Ash trees are members of the olive family. The species is distinguished by branches that grow opposite each other from the main trunk, compound leaves and diamond-shaped marks on the trunks of older trees. Most of the trees sold for landscaping will be male. Female trees spread large amounts of seeds with the result being a lawn full of seedlings the next spring. The wood of the ash tree is used to make baseball bats, tool handles and furniture.
White ash (Fraxinus americana) is the most common ash tree in North America. The tree tops out at a height of 40 to 60 feet, with a spread of about 40 feet. The compound leaves grow from 8 to 14 inches long and are composed of 5, 7 or 9 leaflets, dark green on the top and whitish on the underside, measuring from 3 to 5 inches long. The leaves turn red, yellow or purple in the fall. The tree will be either male or female, with small flowers growing in clusters and blooming in the spring. Female trees produce winged seeds in late summer. Plant white ash in full sun and moist, well-drained soil. The tree is hardy in USDA zones 4 to 9.
Green ash (Fraxinus pennsylvanica) is hardy in USDA zones 3 to 9 and likes full sun and moist, well-drained soil. The tree grows up to 50 feet tall and 30 feet wide with compound medium to dark green leaves up to 1 foot long, made up of 5, 7 or 9 leaflets. The leaves turn green and chartreuse or golden-yellow in September and October. Modern forms are seedless clones of male trees. Female trees have all but disappeared.
Common ash (Fraxinus excelsior) is native to Europe. The tree grows from 60 to 80 feet tall with a spread wider than the height. The compound leaves are medium-green, fuzzy, grow up to 1 foot long and are made up of 7 to 11 leaflets, each one 2 to 4 inches long. Green flowers bloom in the spring, and on female trees the flowers are followed by winged fruits containing one seed that measures 1 to 2 inches long. Plant common ash in full sun and moist, fertile soil.
Flowering ash (Fraxinus ornus) grows from 40 to 50 feet tall and about 25 to 35 feet wide. Dark green leaves are made up of 5 to 9 lance-shaped leaflets 3 inches long, and turn yellow in the fall. Fragrant white flowers bloom in the spring and female trees produce 1- to 2-inch-long winged seed pods. Plant flowering ash in full sun and moist, fertile soil.