Sunday, August 31, 2014

Hop hornbeam makes me happy

At the end of my first week at Kew, all the interns were taken to the library.  As Daisy and I walked toward the entrance of the building, one tree stopped me in my tracks.  The tree was completely draped with lacey white clusters of seed pods.  "What is that tree?" I asked Daisy, assuming it was an English native.  She didn't know, but I kept my eyes peeled for another specimen with a label.

Beautiful, showy seed clusters of Ostrya virginiana
resemble hops, thus the common name "hop hornbeam"
Later that summer I noticed another specimen growing in Kew's Duke's Garden.  The label identified it as Ostrya virginiana (1973-14189), more commonly known as ironwood or the hop hornbeam.  Imagine my surprise to learn that this tree is native to my region of North America, and then some.  Hardy to USDA zones 3 to 9, its range spreads as far north as Prince Edward Island and Manitoba, westward to the Dakotas, and as far south as Honduras. 

What the hop hornbeam lacks in flower luster, it makes up for in seed.  The green catkins aren't really that noticeable or attractive, but the seed pod clusters are very attractive and persistent.  These clusters resemble hops, which earn the common name "hop hornbeam".  The specimens at Kew have held their clusters from at least the last week of June until present.  The seed pods were a brilliant white at the end of June, fading to salmon, now with tinges of brown.  The seeds are a food source for wildlife including birds and small mammals.

View of the attractive clusters
from inside the tree
Although the tree is stunning in seed, it is also attractive in foliage.  The shiny green leaves resemble an elm or birch.  Fall foliage is yellow.  I've seen specimens with a very fine, gold fall color that persists for several days.  The autumn show may not be dependable and will vary by the environmental conditions.  According to the Missouri Botanical Garden plant finder website, "Leaves turn an undistinguished yellow in autumn and often drop early."

Ostrya virginiana is a slow growing, medium sized tree.  In most regions within its range, this tree won't get taller than about 40 feet.  There may be some exceptions, such as the 73 feet tall by 88 feet wide specimen discovered in Michigan in 1976.  But achieving such heights would take a great deal of time.  Its slow growth results in very dense, hard wood (thus the common name "ironwood").  However, this feature is not of much economic value because it would take such a long time for a stand to yield any harvest worthwhile value.  

Yet the slow growth, small stature, and strong wood makes this tree a valuable addition to a residential or commercial landscape situation.  Businesses and homeowners should consider substituting this underused strong, healthy native for the more common pest and disease prone Cornus florida or extremely weak-wooded and invasive exotic Pyrus calleryana 'Bradford'.

Despite the great potential for cultivating Ostrya virginiana in the urban environment, it has been classified as a "weed" by those who cultivate timber crops in some regions.  To quote a USDA Forestry report from 1990:

Attractive foliage
The slow growth and small size of the species earn it the title "weed" throughout its range, especially in some areas in the South where it is considered the number one weed species. Eastern hophornbeam usually is discriminated against in stands managed for timber. Silviculturally, more interest has been given to eradicating it than to improving its growth.

Perhaps the hop hornbeam is a bit weedy in stands of timber because it is so adaptable.  Ostrya virginiana has been found in soils that have acidity levels between 4.2 and 7.6 pH, and growing in elevations between 250 feet and 5,000 feet.  The hop hornbeam is also very pest and disease resistant, with few recorded issues.  One thing this tree won't forgive is wet feet.  In the wild, it is common in dry stream beds, bluffs, and even xeric conditions. 

Fall is approaching, and the upcoming cool season is a fantastic time to add woody trees and shrubs to any landscape (learn more by reading the tree planting post).  When considering what specimens do add to your garden, be sure to add the adaptable and beautiful Ostrya virginiana to the list. 

If you have any questions, comments or suggestions, please feel welcome to leave a comment or send me an email.

To see more photos from this week, be sure to check out the album "Hop hornbeam makes me happy" on the Plante on Plants Facebook page.  "Likes", shares and comments are appreciated.

Nice, open habit
Shaggy, peeling red bark
All photos and videos were taken by Amanda Plante at the Royal Botanic Gardens, Kew unless otherwise stated in the caption.

  • Center for the International Trade in Endangered Species database
  • "Ironwood or Hop Hornbeam".  N.D. Tree Handbook.  North Dakota State University.
  • Kew's Living Collections database
  • Metzger, N.F.  (1990).  "Eastern Hop Hornbeam".  Silvics of North America, Volume 2: Hardwoods.  United States Department of Agriculture Forest Service.
  • "Ostrya virginiana".  Missouri Botanical Garden Plant Finder. 
  • The International Union for Conservation of Nature and Natural Resources Red List of threatened species
  • The Plant List website
  • The Royal Botanic Gardens, Kew website and staff

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