An aspen tree is the most widely distributed tree species in North America, ranging from Alaska to Newfoundland and down the Rocky Mountains to Mexico. Interestingly, Utah and Colorado is home to the largest portion of the natural acreage of aspen in the World. Aspen trees are described as an all important and community dependent "keystone species" within its natural range. Aspen trees are the most visible of western North American hardwoods providing understory biodiversity, wildlife habitat, livestock forage, specialty forest products, and highly desirable scenery.

Common Names: trembling aspen, golden aspen, quiver-leaf aspen, small-toothed aspen, Canadian aspen, quakie, popple 

Habitat: Aspen trees occupy pure stands on sandy gravelly slopes, the only transcontinental broadleaf tree growing from Newfoundland to California and Mexico. It is often associated with Douglas fir. An aspen tree is a pioneer tree after fires and logging, the most wind-sensitive leaf of any broadleaf species.

Description: The circular to triangular leaves gives this species its name, each leaf trembling in the slightest breeze at the end of a long, flattened stem. The thin, damage-prone bark is light green and smooth with bands of warty bumps. 

​Uses: furniture parts, matches, boxes, pulp

Aspen trees are affected by numerous insects, diseases and cultural problems. While there are plenty of good-looking aspen around the region, it also is the most common problem tree discussed in calls or samples brought to Colorado State University Cooperative Extension's Plant Diagnostic Clinic.

​Aspen trees are short-lived trees, as expected from their role in forest ecology. In the urban landscape, even properly cared-for aspen may not reach 20 years. Life spans can be shortened further by one or more of several insects or diseases that attack aspen. Fungal diseases, such as Cytospora or other cankers which attack the trunk, are common, as are diseases of the foliage such as rusts, or leaf spots. Of the many insects that attack urban plantings of aspen, oystershell scale, aphids and aspen twig gall fly are most prevalent."

Remember that aspens are very sensitive to many environmental problems and are host to more than five hundred species of parasites, berbivores, diseases, and other harmful agents. Aspens have been a disapointment to many when planted in the landscape.

Douglas Fir

Douglas-fir is not a true fir and has been a taxonomic nightmare for those trying to settle on a genus name. After changing names on numerous occasions the present scientific name Pseudotsuga menziesii now uniquely belongs to Douglas-fir.

To make things even more complicated two different varieties of the species are recognized. There is the P. menziesii var. menziesii, called coast Douglas-fir, and P. menziesii var. glauca called Rocky Mountain or blue Douglas-fir. 

The unusual cone is also unique with, forked, snake-tongue-like bracts extending from each scale. The tree is one of the dominant trees in the foothills of the Rocky Mountains, and up the slopes to medium altitudes. It has been transplanted successfully throughout most of the North American temperate zone.

Douglas-Fir's grow 40 to 60 feet and spreads 15 to 25 feet in an erect pyramid in the landscape. It grows to more than 200 feet tall in its native habitat in the West. Hardiness varies with seed source, so be sure it was collected from an area with suitable coldhardiness to the area in which it will be used.

Pests: Aphids infestations on small trees may be dislodged with a strong stream of water from the garden hose. Scale and bark beetles may infest Douglas-Fir, especially those under stress.

Diseases: Root rot can be a serious problem on clay and other wet soils. Needles infected by leaf cast fungi in spring turn brown and fall off. Several fungi cause canker diseases leading to branch dieback. Maintain tree health and prune out infected branches.

(Info courtesy of

Tree Information

Trees are an essential part of our communities, environment and comfort. To learn more about trees explore the information below.

In this section you can explore the various trees we typically plant and articles that we've published. We hope you'll find valuable information here, browse and enjoy.


 Copyright © 2021 Spalding Trees LLC, all rights reserved.

​Blue Spruce

Colorado Blue Spruce has a horizontal branching habit and grows taller than 75 feet in its native habitat, but is normally seen at 30 to 50 feet in landscapes. The tree grows about twelve inches per year once established but may grow slower for several years following transplanting. Needles emerge as a soft clump, changing to a stiff, pointed needle sharp to the touch. The crown form varies from columnar to pyramidal, ranging from 10 to 20 feet in diameter.

Scientific name: Picea pungens 
Pronunciation: PIE-see-uh PUN-jenz 
Common name(s): Colorado Spruce, Colorado Blue Spruce, Blue Spruce 
Family: Pinaceae 
USDA hardiness zones: 4 through 7 
Origin: native to North America 
Uses: screen; specimen; Christmas tree; no proven urban tolerance 
Availability: generally available in many areas within its hardiness range

Colorado Blue Spruce Description:

Height: 30 to 50 feet 
Spread: 10 to 20 feet 
Crown uniformity: symmetrical canopy with a regular (or smooth) outline, and individuals have more or less identical crown forms 
Crown shape: columnar; pyramidal 
Crown density: dense 
Growth rate: slow 
Texture: fine