By Bev Johnson

Master Gardener

If you are looking for a smallish tree that is attractive all year, check out some of the Mountain Ash trees. In the spring they are covered with lacy, umbels of white. The leaves are long, medium green and lacy. A mature tree will be oval or a broad pyramidal shape depending on the cultivar. 

In the fall the flowers give way to pendant clusters of reddish orange berries that fill the trees with robins and Cedar Waxwings. If they don’t strip the tree of berries in the fall, the few that are left ferment. This leads to drunken robins in the spring.  

Fall color is shades of yellow, orange red or purple depending on the cultivar. She may be cause of blue air at times as she likes to keep hold of her leaves until all the other trees in your yard are totally bare.  she prefers cool dry summers. We sure hit the dry bit, but Bunkey’s tree did quite well this year although it didn’t have as many flowers or berries as usual.

Mountain Ash is of the genus Sorbus. It is known for producing multiple hybrids and cultivars. It is a bit of a light skirt genus as it will readily breed with plants of different genera like Aronia, Cotoneaster, and Pryus.  This has led to some unique intergeneric hybrids with names like Sorbaranoria and Sorbocotoneaster

 The European Mountain ash, Sorbus aucuparia, is called a Rowan tree. This is the one you have if she is an older tree. She has naturalized across the northern U.S. It spreads by seeds as they go, intact, right through a bird getting fertilized on the way out. It is so hardy that Washington and Alaska deem her invasive and a few others have her on a watch list. Not here, however, zone 4 tree.

Mountain Ashes are not a city tree. Stress from pollution makes them more susceptible to pests and disease. They are northern trees as most won’t grow south of zone 6. Fire blight and borers make them unpopular to landscapers.

Korean Mountain ash, Sorbus amifolia, is the most borer resistant. She is the most fast growing and has a densely branched form with a 20 to 25 foot spread and a height of 40 to 50 feet. It turns a golden orange in the fall. Cultivar Redbird has bright pink, orange or scarlet berries that persist into the winter.  A great food source for the birds. She grows in zone 3 to 7.

Our native American Ash, S. americana, is a smaller girl only 15 to 30 feet high and wide. She is usually a multiple stemmed understory tree or tall shrub.  She has bright red-orange berries and a yellow fall color.  Zones 3 to 6.

Another native is the Showey Mountain ash. Another understory tree/ shrub growing 20 to 30 feet tall and 15 to 20 feet wide. This girl unlike the others, can tolerate wet feet. Sorbus Decora is found mostly in the Northeast. She has heavy clusters of shiny red fruits.  The fruits are so heavy they bend the branches down when they are ripe. She blooms later than her cousins, sometimes into June or July in the far north zones. She has red to yellow fall color, and grows in zone 2 to 6.

More interesting cultivars next week.

It’s a good time to plant trees and shrubs as we should have the 6 weeks of hard frost free, they need to get well established so, go dig that hole.