Fraxinus quadrangulata aka Blue Ash

Fraxinus quadrangulata, or blue ash, belongs to the olive family. This deciduous tree grows across central and eastern North America. Its range includes southern Ontario, Michigan, Arkansas, and Tennessee. It grows on dry, rocky slopes and limestone sites. In Missouri, these include Ozark woods, glades, and bluffs. Its name comes from blue dye made from inner bark.

Garden trees reach 50–75 feet [15.2–22.9 metres] tall. Some sources give a narrower range of 50–60 feet [15.2–18.3 metres]. Crowns spread about 50–60 feet [15.2–18.3 metres] across. One source records widths reaching 70 feet [21.3 metres]. The crown may be oval, pyramidal, or rounded and uneven. Growth is slow to moderate, depending on the source. Gray or brown bark develops grooves and uneven ridges. Young twigs have four sides with raised, corky edges. The buds range from gray to reddish brown.

Leaves grow in pairs and have a pinnate form. Each leaf bears five to eleven leaflets, often seven to nine. These have pointed tips, toothed edges, and short stalks. Their upper sides are dark green and may look glossy. Fine hairs grow beneath, near the main veins. The leaves turn pale yellow before they fall. Small purple flowers appear in spring, often during April and May. They lack petals and add little garden color. Winged fruits, called samaras, hang in clusters. They turn brown or tan as they ripen in fall.

Blue ash grows best in full sun and well-drained soil. It prefers moist, fertile loam but also suits dry sites. It accepts clay, sand, and a wide soil pH range. It tolerates drought and alkaline ground, including limestone soils. North Carolina State notes that it dislikes flooded ground. Sources place it in USDA hardiness zones 4–7. Its size suits large lawns, parks, and street plantings. Birds and mammals eat its seeds. Moth and butterfly larvae feed on its leaves. Tadpoles eat fallen leaves, and the tree offers wildlife cover.

Emerald ash borer poses a serious threat to this tree. Blue ash may suffer less than other North American ashes. Other problems include borers, scales, leaf miners, and ash dieback. Mites can cause flower galls, and seeds may yield unwanted seedlings. Some sources report slow establishment and difficult propagation. Its hard, heavy wood serves for floors and indoor finishes. Plants For A Future lists no known food or medicinal uses. That source also reports no known hazards.