Autum Purple Ash

 

Autum Purple Ash

Fraxinus americana ‘Autumn Purple’

Figure 1. Young ‘Autumn Purple’ White Ash.

‘Autumn Purple’ White Ash1

Edward F. Gilman and Dennis G. Watson2

INTRODUCTION

‘Autumn Purple’ White Ash is a male tree

introduced in 1956, growing 40 to 50 feet tall and

perhaps 35 to 50 feet wide, and is a cultivar of the

species which is native to moist locations (Fig. 1).

The tree grows rapidly and is almost pyramidal with a

round top when young, but gradually slows down and

develops an oval shape. ‘Autumn Purple’ White Ash

prefers a sunny exposure where it will develop its

consistently-outstanding deep red, maroon or purple

fall color, whereas the species develops yellow or no

fall color. Fall color often comes earlier than on other

trees. I can not think of another tree with better, longlasting

fall color.

GENERAL INFORMATION

Scientific name: Fraxinus americana ‘Autumn

Purple’

Pronunciation: FRACK-sih-nus

uh-mair-ih-KAY-nuh

Common name(s): ‘Autumn Purple’ White Ash

Family: Oleaceae

USDA hardiness zones: 3B through 9A (Fig. 2)

Origin: native to North America

Uses: wide tree lawns (>6 feet wide); recommended

for buffer strips around parking lots or for median strip

plantings in the highway; shade tree; residential street

tree; no proven urban tolerance

Availability: generally available in many areas within

its hardiness range

DESCRIPTION

Height: 40 to 60 feet

Spread: 35 to 50 feet

Crown uniformity: symmetrical canopy with a

regular (or smooth) outline, and individuals have more

Crown shape: oval; round

Crown density: moderate

Growth rate: fast

Texture: medium

Foliage

Leaf arrangement: opposite/subopposite (Fig. 3)

Leaf type: odd pinnately compound

Leaflet margin: entire; serrulate

Leaflet shape: lanceolate; ovate

Leaflet venation: pinnate

Leaf type and persistence: deciduous

Leaflet blade length: 2 to 4 inches

Leaf color: green

Fall color: purple

Fall characteristic: showy

Flower

Flower color: green

Flower characteristics: inconspicuous and not

showy; spring flowering

Fruit

There is no fruit on this tree.

Trunk and Branches

Trunk/bark/branches: grow mostly upright and will

not droop; not particularly showy; should be grown

with a single leader; no thorns

Pruning requirement: needs little pruning to develop

a strong structure

Breakage: resistant

Current year twig color: brown; gray

Current year twig thickness: thick

Wood specific gravity: 0.60

Culture

Light requirement: tree grows in part shade/part sun;

tree grows in full sun

Soil tolerances: clay; loam; sand; acidic;

occasionally wet; alkaline; well-drained

Drought tolerance: moderate

Fraxinus americana ‘Autumn Purple’ — ‘Autumn Purple’ White Ash Page 3

Other

Figure 3. Foliage of ‘Autumn Purple’ White Ash.

Roots: surface roots can lift sidewalks or interfere

with mowing

Winter interest: no special winter interest

Outstanding tree: not particularly outstanding

Invasive potential: little, if any, potential at this time

Verticillium wilt susceptibility: susceptible

Pest resistance: very sensitive to one or more pests

or diseases which can affect tree health or aesthetics

USE AND MANAGEMENT

This is a good tree for large open areas with

plenty of open soil space and makes a good shade tree

for homesites if shade is needed on the roof. It is

somewhat adapted for use as a street tree with plenty

of soil space but extensive use may be unwise because

of potential insect and disease problems as the tree

gets older and because of its sensitivity to extreme

drought. Ash decline is one of its major problems and

is probably caused by a complex of conditions,

including a mycoplasma-like organism. It has taken

out many trees in some locations. However, one

advantage of ‘Autumn Purple’ is the lack of seeds.

Seeds are a constant nuisance on the species and can

limit the species’ usefulness as a street tree.

Ash which have not been properly pruned can

break apart in wind storms, but White Ash has better

branch structure than seedling Green Ash. ‘Autumn

Purple’ reportedly has better structure than the species

with many closely-spaced branches. Be sure to space

major branches along the trunk and remove those

which are vigorously growing upright with narrow

branch crotches. Ash also has a tendency to produce

vigorous main scaffold branches opposite each other

on the trunk. Remove one so there is only one at each

position on the trunk. Some problems with graft

incompatibility have occurred with cultivars of White

Ash causing tree failure and breakage as the tree

grows. Select trees propagated on their own roots and

avoid those grafted or budded to Green Ash.

Grow Ash in the full sun or partial shade

preferably in a moist site although the tree does

withstand some drought. Growth will be best in

slightly acidic, neutral or slightly basic soil pH.

Pests

Borers can kill trees. The most common borers

infesting Ash are Ash borer, lilac borer and

carpenterworm. They can infest and ruin even

vigorously growing trees but are most common on

recently transplanted and trees stressed from other

problems. Ash borer bores into the trunk at or near

the soil line causing tree dieback. Lilac borer causes

swellings on the trunk and limbs where the insect

enters the tree. The carpenterworm larvae bore into

the heartwood but come to the outside of the tree to

push out frass and sawdust. Heavily infested trees can

be severely weakened. Keep trees as healthy as

possible by fertilizing regularly and watering during

dry weather.

Aphids are often seen but are usually not serious.

In late summer, fall webworm covers branches

with webbing. The nests in branches close to the

ground can be pruned out when first noticed.

Fraxinus americana ‘Autumn Purple’ — ‘Autumn Purple’ White Ash Page 4

The Ash flower-gall looks like a disease but is

actually a mite problem. The mites feed on the

flowers causing abnormal growth. The galls dry out

and persist on the tree into winter.

Diseases

The most serious problem is Ash decline or

dieback which has a variety of causes, some poorly

understood. The rest of the diseases listed below are

usually not serious.

A rust disease causes distorted leaves and swollen

twigs. Small, yellow, cup-like structures, producing

yellow spores, appear on the infected areas. Controls

are usually not needed.

A number of fungi cause leaf spots on Ash. The

disease is worse in wet years and is partially controlled

by gathering and disposing of diseased, fallen leaves.

Anthracnose is also called leaf scorch and leaf

spot. Infected parts of the leaves turn brown,

especially along the margins. Infected leaves fall

prematurely. Rake up and destroy infected leaves.

Chemical controls are not practical or economical on

most large trees.

Canker diseases cause branch dieback and death of

the tree when the trunk is infected. Try to keep trees

healthy with regular fertilization.

Powdery mildew makes a white coating on the

leaves.

Ash ring spot virus causes chlorotic yellow or

reddish spots or rings on the leaves. Infected trees

may be stunted and dieback but this usually does not

happen.

Verticillium wilt causes branches of infected trees

to wilt and die, eventually the entire tree may die.

Keep trees healthy and fertilize infected trees with

high nitrogen fertilizer to suppress disease symptoms.

 
 
 

1 Comment

  1. Deb says:

    We have a Purple Ash and we live in West Des Moines, Iowa.
    Thought we had a disease but it must be the mite problem. The lower half of the tree has those yellow green clumps/galls look like disease but I read it is a mite problem. They wont hurt my tree cause I love this tree and would hate to loose it?

 
 

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