Bulletin #2582, Native Trees and Shrubs for Maine Landscapes: Showy Mountain Ash (Sorbus decora)

Developed by Marjorie Peronto, Associate Extension Professor, University of Maine Cooperative Extension; and Reeser C. Manley, Assistant Professor of Horticulture, University of Maine.

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Go native!

This series of publications is the result of a five-year research project that evaluated the adaptability of a variety of native trees and shrubs to the stresses of urban and residential landscapes in Maine. Non-native invasive plants pose a serious threat to Maine’s biodiversity. Plants such as Japanese barberry, shrubby honeysuckle, and Asiatic bittersweet, originally introduced for their ornamental features, have escaped from our landscapes, colonizing natural areas and displacing native plants and animals. By landscaping with native plants, we can create vegetation corridors that link fragmented wild areas, providing food and shelter for the native wildlife that is an integral part of our ecosystem. Your landscape choices can have an impact on the environment that goes far beyond your property lines.

Description

Sorbus decora flowers — Photo by Reeser C. Manley

Form: a small tree with ascending branches that form low to the ground

Size: 20 to 35 feet high, up to three-fourths as wide

Ornamental characteristics:

broad, flat-topped terminal clusters of white flowers in late May or early June
heavy, drooping terminal clusters of bright scarlet red or orange berries from mid-August through October

Landscape Use

Sorbus decora fruit — Photo by Reeser C. Manley

Showy mountain ash can tolerate a wide range of soil moisture conditions, from poorly drained to well-drained, and thus can be found growing in swamps and bogs as well as on moist, rocky hillsides. Intolerant of shade, it frequents open hillsides and lake shores, growing with gray birch (Betula populifolia), paper birch (B. papyrifera), balsam fir (Abies balsamea), quaking aspen (Populus tremuloides), and red maple (Acer rubrum).

Because mountain ash is sensitive to many root-zone stresses, including drought, heat, and soil compaction, it should be mulched to maintain a cool, moist, acidic soil. The mulch should spread out beyond the trunk at least twice as far as the tree’s drip line (the edge of its canopy) in order to shelter the extensive root system.

This native species of mountain ash is equally as ornamental, both in flower and fruit, as the more commonly used European mountain ash (Sorbus aucuparia), and is far more resistant to disease.

Culture

Sorbus decora illustration — Drawing by Margery Read

Hardiness: USDA zone 2

Soil requirements: tolerates a wide variety of soils

Light requirements: full sun

Stress tolerances:

soil compaction — intolerant
pollution — intolerant
deicing salts — intolerant
urban heat islands — intolerant
drought — intolerant
seasonal flooding — tolerant

Insect and disease problems: frequent — fire blight, scab, cankers, borers, crown gall, pear leaf mite, mountain ash sawfly, and scale

Wildlife Value

The berries of mountain ash are eaten by waterfowl, and game birds such as ruffed grouse. Songbirds known to eat the berries include yellow-bellied flycatchers, cedar waxwings, thrushes, and grosbeaks. The fruits are also eaten by both small and large mammals, including humans.

Maintenance

Irrigation: During the establishment period, defined as one year after planting for each inch of trunk diameter at planting time, water your trees regularly during the growing season. Give the root zone of each tree 1 inch of water per week; in general, a tree’s root zone extends twice as wide as its canopy. After the establishment period, provide supplemental irrigation during periods of severe drought.

Fertilization: Landscape trees and shrubs should not be fertilized unless a soil test indicates a need. Correct soil pH, if necessary, by amending the backfill soil. No nitrogen fertilizer should be added at planting or during the first growing season.

To learn more about native woody plants

Visit the Eastern Maine Native Plant Arboretum at University of Maine Cooperative Extension’s Penobscot County office, 307 Maine Avenue in Bangor. Established in 2004, the arboretum displays 24 different native tree and shrub species that can be used in managed landscapes.

Reviewed by Cathy Neal, Extension professor, University of New Hampshire Cooperative Extension.
Photos by Reeser C. Manley.
Illustration by Margery Read, Extension Master Gardener.

This series of publications and the associated research were made possible in part by the Maine Forest Service’s Project Canopy.

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.

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