Fast-Growing Rowan Tree Tolerates Air Pollution

The misnomer occurs mostly in North America. This fast-growing, hardy tree (Sorbus aucuparia) is a member of the Rose (Rosaceae) family. It is a familiar wild tree in the British Isles. In Newfoundland-Labrador and Nova Scotia, Canada, it is commonly referred to as the Dogberry Tree. The name Mountain Ash has applied also to the Sorbus americana.

Air Pollution Tolerant Tree in the Landscape

Frequently grown as an ornamental, the Rowan is also well suited to planting on residential streets. In urban areas, it is often planted as a privacy or windscreen, or an excellent landscape specimen. It has been successfully grown where air pollution and poor drainage prevail.

The Rowan is an upright oval tree that grows to about thirty feet. Of slender form with branches that spread upward, it offers a pleasant open canopy. At maturity, the tree develops a rounder shape. There are also some weeping varieties. Occasionally, multi-stemmed forms develop from basal roots.

Foliage, Fragrant Flowers, and Fruit of Rowan Tree

The Rowan’s dark green leaves measure up to fifteen inches in length. Each leaf comprises nine to fifteen serrated leaflets in matched pairs (pinnately compound), with a single leaflet at the end. Deciduous, they turn yellow or reddish in the fall. Rowan leaves are not palatable to plant-eating insects.

The individual five-petalled flowers of the Rowan are less than one-quarter inch in diameter. Creamy white, they grow in dense clusters of more than two hundred flowers. The clusters measure up to six inches in diameter. Pollinating insects are attracted to their strong, sweet scent.

The fruit of the Rowan is a brightly-colored berry in scarlet or dark yellow. Each berry contains an average of four seeds which are dispersed by birds’ droppings. The showy clusters often hold on until the winter birds find them. Caution should be taken with the raw berries that are said to contain a cancer-causing compound. That element is neutralized when the berries are cooked.

Berries Eaten by Cedar Waxwings during Winter

Observers recorded seeing a very large flock of cedar waxwings at the height of winter. They converged on a large Rowan tree and cleaned off all of the berries. In extremely harsh climates, the fruits may occur only every few years.

The Rowan requires rich, well-drained soil. Saplings are shade tolerant, but for full effect in the landscape, the tree should be planted in full sun. If grown in shade, the Rowan will develop a poor shape. It requires no pruning but does need additional watering during droughts.

The Rowan (European Mountain Ash) shown with ripening berries in the attached photographs is about seven years old. It bore a few fruit clusters in its fourth year and produced more each year since then.