City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: http://read.dmtmag.com/i/1049849
Tree of Merit: Oakleaf Mountainash (Sorbus x thuringiaca) Hybrids and cultivars have been developed f rom many species of Sorbus, and oakleaf mountainash is most commonly classif ied as Sorbus x thuringi- aca, a hybrid cross bet ween S. aucuparia and S. aria. Oakleaf mountainash leaves are dark green with sil- ver y undersides and are deeply lobed, resembling those of an oak. Mountainash is a member of the Rose family and is not related to true ash (Fraxinus). Oakleaf mountainash is native across Europe and has been introduced in the U.S. and Canada as an orna- mental selection. It is adapted for a shor t growing season, requires cold temperatures for bud break , and has a USDA Hardiness Rating of Zone 3. It pre- fers full sun but will tolerate shade. If drought stress is not a factor, oakleaf mountainash withstands the summer heat without dif f icult y. It is quite tolerant of urban conditions and adapts readily to a variet y of soil t ypes but will not sur vive if planted in a water- logged site. Oakleaf mountainash t ypically grows to a height of about 30 feet ( 9 m) and is considered a shor t-lived tree, not usually exceeding 100 years. Hermaphroditic clusters of small, white f lowers are pro- duced each spring, followed by berr y-like orange-red f ruits that light up the landscape with splashes of bright color. In fall, its leather y, compound leaves turn f rom dark green to the most brilliant shades of orange or red, another at tribute of exceptional ornamental qualit y. Oakleaf mountainash maintains a tidy, upright oval shape, more so than European mountainash (S. aucuparia), and has numerous ascending branches. Characteristic of its genus, branch angles are narrow with included bark , leading to occasional breakage if loaded f rom wind or snow. It is possibly more resistant than other varieties to f ireblight, a bacterial disease af fecting members of the Rose family, and is not susceptible to any serious insect problems. Oakleaf mountainash is a hardy, reli- able ornamental with excellent fall color and an impres- sive f ruit display. For those in nor thern climates, this tree adds aesthetic value to almost any landscape. —Jennifer Jolliff, ISA Certified Arborist, Municipal Specialist, City of Bozeman, Montana Forestry Division by Jennifer Jolliff, Arborist, Bozeman, Montana Below: Oakleaf mountainash fruit (left) and bark with lenticils (right). Photos by Ethan Dropkin 38