’s work, the issue of soil remediation is equally if not more important to her. Urban soils are commonly degraded and compacted so that no tree, no matter how tough, will grow well without intervention. Moreover, soils under pavement require compaction to bear the weight of pavement. To meet this challenge, she and colleagues developed CU-Structural Soil, a soil that is made to be placed under pavement to meet engineering specification for load-bearing—while allowing tree roots to grow through it. CU-Soil has been used by about 2500 communities all over North America. There is still more research to do on the potential addition of biochar to CU-Soil to increase its water holding capacity; this work is ongoing.

A technique Nina and colleagues developed for remediating compacted soil wherever soil doesn’t have to support pavement, called “Scoop and Dump” or “Amend Soil in Place,” has proven itself in research and application. “After urban development, soils are generally trashed,” Nina says. “By adding about a third by volume of compost and deeply incorporating it to about 18 inches, soil compaction is eliminated and continues to be improved over time. This has been used on the Cornell campus for the last 20 years and the long term-results are impressive.” Nina hopes to write a bulletin describing this technique to practitioners and communities.

Nina at NY ReLeaf in 2018 in Rochester, with (left to right) Berna Ticonchuk, Susan Maney, Jim Kisker, and Keith Miller.

Nina and her husband, the landscape architect Peter Trowbridge, also retired from Cornell, continue to spend as much time in their gardens as possible. They have 10 acres of designed space, filled with trees and shrubs, some perennial gardens, beautifully designed vegetable gardens and fruit orchards, a pond, a high-tunnel greenhouse, tidy farm building ruins, rock walls and now—a micropropagation lab. Their daughter Sophie and her husband Ryan live in the adjacent building that used to house Peter’s landscape architecture group practice; it’s since been converted into Sophie and Ryan’s home. Ryan brings a background in micropropagation with a special interest in carnivorous plants, especially the Nepenthes genus. Nina and Peter intend to help out with the business.

“These days, Peter and I do our gardening for half a day, in the morning,” Nina says. “Right now we’re anxiously watching the fig trees that occupy part of the high tunnel, hoping that the hundreds of green fruits will ripen.” (Some years they do, some years they don’t). “We like to eat them right off the plant—if they ripen,” she says, laughing. “They don’t love Ithaca’s winters … so we did finally add heat to the high-tunnel greenhouse so that the temperature doesn’t go too far below 40 degrees in the winter; that should help the fig ripening situation.” Nina says that like so many horticulturists, she and Peter can’t resist a hardiness-zone-defying challenge.

“After traveling so much for so long, I would like to do considerably less traveling,” Nina says. I do go to NYC and back, including visiting my daughter Cory on Long Island. That’s all the traveling I want to do for now, except that I’d like to see our good friends in England, friends from my grad school days. I’m looking forward to more time to play music, which was my passion and training even before horticulture. I play piano and flute; the latter’s been on hiatus for awhile, so I’d like to explore a way to play more regularly. I enjoy reading good fiction—it’s got to be page-turning—and am eager to have more time for that.”

Nina takes special pride in the Cornell Woody Plants Database and hopes readers will take advantage of this resource. The UHI website will also remain up, and Cornell Landscape Architecture Assistant Professor Jamie Vanucchi will teach a scaled-down version of Creating the Urban Eden. New York State Urban Forestry Council members will be glad to hear that Nina plans to remain a Council Board Member. ♦