The red female flowers and the yellowish-green male catkins , amidst new foliage .
Mature foliage during the summer months .
It even catches the eye of airplane passengers flying overhead . Plant explorer Dan Hinkley can attest to that !
“ I once flew so often ,” says Dan , “ that when we landed in Seattle from the north and I had a window seat , I would take the time to look at the Arboretum and — as a hallmark — would first find Quercus robur ‘ Concordia ’. It was always a game , but I was quite successful in finding it during spring and summer .”
The soft-yellow color of the leaves is at its brightest early in the season . By late summer , the leaves mature to a light or medium green . The fall color is somewhat unremarkable ; in his “ North American Landscape Trees ,” Arthur Lee Jacobson describes it as “ paper-bag brown .”
The tree is a cultivar of the common oak , Quercus robur , which is native to much of Europe . In “ Trees and Shrubs Hardy in the British Isles ,” William Jackson Bean says ‘ Concordia ’ was first discovered in 1843 in Van Geert ’ s nursery in Ghent , Belgium . It was introduced to cultivation in North American around 1888 , but Arthur Lee says the cultivar is still very rare here .
The golden oak flowers in spring , typically in April , when the leaves are first emerging . They consist of tiny , red female flowers and yellowish-green male catkins . Acorns mature in fall , but the cultivar ‘ Concordia ’ does not
come true from seed and has to be propagated from cuttings .
Golden oaks are low-maintenance trees , but you need to be patient with their very slow growth rate . We have not observed leaf scorch late in the season . We do monitor in May for oak leaf phylloxera ( Phylloxera glabra ), an aphid-like insect that causes leaf spotting and , if serious , necrosis followed by leaf drop . In the past , we have treated our most susceptible oaks in the collection using horticultural oil during the dormant season , but with mixed results . We are hoping for better results by treating crawlers when they emerge following leaf expansion in spring .
Our golden oak is the only one to survive of three plants that we acquired in 1947 from Layritz Nursery , Victoria , British Columbia . It was planted out in 1951 along Azalea Way , just north of lower Woodland Garden pond . It is now 74 years old and going strong ! At about 43 feet tall and wide , it is well over the referenced size for ‘ Concordia ’ ( 25 to 30 feet ). May it continue to serve as a shining beacon of hope in the coming days , as we all work together to defeat the scourge of the coronavirus pandemic ! m
Adapted from a post that first appeared on the UW Botanic Gardens blog , botanicgardens . uw . edu / about / blog .
David Zuckerman is the manager of Horticulture at UW Botanic Gardens .
4 v Washington Park Arboretum Bulletin