White Ash is a large long-lived native deciduous tree growing to 80 feet in height and 2 feet in diameter with a straight trunk and a dense conical or rounded crown.
The bark is ashy-gray to dark gray with diamond shaped furrows with corky scaly ridges on older trunks. Older trunks are usually free of lower branches.
Twigs are stout, olive green initially turning gray, hairless with leaf scars that are round at the bottom and notched at the top. The brown lateral buds rise from this notch. The terminal bud is large, scaled and flanked by smaller lateral buds.
Leaves are opposite and pinnately compound, 8 to 12 inches long, with 7 (sometimes 5 to 9) dark green paired leaflets (exc. the terminal leaflet which is single) that are ovate to elliptical, whose margins are either almost smooth or finely saw-toothed. Each leaflet is stalked and the leaf has a much longer stalk. The underside of the leaflet is paler, almost whitish, hence an allusion to the common name. Fall color is yellow to purplish.
Flowers: The tree is dioecious, that is the male and female flowers are on different plants. Both appear before the leaves in small clusters. They are only 1/8 inch long, with a small tubular calyx and without corollas and form near the branch tips. Male flowers are yellow-green to purplish, on the prior year's wood and have two stamens with long anthers. The female flowers have a pistil and a single style and form also on the prior years wood. Both male and female flower clusters are tightly composed when formed, then the male flowers expand to expose the stamens and the female clusters greatly expand to the shape of a loose panicle. Flowers are cross pollinated by wind but male flowers shed pollen up to 10 days prior to the female flowers being receptive, thus multiple trees are needed for good seed production.
Seed: Female flowers mature to a single narrow winged samara, 1 to 2 inches long, that is rounded in appearance toward the base with a rounded seed cavity for the small seed, and the wing of the samara does not extend beyond the rounded seed cavity of the samara. These are greenish initially and turn brown, mature in autumn and disperse by wind in fall and winter. They do not germinate until the following spring as a cold stratification period is needed. Trees usually need to reach 3 to 4 inches in diameter before they bear any significant seed.
Habitat: White Ash grows best on well-drained moist soil with full sun. The root system is shallow and spreading. It can re-sprout from the root crown. The color of the wood is white, thus the common name.
Names: The genus, Fraxinus, is the old Latin name for this genus meaning 'spear'. Ash wood, being tough and elastic, was originally used for spears and bows in the old world. The species, americana means 'of America' as the tree is a new world species. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: White Ash is easily confused with Black Ash (F. nigra) and Green Ash (F. pennsylvanica). Comparison of the samaras is the best method of identification, although the leaflets of White Ash are more whitened on the underside and the leaf scars have a definite notch at the top side where the new buds arise. Black Ash leaflets do not have stalks.
Above: 1st photo - A white ash of mature size. 2nd photo - Fall color of the white ash. 3rd photo - Bark is ashy-gray to dark gray with diamond shaped furrows with corky scaly ridges on older trunks
Below: 1st photo - Spring twig showing prior year growth - olive green color. Terminal buds are flanked by lateral buds. 2nd photo - This spring twig of the prior year's growth shows the semi-circular leaf scars that have a notch at the top where the new lateral buds emerge. 3rd photo - The terminal leaflet of the compound leaf. Each leaflet has a short stalk. Margins may be entire or may have a few shallow teeth near the tip.
Below: The compound leaf 4 to 8 paired leaflets plus the terminal leaflet.
Below: Flowers of White ash form at the tips of old growth in a tightly composed cluster. Each flower is only 1/8 inch long. 2nd photo - Male flowers before elongation.
Below: 1st photo - Female flowers just beginning to expand. 2nd photo - Fully extended female flowers.
Below: Fully extended male flowers.
Below: 1st photo - Mature samaras of White Ash have a rounded seed cavity near the base and the wing does not extend beyond the rounded seed cavity of the samara.
Comparison: Ash samaras are a key distinguishing characteristic of the three common species. Position of the wing vs the seed and thickness of the seed are important. Overall length and width are variable between trees within a species and not useful.
F. nigra has a flatten broad seed with the wing extending to the base of the seed cavity. F. americana has a noticeably thick seed, rounded, and the wing does not extend beyond the seed cavity. F. pennsylvanica has a smaller seed with the wing extending into the seed cavity, but not all the way to the base.
Notes: White Ash is believed to be indigenous to the Garden as Eloise Butler catalogued it on April 29, 1907. She also planted it in May 1909 with plants obtained from the Park Board Nursery, located at the time, at Glenwood Lake [now named Wirth Lake]. In North America it is found in the Eastern half of the U.S., reaching westward to Minnesota on the north and the central plains further south. In Canada it is found in Ontario, P E Island and Quebec. Within Minnesota it is quite restricted with native populations only known from 14 counties on the eastern side of the state with Mille Lacs and Pine county on the north and Fillmore and Houston on the south. Only three species of ash with known populations are native to Minnesota, White Ash plus Black Ash (F. nigra) and Green Ash (F. pennsylvanica).
Uses: White Ash wood is hard and strong, second only to hickory for use in tool handles, baseball bats and other sports equipment. The wood is used in furniture, boats and other areas where a strong dense wood is desired. It is useful as an ornamental if grown in the open, but it is a slow-grower and has more pest problems than the Green Ash (ash yellows being the most serious).
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"