Washington Palm Washingtonia robusta




Дата канвертавання28.04.2016
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Washington Palm

Washingtonia robusta

INTRODUCTION

Commonly seen at 40 to 50 feet but capable of soaring to 80 feet in height, Washington Palm is quickly recognized as the much-used, straight, singletrunked street palm of years past . The lower leaves persist on the tree after they die, forming a dense, brown, shaggy covering below the living, bright green, broad, fan-shaped leaves, giving it the common name of petticoat palm. These dead fronds are known to be a fire hazard and a popular bedding roost for rodents and, because of this, must be removed by law in some areas. The sharply barbed leaf petioles and tall, thin trunks make frond removal a rather unpleasant task, but some people think the rapid growth rate and statuesque appearance more than make up for this trouble.

GENERAL INFORMATION

Scientific name: Washingtonia robusta

Pronunciation: wosh-ing-TOE-nee-uh roe-BUS-tuh

Common name(s): Washington Palm, Mexican

Washington Palm

Family: Arecaceae

USDA hardiness zones: 9 through 11

Origin: not native to North America

Uses: wide tree lawns (>6 feet wide); medium-sized tree lawns (4-6 feet wide); narrow tree lawns (3-4 feet wide); specimen; sidewalk cutout (tree pit); residential street tree; no proven urban tolerance

Availability: generally available in many areas within its hardiness range

DESCRIPTION

Height: 60 to 90 feet

Spread: 10 to 15 feet

Crown uniformity: symmetrical canopy with a regular (or smooth) outline, and individuals have more or less identical crown forms

Crown shape: palm; upright

Crown shape: palm; upright

Crown density: open

Growth rate: medium

Texture: coarse


Foliage

Leaf arrangement: alternate; spiral

Leaf type: costapalmate

Leaf margin: entire

Leaf shape: star-shaped

Leaf venation: palmate

Leaf type and persistence: broadleaf evergreen; evergreen

Leaf blade length: >36 inches

Leaf color: green

Fall color: no fall color change

Fall characteristic: not showy
Flower

Flower color: white

Flower characteristics: showy; summer flowering
Fruit

Fruit shape: oval; round

Fruit length: < .5 inch

Fruit covering: fleshy

Fruit color: black

Fruit characteristics: does not attract wildlife; inconspicuous and not showy; no significant litter problem


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

Crown shaft: no
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: high

Aerosol salt tolerance: moderate
Other

Roots: surface roots are usually not a problem Winter interest: no special winter interest

Outstanding tree: not particularly outstanding Invasive potential: little, if any, potential at this time

Verticillium wilt susceptibility: not known to be susceptible

Pest resistance: long-term health usually not affected by pests
USE AND MANAGEMENT

Washington Palm makes a dramatic statement in the large landscape and creates a striking accent for multi-storied homes but often grows out of scale in most landscapes with one-story buildings because all of the fronds are at the top of the palm. It looks like a telephone pole with a green hat. Washingtonia filifera is a much better choice in unirrigated landscapes, since it grows more slowly, is shorter, and the trunk is thicker. Washington Palm needs full sun for best growth but will endure some shade while young. It will tolerate poor soil and drought, and is hardy to about 20-degrees F. Transplant with a large root ball to ensure survival. Washingtonia filifera is shorter, has a thicker trunk, and is better suited for planting in dry urban landscapes, such as in Texas. They reportedly suffer and often die from root rot when irrigated. Select Washingtonia robusta in an irrigated landscape and for the eastern U.S. Propagation is by seed.


Pests

Coconut mealybug, palm leaf skeletonizer, palm platid planthopper and a variety of scales infest this palm.


Diseases

Root rot can occur if this palm is planted on a wet site.




by Edward F. Gilman and Dennis G. Watson


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