Mountain Ash: (Sorbus spp)
These medium sized trees have a multi-season appeal but they must be in well drained soil or they will have health issues. That said, in the right location they are a great tree.
Two varieties are of a scale and hardiness suitable to the Calgary climate:
Russian Mountain Ash (Sorbus aucuparia ‘Rossica’) has a somewhat columnar form.
Showy Mountain Ash (Sorbus decora) has a more rounded form and more showy flowers.
Size & Characteristics: Russian Mountain Ash matures at 4m wide (13’) by 8m (26’) tall. It has compound leaves lending it a softer look than some trees. Spring brings large clusters of showy flowers that by fall have become clusters of orange fruit. Birds (wax wings, robins etc.) love them. The bark is a reddish-brown.
Showy Mountain Ash matures at 4-5m (13-16’) by 5-6m (16-20’) so more rounded form and has a more showy spring flower than the Russian variety. The fruit is red.
Pests and Diseases: If they aren’t happy Mountain Ash will contract a variety of nasty diseases but in the right location they will usually stay healthy. Young trees must have the bark protected against sunscald in the winter months.
There are other varieties of Mountain Ash that are rated to grow larger but in general struggle in the Calgary climate. The Pyramidal Mountain Ash (Sorbus aucuparia ‘Fastigata’) with a rated width of 2m (6.5’) is worthy of consideration but I can not recommend it at this time due to lack of personal experience with it. (It should be hardy though based on it’s parentage and useful in a smaller garden)
© Clayton Ditzler