Blue Ash

Size, growth and what to expect

Blue ash is a long-lived tree, 150 to 200 years and sometimes 300. One tree in central Kentucky was estimated from core samples to be 405 years old. The oldest tree dated by its rings reached 249. Only a tiny share of trees is ever dated this way, so older ones may exist. Our growth estimator models it as a medium tree at roughly a foot and a half a year, between Iowa State's moderate to fast and Kentucky's moderately slow. A mature tree stands 50 to 70 feet tall with a trunk 18 to 40 inches through, and the crown spreads 25 to 35 feet.

The first seed comes at about 25 years, with a heavy crop every 3 to 4 years. The winged seeds run 1 to 1½ inches long and feed birds and small mammals. Early settlers soaked the inner bark to draw a blue dye for yarn, which gave the tree its name.

It grows wild on rocky bluffs from southern Ontario and Michigan west to Wisconsin and Iowa, and south to West Virginia, Alabama and Oklahoma. It is the North American ash least affected by the emerald ash borer, and it has stood where white and green ash have died.

How to grow Blue Ash

Blue ash wants full sun and dry to average soil, and unlike most trees it prefers thin, alkaline ground over limestone. It grows an open, rounded crown, so set it 35 feet from the house and out from under wires. Set trees about 50 feet apart.

Plant in the dormant season. Saplings arrive bare-root or potted. Make the hole twice as wide as the root mass and no deeper, keep the root flare visible at grade, and return the soil you dug without amendments. Mulch a ring clear of the trunk. Sow seed outdoors in fall and leave the bed a full winter, or longer, before seedlings show.

Water through the first summer when rain fails. Rabbits and voles chew the thin young bark, so guard the lower stem, and tube or cage against deer until the leader clears six feet. Remove a competing leader in winter and leave the rest alone.

Unlike most ashes, blue ash usually carries male and female parts in each flower, and few trees are only male or female. The wind carries the pollen. Emerald ash borer attacks blue ash like any other ash. What sets it apart is how many mature trees survive and recover, though young trees still need watching. It handles drought, heat and high pH better than white or green ash. Fall color is a clear yellow.