Story and photos by Cene Ketcham, Extension Arborist, Casey Trees
Hophornbeam (Ostrya virginiana) is an attractive small to medium tree with big urban credentials. However, compared to other urban-tough trees like red maple, ginkgo, and honeylocust, hophornbeam has been regrettably underutilized.
Sometimes called “ironwood” like its bottomland cousin, Carpinus caroliniana, hophornbeam’s hard, dense wood makes it highly resistant to damage from wind, snow, and ice. Largely insensitive to site conditions, it takes indignities like air pollution, compacted soils, and droughty conditions in stride. Hophornbeam grows well in full sun to part shade, needs little pruning, and is generally free of insect pests and diseases. An excellent street tree in warmer climates, hophornbeam is intolerant of salt so should be avoided where road salting is common.
Regal Prince is the trademark name for Quercus x warei ‘Long’, a narrow, upright hybrid of fastigiate English oak (Quercus robur f. fastigiata) and swamp white oak (Quercus bicolor). Its leaves are clearly intermediate in shape and are glossy and leathery like those of swamp white oak. In Ithaca, Nina Bassuk and Andy Hillman first planted Regal Prince in 2005, and the oaks have performed well there ever since.
“It’s a good tree for tight spaces—not a shade tree as such,” says Cornell Urban Horticulture Institute Director Bassuk. “It has the shape of the fastigiate English oak but is more tolerant of poor drainage and is mildew resistant, unlike Q. robur. It also tolerates a higher pH than does straight Q. bicolor. During last summer’s drought its foliage stayed green throughout so it appears both wet and dry tolerant (after establishment of course).”
Some blog posts resonate long past their original publication date date. Transplanting and a Deeper Look at “Fall Hazards” was one of the top five posts in 2015 and was the second most viewed post in 2016. Former NYC Director of Street Tree Planting Matt Stephens and Taking Root Editor Michelle Sutton coauthored this story questioning commonly held beliefs about “fall hazards,” mostly as it applies to B&B trees, but they also discuss the interaction of the fall season with other production methods, like bare root. Nina Bassuk helped craft the section called “The Five Branches of Transplanting Success,” which should be of interest to anyone planting trees.
Kristy King and NYC Forest Restoration: Dreaming Big for the City’s Natural Areas Many readers wanted to learn about the work of the NYC Natural Resources Group, which manages 5,000 acres of forested natural areas across the five boroughs of NYC, and about Director of Forest Restoration Kristy King. Her dream for NYC: “… that all forested areas are dominated by native species and that invasive species have been managed to the point that natural forest regeneration is occurring and that the public holistically values the natural resources in their area.”
NYSDEC Urban Forestry Intern Jennifer Kotary: Get to Know Her! Many blog readers were keen to know about this dynamic up-and-comer. “My internship research involved in-depth exploration of what communities are doing to protect and build green infrastructure across the state. Via Mary’s [Kramarchyk] assigned projects, I was able to produce tangible evidence that there is quite the statewide collective will to plant and nurture an expanding canopy as well as many career and volunteer opportunities to do so.”
SMA’s 2016 Urban Tree of the Year: Musashino Zelkova generated a lot of buzz. ‘Musashino’ has been a successful and popular street tree for many more years in Japan, proving itself useful as a narrow, upright form of zelkova. It can tolerate drought and heat and is pH adaptable and pollution tolerant. See a list of all the past SMA Urban Trees of the Year here.
Gary Raffel: Get to Know Him! Gary has served the Council in a variety of capacities, including as a board member. “I started Dynamic Tree Systems in 2002, offering general tree care service as well as Plant Health Care and Integrated Pest Management programs. I later wanted to find a niche in the industry and purchased a Tree Radar Unit at a time when there were only three of us in the U.S. and eleven people in the world using the equipment. A few years later I became the company’s international trainer, such that when a new unit was sold I would fly to the particular client and spend a week training them on their new equipment (I still do that, in addition to Dynamic Tree Systems).”
The 2017 Society of Municipal Arborists Urban Tree of the Year is native to much of the Eastern United States. Hikers from New York to Tennessee who ascend to dry ridges will often see the deeply furrowed, blocky barked trunks of chestnut oak (Quercus montana) (syn. Q. prinus). The bark is so distinctive, it may be the only ID feature one needs.
There’s growing interest in using chestnut oak in the urban environment because it is pH-adaptable, handles dry soils and periods of drought, has a beautiful mature form, requires minimal pruning, and tends to be free of major pests and diseases.
The common name “chestnut oak” owes to the leaves looking like those of American chestnut (Castanea dentata) and indeed both are members of the beech family, Fagaceae. Other common names for chestnut oak include rock oak, rock chestnut oak, or mountain oak—referring to its customary sighting in dry, rocky soils on ridgetops, where it has a competitive advantage. However, if chestnut oak is open-grown in the moist, well-drained soil that all trees dream about, it will be significantly bigger than its scrappy ridgetop cousins. Typically it reaches 50 to 70 feet (15 to 21 m) tall and almost as wide. It’s hardy in USDA Zones 4 to 8 and prefers full sun.
The Society of Municipal Arborists (SMA) has voted Zelkova serrata ‘Musashino’ the 2016 Urban Tree of the Year. The yearly selection must be adaptable to a variety of harsh urban growing conditions and have strong ornamental traits. It is often a species or cultivar considered underutilized by urban foresters. The SMA Urban Tree of the Year program has been running for 20 years, and recent honorees include yellowwood (2015), ‘Vanessa’ parrotia (2014), and live oak (2013). You can see the full list of past winners on the SMA website, www.urban-forestry.com.
Zelkovas are native to Japan, Korea, and Taiwan. J. Frank Schmidt & Son Co. introduced Zelkova serrata ‘Musashino’ to the North American nursery trade in 2000. Named after a city in Tokyo (which itself is a city but also a prefecture containing multiple other cities), ‘Musashino’ has been a successful and popular street tree for many more years in Japan, proving itself useful as a narrow, upright form of zelkova. It has the genetic potential to reach 45 feet (14 m) in height and 15 feet (4.6 m) in width at maturity. It is hardy in USDA Zones 5 to 9.
… and it’s one that’s close to our hearts, in the sense that the Tree of the Year (TOY) is none other than the one featured in bloom in our blog’s banner up top, yellowwood (Cladrastis kentukea). What serendipity!
Surrey, BC Urban Forester Emily Hamilton, who attended NY ReLeaf last summer at Hofstra before she relocated to Canada, wrote a column earlier this year in City Trees about yellowwood. Hamilton wrote:
Like me, you may have a dog-eared, well-worn copy of the Urban Horticulture Institute’s (UHI) Recommended Urban Trees: Site Assessment and Tree Selection for Stress Tolerance. Another fantastic resource for urban foresters and UF volunteers that has just been updated is the Cornell Woody Plants Database.
Nina Bassuk says, “What makes the site unique is its focus on matching woody plants to site conditions, a feature sometimes lacking on other plant selection sites and a consideration that is sometimes lost in the design and plant selection process.” With its extensive image collection and cultural information, the site is also very useful for woody plant ID and study.
Each entry includes ultimate size and shape, USDA Hardiness Zone, light requirement, salt tolerance, moisture tolerance range, insect and disease considerations, and key ornamental features. Impressively, each entry has Nina voicing a short audio lesson that reinforces ornamental and ID features. Nina says this is a work in progress, as she is re-recording some of the entries for better audio quality.
There is a Course Plant Walk section, which you can use to find a series of plant walks through the beautiful Cornell campus based on different criteria like species (e.g., oaks, maples, and rosaceous and flowering trees) or tolerances (e.g., dry site and wet site trees); click on Maps to see the walk route.
The database was originally the outgrowth of the year-long joint Horticulture/Landscape Architecture (LA) course, “Creating the Urban Eden,” taught by UHI Director Nina Bassuk and Dept of LA Chair Peter Trowbridge.
The site had modest beginnings as an “online textbook” circa 2000. The first version consisted of a FileMaker Pro database running on the Cornell network from a Mac under a desk in the main offices of the Department of Landscape Architecture. Since then, the site has grown significantly more sophisticated with three major revisions that added additional features and functionality. The most recent upgrade was supported by a SUNY Innovative Instruction Technology Grant in 2013.
During her 2014 New York ReLeaf Conference plenary talk, Urban Horticulture Institute Director Nina Bassuk lifted up some underutilized trees for urban use. One of them, American smoketree (Cotinus obovatus) was growing just outside the conference room doors on the Hofstra University campus, where a mature specimen stood protectively behind a newly planted youngster. American smoketree is native to the U.S. South and Midwest.
Naturally and by training, American smoketree has a more tree-like habit than European smoketree (C. coggygria), and it matures up to 30 feet (9 m) tall and 20-30 feet (6 to 9 m) wide—twice as big as C. coggygria. It is hardy to zone 4 or 5, depending on which reference you consult. It is deer resistant and tolerant of drought and poor soils but doesn’t like to have wet feet for prolonged periods. Missouri Botanical Garden voted it one of its “Tried and Trouble-Free” tree species.
As part of her plenary talk at the 2014 ReLeaf Conference at Hofstra, Urban Horticulture Institute Director Nina Bassuk held up some underutilized trees that have worked well for her in Ithaca’s urban environs. Among them was ‘White Shield’ Osage orange (Maclura pomifera). In future posts we’ll cover others she recommended, like American smoketree (Cotinus obovatus).
‘White Shield’ Osage Orange
‘White Shield’ is the most readily available cultivar of Osage orange (Maclura pomifera) on the market. Although Osage orange is native to Oklahoma, Arkansas, and Texas, it grows readily beyond its native range. Because of the thorny nature of its juvenile (non-fruiting) stems, it was used as a natural fence for keeping in livestock. By hedging the tree, the juvenile, thorny form is perpetuated. In Ithaca, there is a remnant of such a hedge right in the middle of a residential neighborhood.
Osage orange is dioecious, meaning that male and female flowers form on separate trees. This is important because the fruits on female trees are enormous, about 6 inches (15 cm) in diameter. They are a conglomerate of beautiful green seeds and fruit that hangs on the tree until ripe in early fall. They then fall to the ground and could cause injuries and property damage, not to mention the mess. I’ve heard it reported that the fruits repel cockroaches and were sold in urban greenmarkets as a natural insecticide.
Luckily, male (fruitless) cultivars like ‘White Shield’ are readily available. ‘White Shield’ is an exceptionally fast-growing form once established. Branches are distinctly upright with glossy green leaves. Another especially beautiful cultivar is ‘Wichita’, selected by the late John Pair. Both of these selections originate from Oklahoma.
Osage orange has a lot going for it as a tough urban tree. Once established, it tolerates very droughty, windy, and hot sites. It can handle a wide range of pH, including highly alkaline soils, and is purported to be tolerant of wet conditions as well. It can also tolerate salt spray. It has no serious pests, and transplants easily. It matures at 20 to 40 feet (6 to 12 m) tall and similar spread.
It is considered hardy to Zone 4a; however, we have occasionally noticed some twig dieback perhaps due to failure to harden off sufficiently before winter in our zone 5. It readily grows out of the dieback during the following summer. Fruitless cultivars of Maclura pomifera like ‘White Shield’ are definitely worth a look. —Nina Bassuk, Director of the Cornell Urban Horticulture Institute
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