Each year, members of the Society of Municipal Arborists (SMA) vote for the SMA Urban Tree of the Year. Praise for this year’s winner, American hophornbeam (Ostrya virginiana), came from fans in states as far-flung as Wisconsin, New York, Virginia, and Texas.
Here, we hear from the Council’s Dr. Nina Bassuk at Cornell and from her colleague, Dr. Eric Wiseman at Virginia Tech. You can see the full list of SMA Urban Trees of the Year going back to the program’s inception in 1996 here.
Nina Bassuk, Director of Cornell’s Urban Horticulture Institute: Ostrya virginiana has common names that include American hophornbeam, Eastern hophornbeam, hornbeam, ironwood, leverwood … a poster child for why common names can be a problem! This is a medium-sized tree in the birch family that has a very large native range east of the Rockies, from Manitoba to Florida.
Ostrya can be found most often as an understory tree and is distinctive for its bark, which looks like thin, evenly spaced stringy strips lightly exfoliating from the trunk. When we urban foresters bring it out of the forest and onto the street, it makes a generally oval to rounded tree, about 30 feet (9.1 m) tall at maturity, with somewhat downward drooping branches. The distinctive hop-like flowers that give Ostyra its common name are most numerous when it has some sunlight, but the tree grows well in light shade, too.
Although it manages dry periods in the shade of the forest, it is not particularly drought-tolerant on the street. However, we at the Urban Horticulture Institute (UHI) have found that it tolerates a wide soil pH range and is pest-free.
Our UHI research on transplantability of Ostrya virginiana agrees with others that it is difficult to transplant successfully. In our study, small-caliper (1.5 inch/38 mm) trees showed significant transplant shock in the first year after planting but then recovered in their second year. B&B trees transplanted better in the spring than bare root trees, while B&B and bare root trees transplanted equally well in the fall. Regardless of production method or season, small-caliper trees would be recommended when transplanting. — NB
Eric Wiseman, Associate Professor of Urban Forestry, Virginia Tech: Perhaps the most humble member of the birch family (Betulaceae), American hophornbeam (Ostrya virginiana) may not be as flashy as its white-barked cousins. But for those familiar with this denizen of temperate deciduous forests in eastern North America, the beauty of the species lies in the subtlety of its ragged grayish-brown bark and the intricacy of its papery composite fruit resembling the hops that flavor our favorite adult beverages.
For arborists, the attraction of hophornbeam goes beyond its outward appearance, for it fills a gap in the plant palette where few other native species have similar traits. It is a fairly slow-growing, shade-tolerant species that, here in Virginia, reaches an intermediate stature of 30 to 40 feet (9.1 to 12.2 m) at maturity. It is hardy in zones 3 through 9A and is known to tolerate poor soil conditions, provided soil drainage is adequate. This makes it a good candidate for planting in narrow tree lawns, sidewalk cutouts, and parking lot buffers throughout most of the conterminous United States and southern Canada. On the Virginia Tech campus in southwest Virginia, hophornbeam was the tree of choice for an outdoor dining area on the south side of Squires Student Center where both above- and below-ground space were at a premium, yet shade and ambience were for critical to diners’ comfort.
Known for its strong wood, hophornbeam also naturally takes on an excurrent growth habit with well-spaced, subordinate scaffold branches. As such, it requires minimal structural pruning and holds up well in storms and busy urban environments. Given its slow growth rate, transplanting and aftercare require attention and patience. But once established, hophornbeam has few serious pest or disease problems.
If you are looking for a tough native tree with subtle ornamental flair, you might want to incorporate a few hophornbeam into your next planting project in the urban forest. — EW
The SMA 2019 Urban Tree of the Year designation recognizes the underutilized, attractive, and useful American hophornbeam (Ostrya virginiana) for its service to urban forests and encourages its use when matched appropriately to site and as part of a diverse urban tree inventory.