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Publication #ENH231

Alnus rhombifolia: White Alder1

Edward F. Gilman and Dennis G. Watson2

Introduction

A North American native commonly found along streams, White Alder is a quick-growing tree (to 30 inches per year) reaching 50 to 75 feet in height, sometimes up to 100 feet, and has a spread of 30 to 40 feet. The deciduous four-inch-long, glossy leaves are dark green above and lighter below and appear just after the springtime display of the six-inch-long, greenish-yellow catkins. These flowers are followed by the appearance of brown, cone-like fruits which persist on the tree throughout most of the year and are quite popular for use in dried flower arrangements. White Alder creates an interesting specimen during the winter with a straight trunk, persistent fruits, attractive silver/grey bark, and slender, horizontal branches with pendulous tips. The crown takes on a pyramidal shape in youth becoming more oval with age. Any necessary pruning should be done in winter or early spring. Once chosen, the central leader dominates the tree forming a pyramidal crown shape.

Figure 1. 

Middle-aged Alnus rhombifolia: White Alder

General Information

Scientific name: Alnus rhombifolia
Pronunciation: AL-nus rom-bih-FOLE-ee-uh
Common name(s): White Alder
Family: Betulaceae
USDA hardiness zones: 8A through 11 (Fig. 2)
Origin: native to North America
Uses: street without sidewalk; parking lot island > 200 sq ft; tree lawn > 6 ft wide
Availability: not native to North America

Figure 2. 

Range

Description

Height: 50 to 75 feet
Spread: 30 to 40 feet
Crown uniformity: symmetrical
Crown shape: pyramidal, oval
Crown density: moderate
Growth rate: fast
Texture: medium

Foliage

Leaf arrangement: alternate (Fig. 3)
Leaf type: simple
Leaf margin: serrate
Leaf shape: elliptic (oval)
Leaf venation: pinnate
Leaf type and persistence: deciduous
Leaf blade length: 2 to 4 inches
Leaf color: green
Fall color: no color change
Fall characteristic: not showy

Flower

Flower color: yellow
Flower characteristics: not showy

Fruit

Fruit shape: elongated
Fruit length: .5 to 1 inch
Fruit covering: dry or hard
Fruit color: brown
Fruit characteristics: does not attract wildlife; not showy; fruit/leaves not a litter problem

Trunk and Branches

Trunk/bark/branches: branches don't droop; showy; typically one trunk; thorns
Pruning requirement: little required
Breakage: resistant
Current year twig color: brown
Current year twig thickness: thin
Wood specific gravity: unknown

Culture

Light requirement: full sun, partial sun or partial shade
Soil tolerances: clay; sand; loam; acidic; alkaline; occasionally wet; well-drained
Drought tolerance: moderate
Aerosol salt tolerance: unknown

Other

Roots: not a problem
Winter interest: yes
Outstanding tree: no
Ozone sensitivity: unknown
Verticillium wilt susceptibility: resistant
Pest resistance: sensitive to pests/diseases

Figure 3. 

Foliage

Use and Management

White Alder will grow easily in full sun or partial shade in any moist soil and will happily tolerate the wettest conditions. It is usually not grown or offered by nurseries in the eastern U.S. but is common in some areas of California.

Propagation is by fresh seeds or by cuttings.

Pests

White Alder is attacked and killed by the flatheaded borer in California. This borer is closely related to the bronze birch borer. Prune infested branches during late summer and fall when the infestation is visible and easy to detect and the beetle does not fly. Avoid pruning in the spring.

Tent caterpillars.

Diseases

No diseases are of major concern.

Footnotes

1.

This document is ENH231, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date November 1993. Revised December 2006. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.

2.

Edward F. Gilman, professor, Environmental Horticulture Department; Dennis G. Watson, associate professor, Agricultural Engineering Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.