Quick answer: An ash tree has compound leaves made up of 5 to 9 leaflets, branches and buds that grow directly opposite each other, and bark with a diamond pattern on mature trunks. About 1 in 6 trees in Denver is an ash, so it is worth checking every tree on your property.
Emerald ash borer attacks only true ash trees, so identification is the first step. This guide gives a checklist you can use in any season. If you already know you have an ash, see ash tree removal and emerald ash borer help in Denver.
What does an ash tree look like?
- Compound leaves. Each leaf is a stem carrying 5 to 9 leaflets, with a single leaflet at the tip.
- Opposite branching. Branches, twigs and buds grow in pairs, directly across from each other.
- Diamond-patterned bark. Mature trunks have tight ridges that form a diamond or net pattern. Young bark is smooth.
- Paddle-shaped seeds. Seeds hang in clusters and look like small canoe paddles.
Opposite branching is the quickest test, because few common shade trees have it. In winter, look for the paired buds on the twigs.
Which trees are mistaken for ash?
| Tree | How it differs from ash |
|---|---|
| Boxelder | Opposite branching too, but only 3 to 5 leaflets and green twigs |
| Honeylocust | Alternate branching, many tiny leaflets, long seed pods |
| Black walnut | Alternate branching, 15 or more leaflets, round nuts |
| Elm | Simple single leaves with toothed edges |
| Mountain-ash | Not a true ash. Alternate branching and clusters of orange berries |
Which ash trees grow in Denver?
Green ash and white ash are the two planted most widely along Denver streets and in yards, including the purple-leaved fall varieties of white ash. Emerald ash borer attacks all of them. Denver has about 330,000 ash trees, according to the city’s Be A Smart Ash program.
What should you do if your tree is an ash?
- Note where it stands. A tree between the sidewalk and the street is in the public right-of-way, which changes the rules. See tree removal permits in Denver.
- Check its health. Look for dieback at the top, D-shaped holes and sprouts on the trunk. The full list is in our guide to emerald ash borer in Denver.
- Decide early. Treatment works on healthy trees, not failing ones. See should you treat or remove your ash tree?
What if you are still not sure?
Take a clear photo of a leaf, a twig showing the buds and the bark, and compare them with the photos on the Be A Smart Ash website. An arborist can confirm the species during an inspection. If it turns out not to be an ash, emerald ash borer is not a threat to it. If your ash stands by the street, see Denver’s free tree and ash replacement programs.
Ash tree identification FAQs
Is mountain-ash affected by emerald ash borer?
No. Mountain-ash is not a true ash, despite the name. Emerald ash borer attacks only true ash trees.
How can I identify an ash tree in winter?
Look at the twigs. Ash has buds and branches in opposite pairs, stout twigs and, on mature trunks, bark with a diamond pattern. Old seed clusters often hang on through winter.
How common are ash trees in Denver?
Very. About 1 in 6 trees in the City and County of Denver is an ash, which is roughly 330,000 trees.
