Ash trees: Modesto, Raywood and green ash

Botanical name

Fraxinus (green ash: F. pennsylvanica)

Type

Deciduous shade tree

Height

Green ash about 100 feet in the south of its range, typically half that in the north (USFS)

Native habitat

Mainly streamside; restricted to riparian areas at the western edge

Hardiness

Zones 6b to 7b across the service area

Common forms here

Green ash, Modesto ash, Raywood ash

Ash have opposite branches and compound leaves. Many planted ash are now old enough to need a professional look.

How do you identify an ash?

Branches and buds sit opposite each other in pairs, not alternating. Leaves are compound, with 5 to 9 leaflets on a central stem. Fall color is yellow in green ash and burgundy-purple in Raywood. Bark on old trees has a diamond pattern of interlacing ridges. Modesto ash tends to have a rounded crown and lighter foliage; Raywood has a narrower, upright habit with glossy leaves.

• Opposite branches and buds
• Compound leaves with several leaflets
• Diamond-pattern bark on older trees
• Winged, paddle-shaped seeds on female trees

Where does ash grow here?

Ash is a planted tree on valley and foothill lots in Reno (4,500 feet), Sparks (4,400 feet), Carson City (4,700 feet) and the Carson Valley (4,700 to 4,900 feet), in zones 6b to 7b. The Forest Service says green ash is mainly a streamside species, restricted to riparian areas in the westernmost part of its range, and has escaped into the wild in Utah and Colorado. In town it depends on lawn and drip water, since the nearest NOAA stations record 7 to 9 inches of precipitation a year.

What goes wrong with ash here?

Drought comes first. The Forest Service reports that green ash has survived drought in several areas but is a streamside species and the author cautioned against planting it on upland sites with fine-textured soil. A thinning top, small leaves and dead twigs in the crown signal water stress. See drought stress and dieback.

Wounds from mowers, cuts and storm breakage let decay in, and old ash drop large limbs in snow and wind. Co-dominant trunks that split from a V are common. A sound tree with a weak union can sometimes be held by cabling and bracing. Borers and cankers can also be involved; an arborist identifies the cause and we do not spray.

What does an arborist check on an ash?

We check the unions, the diamond-patterned bark for wounds and sunken patches, the crown for dead twigs and the root flare for lifted soil. An ash on a lot that has had its lawn replaced, its irrigation changed or its roots cut by trenching for a line is worth a closer look.

Pruning timing and removal

Dead wood and hazards come off at any time. Other pruning is usually done in late winter while the tree is dormant. Thin to reduce the weight of long limbs and take out deadwood. Do not top.

Removal is the usual answer for a tree that is mostly dead, has trunk decay or lifted roots, or has a split union over a house. A certified arborist assesses the tree on a free estimate. See large tree removal and dead wooding. For firewood, call the office.