Cardinal Royal Mountain Ash
Sorbus aucuparia 'Cardinal Royal'
With so many possibilities in the Sorbus genus, it is difficult to decide which Mountain Ash to use. If a narrow upright form is needed, consider the Cardinal Royal Mountain Ash.
This tree is readily available and is easy to grow and transplant. 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 and 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. The bark is shiny dark brown and smooth until later age. On this variety, the limbs are well attached, but strongly ascending and appearing quite narrow, especially when young.
A minor downside is the heavy fruit that can pull the limbs down, disrupting the perfect upright form. In the nursery we have seen this as a short-term issue, remedied by a flock of birds that can quickly devour the fruit, with the limbs then returning upright. In our experience, 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.
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 diseases and insects that may become a problem, 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.