Plant of the Month

 

Plant of the Month Archive

Well-Mannered Wisterias!

Some plants instantly instill fear in both gardeners and non-gardeners alike.  Bamboo is certainly one of the leaders in this category, only to be closely followed by Wisteria!  The challenge these plants display is their ability to escape cultivation when maintenance levels become less than optimal.  As with Bamboo, not all Wisteria species are equally aggressive.  In fact, Wisteria frutescens and Wisteria macrostachya are not only well-mannered, but are native to North America and should be included more frequently in NJ Gardens!
Wisteria is a member of the Pea Family or Fabaceae, containing between 5 and 8 species that are distributed throughout Eastern North America and Eastern Asia.  The genus name was first penned in 1818 by the English botanist and zoologist Thomas Nuttall (1786-1859) within his publication, The Genera of North American Plants.  Nuttall claimed that he named the genus in honor of Dr. Caspar Wistar (1761–1818), the late professor of Anatomy at the University of Pennsylvania.  Of course, the spelling does not quite match and when Nuttall was questioned, he simply claimed that the misspelling better matched how the Doctors name was pronounced.  However, Nuttall also had a friend named Charles Wister Sr. who mentioned that the plant was named after his grandfather, John Wister.  The truth be told, we shall probably never know! 


Nuttall’s version of the genus name was also not the first attempt to name this group of plants, nor was the more showy Asian species, with their 36” long floral racemes the first to be described!  In 1724, the British naturalist and aWisteriartist, John Catesby (1682-1749) introduced to Britain a plant he called Carolina Kidney Bean, since the seeds were spotted and as large as kidney beans.  Nearly 30 years later, the Swedish Botanist and Physician, Carl Linnaeus (1707-1778) described and named this plant as Glycine frutescens.  The species epithet is from the Latin Frutex for woody.  The genus Glycine includes to this day Soybeans, so it only makes sense that Linnaeus would name this plant as the woody relative!  In 1823, the French clergyman and botanist, Jean Louis Marie Poiret (1755-1834) decided that this plant and the plant that Nuttall called Wisteria speciosa were in fact one in the same and he renamed it Wisteria frutescens!  It was not until 1906 that the name was officially accepted.


Fortunately, Wisteria frutescens was well worth the time and effort to name, as it is a great garden plant. Commonly called the American Wisteria, it is native from Texas to Iowa and east to Massachusetts and Florida.  The pea-like flowers typically appear tightly compressed in numbers of 30-65 along a 5-7” long central stem – a flower structure that is called a raceme.  Similar to the Chinese Wisteria, Wisteria sinensis, the vinesWisteria climb in a counterclockwise direction up a support when viewed from above.  Unlike the Asian cousins, the plants grow to a more manageable size of 20-25’ in height and flower freely at an early age.  The flowers are faintly scented and vary in color, but blue-violet is typical, although white and purple selections are ample.  Currently, the most common cultivar is ‘Amethyst Falls’ (pictured above on the right), which was found in Oconee County, South Carolina.  True to the name, the flower are amethyst purple and hang attractively from the plant, while the cultivar ‘Nivea’ (pictured at right) sports attractive white flowers.


Wisteria macrWisteriaostachys or Kentucky Wisteria is native from Texas to Illinois, including Kentucky and was originally considered a variety of Wisteria frutescens, before gaining species status.  The plant was first described as a variety in 1838 by the famed botanical team of Asa Gray (1810-1888) and his mentor and friend John Torrey (1796-1873).  Evidently, Nuttall shifted it to species status in an unpublished manuscript.  The epithet means ‘long spikes’ and refers to the longer, 8-10” flower racemes that contain clusters of 70-80 flowers (pictured at left).  Similar to its cousin, the lightly scented flowers are blue to pale violet and appear on spurs along the counterclockwise growing vines that grow to 20-25’ in height.  ‘Blue Moon’ is a selection with attractive, light blue flowers (pictured below).


Both species are native to moist woodlands, stream banks and ponds sides in the wild, but they are perfectly at home in average garden soil.  Since they are members of the Fabaceae, they fix their own nitrogen, allowing them to tolerate lower fertility soils.  In fact, the addition of nitrogen often produces an excess of vegetative growth and reduced flowering.  Unlike their Asian counterparts, they bloom freely from an earlWisteriay age, with the flowers opening concurrently with the foliage, although the foliage does not impact the floral display in the least.  Flowers also appear sporadically throughout the summer.  The vines will grow luxuriantly in the shade, but the best flowering is delivered in full sun locations.  Once the vines reach the desired height, a light pruning in mid-summer, following by a repeated light trim in late winter is beneficial.  The flowers appear from short spurs on wood that is typically 2 years old or older.  Obviously, care should be taken not to remove the spurs!  The foliage also serves as a host for the larva of Silver-Spotted Skipper which is native to much of North America and Long Tail Skipper found throughout the south. 
Aside from removing the occasional seedling from the base of the plant, some light pruning and a little training, both of these Wisteria species provide a charming and well-mannered addition to arbors or other garden supports, erasing any fears that there is a potential garden monster in our midst!   

Bruce Crawford
Rutgers Gardens