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Trees & Shrubs of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States

Green Ash Tree

Common Name
Green Ash (Swamp Ash, Water Ash)

 

Scientific Name
Fraxinus pennsylvanica Marshall

 

Plant Family
Olive (Oleaceae)

Garden Location
Woodland

 

Prime Season
Spring flowering

 

Tree Age Calculator

 

Green Ash is the most widespread native ash. It grows to a height of 60 to 70 feet, with a slim trunk and a dense rounded or irregular crown. The trunk is frequently poorly formed as the tree searches for bright light.

Bark is light gray to brown, furrowed into into interlacing corky ridges that form a diamond pattern. The inner bark is reddish.

New Twigs are green, becoming gray and may have fine hair initially, hairless later. New lateral buds appear on the top of the old leaf scars which are semi-circular with the top part more flat.

Leaves are opposite and pinnately compound, 6 to 10 inches long, with 5 to 9 (usually 7) shiny green leaflets in pairs plus the terminal leaflet; these are ovate to lance-shaped in form, whose margins are either smooth or coarsely saw-toothed. Each leaflet has a short stalk and the leaf has a much longer stalk. The underside of the leaflet is paler and may be slightly hairy. Fall color is yellow.

Flowers: The tree is dioecious, that is the male and female flowers are on different plants. Both appear before the leaves in small clusters on the prior years wood. They are light green to greenish-purplish, only 1/8 inch long, with a small tubular calyx and without corollas. Male flowers have two stamens with long anthers and the male flowers turn brown after release of pollen. The female flowers have a pistil and a single style. The male clusters are tightly composed whereas the female clusters start that way but then greatly expand to form a loose panicle containing 200 to 300 flowers. Flowers are cross pollinated by wind. Some studies indicate that male trees flower every year but female trees flower every 2 to 5 years.

Seed: Female flowers mature to a single narrow winged samara, 1-1/4 to 2-1/4 inches long, that is flattened in appearance due to the thin seed cavity for the small seed, and the wing extends nearly to the base of the samara. These turn straw-yellow, 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 20 to 30 feet in height before they bear seed.

 

Habitat: In its native habitat Green Ash is found in moist riparian soils. It adapts to a wide variety of soils and moisture conditions. Seedlings do best in moist shady soil but for mature growth they must then have full sun. The root system is extensive but shallow. The tree will re-sprout easily and quickly from stumps and cuts. The Emerald Ash Borer is a serious pest of this tree. The twigs and small branches are somewhat brittle and the tree is quite good at self-pruning in a windstorm.

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, pennsylvanica means 'of Pennsylvania' where the tree was first classified. The author name for the plant classification - ‘Marshall’ refers to Humphry Marshall (1722-1801), American Botanist, who published in 1785 - Arboretum Americanum: The American Grove, an Alphabetical Catalogue of Forest Trees and Shrubs, Natives of the American United States.

Comparisons: Green Ash is easily confused with Black Ash (F. nigra) and White Ash (F. americana). Comparison of the samaras is the best method of identification.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

Green Ash tree Green Ash leaf Green Ash leaf

Above: 1st photo - Green Ash has a slender trunk with an irregular to rounded crown. 2nd & 3rd photos - Leaves are pinnately compound with 5 to 9 (usually 7) shiny green leaflets, each on a short stalk.

Below: 1st & 2nd Photos - Bark is light gray to brown, furrowed into into interlacing corky ridges that form a diamond pattern. 3rd photo - Leaves can have some fine whitish hair on the underside.

Green Ash bark Green ash bark leaf underside

Below: 1st photo - Buds appear at the top of old semi-circular leaf scars. New twigs are green, becoming gray and may have fine hair initially, hairless later. 2nd & 3rd photos are 2nd year twigs in the spring.

Green ash twig Green Ash twig Green Ash twig

Flower Development

Below: 1st photo - A cluster of male flowers. 2nd photo - Female flowers developing on the prior year's twig. 3rd photo - The female flower cluster elongates as the leaves develop.

Green Ash male flowers Green Ash Female Flowers Green Ash female flowers

Below: 1st photo - Male flowers developing. 2nd photo - Detail of the female flowers after the cluster elongates and samaras start to form.

Male flowers Green Ash female flowers

Below: Green Ash Seeds: The seed is a narrow winged samara, 1-1/4 to 2-1/4 inches long, that is flattened in appearance due to the thin seed cavity for the small seed, and the wing of the samara extends nearly, but not completely, to the base of the samara. Mature fall color is yellow (3rd photo). The tip of the wing is rounded and sometimes with a slight notch.

Green ash seeds Green Ash seeds Green Ash Fall seed

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.

seed comparison

Notes:

Notes: Green Ash is not indigenous to the Garden. Eloise Butler first planted it in May 1909 with plants from the Park Board Nursery. It is the most widespread native ash in North America, ranging from the Rocky Mountains eastward to the coast although some researchers believe that some plants in the Rocky Mountains are escaped from cultivation. Within Minnesota there are only 7 widely scattered counties where Green Ash has not been found. Only three species of ash are native to Minnesota with known populations - Green Ash plus Black Ash (F. nigra) and White Ash (F. americana).

Uses: Green Ash has been extensively used as a landscape tree, particularly clones that do not produce seed. It is also used for shelter-belts and for cover on strip mine reclamations. It is a moderate source of food for wildlife.

References and site links

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.

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