Cardinal Royal Mountain Ash

Sorbus aucuparia ‘Cardinal Royal’

Sorbus, also known as the Mountain Ash or Whitebeam are a genus with numerous and wide ranging qualities. Checking the literature on Sorbus, the possibilities seem endless, so it is not surprising the difficulty in deciding which Mountain Ash to use. If a narrow upright form is needed, the Cardinal Royal Mountain Ash, Sorbus aucuparia ‘Cardinal Royal’ is a good one to consider.

I am surprised this particular tree is not more popular. It is fast and easy to grow, and readily available. If you will tolerate, or should I say enjoy some very beautiful fruit, the Cardinal Royal is an excellent street and landscape tree. Like the majority of Sorbus, the leaves are alternate, pinnately compound, 5-9” long, with 9-19 leaflets. Individually they are 1-2.5” long, oblong to oblong lanceolate, serrate along the edge, pubescent beneath, at least when young, with leaflet base asymmetric. ‘Cardinal Royal’ is a vigorous grower with symmetrical, upright, narrow-oval form, leaves dark green above, silvery beneath, showy white flowers in spring and with brilliant red fruit in August and September. The ultimate mature size is about 35’ tall by 20’ wide, probably larger in perfect locations. The bark is shiny dark brown and smooth until later age. On this variety, the limbs are well attached but strongly ascending, appearing quite narrow, especially when young.

The small downside to this tree is that the fruit can be so heavy that it can pull the limbs down, disrupting the perfect upright form for a short while. In the nursery we have seen this as a short-term issue, quickly remedied by a flock of birds that can quickly devour the fruit, with the limbs returning upright.

In the nursery we have found them to transplant easily. We have also observed a relatively small, non-aggressive and limited root system, thus I would not anticipate them to cause any infrastructure damage. They appear to thrive on relatively limited sites also.

The literature warns that stress may predispose them to canker and borer and we have seen them struggle on poor, compacted soils. There are a number of disease and insects that may become a problem on Sorbus but primarily this occurs when the tree is weak or in a poor growing location. Like most trees, the best line of defense is to grow a vigorous healthy tree in the first place (Dirr, 1998).

Email me if you have any comment on this variety or other species used in the landscape so I can pass it on.