Majestic trees for Fall Colour
aCommon Name: ash trees
Botanical Name: Fraxinus spp.
Form: upright tree with mostly round canopies
Species: numerous including cultivars
Plant Type: deciduous tree, subtropical species are evergreen
Mature Size: depends on the species
Growth: 2 feet per year, but grow slower as they mature and if crowded
Origin: depends on species
Hardiness Zone: depends on species
Foliage: opposite green leaves are pinnately compound
Flowers: some are dioecious (male and female flowers are on separate plants)
Fruit: samaras, keys, (seeds have wings)
Stems: flattened at tip
Exposure: full sun
Soil: well-drained organic rich soil, but is soil tolerant
Uses: shade tree, street tree, birds
Propagation: seeds, cuttings
Pruning: late winter, but often it is not necessary
Problems: emerald ash borer is a serious pest that will kill the tree in 3 to 5 years, ash borers, scale, anthracnose
Ash trees (not to be confused with mountain ash (Sorbus), are coveted for their majestic beauty, brilliant autumn colours and for being effective shade trees. Their popularity is waning however, due to their arch nemeses, the emerald ash borer (Agrilus planipennis). It is a killer - if left untreated. Because of this destructive pest, many communities warn against planting ash trees. However, there are solutions to this pest. Tree service experts use an approved insecticide, imidacloprid as a soil drench or inject it into healthy trees. In British Columbia, this insect is not a serious threat, unlike the U.K. and Europe. The green ash (Fraxinus pennsylvanica) and the narrow-leaf ash (F. angustifolia) have shown some borer resistance.
White Ash: Fraxinus americana, native to Eastern North America, USDA Zones 3 to 9, 60’ – 80’ tall and wide. It is one of the largest ashes. Prefers moist, rich well-drained loams but tolerant to slightly alkaline soils. Moderate tolerance to drought. Locate away from strong winds as their branches are brittle. Immature trees are pyramidal and mature to a rounded crown. Purplish non-showy flowers in April to May. Clusters of drooping seeds up to 2 inches long have wings (samaras, keys) on female trees. Leaves are pinnate compound with 7 oval or oblong leaflets 3-5” long. Foliage is dark green above and whitish green on the undersides. In autumn, leaves turn yellow and purple. Diamond shaped ridges appear on the grey mature trunks. White ash is used for lumber, furniture and sports equipment including the Louisville Slugger baseball bats.
European Ash: Fraxinus excelsior, native to Europe and western Asia, USDA Zones 5 to 7, 50 to 60’ x 40 to 50’. Prefers well-drained rich loam in full sun. Prefers cool summers and dislikes hot and dry climates. An oval crown with 8 to 14 inch long pinnately compound leaves with 7 to 13 leaflets. Leaflet margins are elliptical and coarsely serrated. Yellow autumnal colour. No significant flowers. Bark is smooth and grey on immature trees then becomes deeply ridged as trees mature. Black buds are a distinguishing feature.
Green Ash: Fraxinus pennsylvanica, native to North America, USDA 3 to 9, 50-70’ x 35-50’. Prefers well-drained, organic rich moist soils in full sun. Immature trees are pyramidal and mature to roundish crown. Similar to white ash but the leaves are serrated at the ends, and are green underneath and petioles (leaf stems) are winged. Leaves turn bright yellow in autumn. Flowers appear after the foliage in spring. Purple flowers in spring followed by profuse clusters of weeping samaras up to 2 inches long. Seeds are viable resulting in seedlings. Bark is greyish brown that matures to diamond-shaped ridges. Wood is used for lumber, furniture and sports equipment. Green ash have shown some resistance to emerald ash borer.
Narrow-leafed Ash: Fraxinus angustifolia, native to central & southern Europe, northwest Africa, southwest Asia, USDA Zones 5 to 8. Grows quickly, 80’x 30 – 50’. Prefers acidic soils. Smooth grey bark becomes deeply ridged with age. Foliage comprised of green, narrow, lance-shaped, 7 to 13 leaflets that turn yellow in autumn, pale brown buds rather than black ones. It has a slightly greater resistance to the emerald ash borer.