Tree Spotlight: Fraxinus quadrangulata

Fraxinus quadrangulata

TRADE NAME: Blue ash

GENERAL DISTRIBUTION: Commonly found in the Midwest from Oklahoma to Michigan, as well as the Bluegrass region of Kentucky and the Nashville Basin region of Tennessee. Isolated populations exist in Alabama, Southern Ontario (Canada) and small sections of the Appalachian Mountains. Is typically found over calcareous substrates such as limestone, growing on limestone slopes and in moist valley soils.

WOOD VALUE: Is used to make flooring, baseball bats, furniture, tool handles, crates and barrels. Has also been traditionally used to build houses and can be harvested for firewood.

EMERALD ASH BORER CONSIDERATIONS: Blue ash appears to be least threatened in comparison to other North American ash by the infestation of the emerald ash borer. First detected in North America in 2002, this invasive beetle has since spread throughout much of this tree’s range. Approximately 60 to 70 percent of blue ash trees survive the emerald ash borer. (This is in comparison to other ash, such as black and green, where up to 99 percent fall victim to the emerald ash borer.)

FAMILY: Oleaceae

SEASONAL DEVELOPMENT: Flowering dates are March to April, while seed dispersal dates are September to October.

General Botanical Characteristics:

  • Grows up to 80 feet in height and 3 feet in diameter.
  • The crown is rounded and slender, while the bark is light brown to gray and fissured.
  • Is an excellent shade tree. It thrives in full sun on rich, moist, well-drained soils but is particularly tolerant of limestone soils and drought.
  • Its ability to survive in adverse conditions makes this a good tree for urban landscapes.
  • Blue ash doesn’t present the problem of weediness exhibited by green ash.
  • Bisexual flowers bloom as leaves emerge. The tiny, purple, petal-less flowers hang in loose panicles.
  • Fruit is a winged samara that is 1 to 2 inches long and hangs in clusters. Samaras fall from the tree over several weeks in autumn.
  • Has a very large, 7- to 14-inch leaf that’s divided into two rows of 2- to 5-inch, coarsely-toothed leaflets on either side of a central stem.
  • Leaves are dark green in summer and fade to pale yellow in autumn. The stem has small ridges that make it appear square.
  • Blue ash is unique among the ashes in the four-sidedness of its young twigs. It often has distinct lines, corkiness or wings at each of the four edges.

Management Considerations:

  • The lilac borer is the main pest problem. The lilac leaf miner, ash borer and fall webworm may be minor pests in this tree.
  • Leaf anthracnose and trunk canker are also diseases commonly found in the tree.
  • Seed litter from trees and surface roots (with age in compacted or shallow soils) are potential liabilities in urban areas.
  • Since blue ash is slower-growing than most other ashes, storm damage doesn’t occur as frequently, as its wood is more dense and stronger.

Sources: Oklahoma Biological Survey; Iowa State University Forestry Extension; University of Kentucky Dept. of Horticulture; Ohio Dept. of Natural Resources

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