Colorado blue spruce is one of the most recognizable evergreens in North America, a stiff, symmetrical conifer whose silvery-blue needles make it a fixture of yards, parks, and holiday displays from coast to coast. It is also the official state tree of Colorado, and it began life as a tree of high, cool, dry mountain forests.
That origin explains both its strengths and its problems. In the Rockies it thrives on cold winters and low humidity, but in warmer, wetter regions it is prone to needle and canker diseases, and the University of Maryland Extension no longer recommends planting it in that state.
This guide covers how the tree is classified, where it comes from, why it is blue, which cultivars are worth knowing, and what it takes to keep one healthy.
Botanical Classification
Colorado blue spruce belongs to the pine family, in the spruce group, and it goes by several names, including Colorado spruce, blue spruce, and silver spruce. Its scientific name refers to the sharp, pointed needles, which are stiff, four-sided, and strong enough to prick a hand that grabs a branch.
The word “blue” needs a caveat. The University of Massachusetts Amherst Extension notes that the blue color is popular and common in cultivars, but the green form is more common in the wild. Cornell University’s Woody Plants Database adds that color is a very variable trait and that most blue-needled cultivars are propagated asexually, which is why a seed-grown tree may turn out green while a named selection stays reliably blue.
Brief History
Colorado’s State Archives records that the tree was first discovered on Pikes Peak in 1862 by the botanist C.C. Parry and was named by George Engelmann in 1879. Colorado schoolchildren voted for it as the state tree on Arbor Day in 1892, choosing it over white fir by more than 2 to 1 according to USA Symbol, but the General Assembly did not make the choice official until March 7, 1939. The Colorado State Archives describes it as known for its stately, symmetrical form and its silver-blue color.
Colorado is not the only state to have claimed it. According to USA Symbol, blue spruce was also Utah’s state tree from 1933 to 2014. Meanwhile, nurseries carried it far beyond its mountain home, and it became one of the most widely planted ornamental conifers in the country.
Picea, the genus name, is thought to come from the Latin word pix meaning “pitch”, a reference to the typical sticky resin in spruce bark. The specific epithet pungens means “sharply pointed”, referring to the leaves. George Engelmann provided the first valid scientific description of Picea pungens in 1879. The most frequently used common name in English is “blue spruce,” which was first used for other trees in 1817. “Colorado blue spruce” was first used in 1912, and “Colorado spruce” dates back to 1881.
Identifying Characteristics
The needles are the giveaway. They are borne singly, about 1 to 1.25 inches long, four-sided, very stiff, and sharp pointed, and they extend at right angles all around the twig. Iowa State University notes that the bluish color is especially distinct on new growth, and Utah State University’s TreeBrowser adds that the needles are very fragrant when crushed. The UMass Extension describes them as ranging from gray-green to blue-green and as four-sided with 6 stomatal lines on each side.
The cones hang down, are light chestnut-brown, and measure about 2.5 to 4 inches long, with papery scales that are slightly round-toothed at the tip. The bark is light to dark gray in thin scales, developing wide, thick ridges on older trees. The Utah State University TreeBrowser also notes that the tree is slow growing and that its wood is of minor importance.
In shape, the tree forms a regular narrow to broad pyramid with stiff, horizontal branches that reach the ground, and it is very dense. Iowa State cautions that it often becomes open, poor, and dingy in old age.
Native Range and Habitat
Blue spruce is native to the central and southern Rocky Mountains and the intermountain West. In Colorado it grows in small, scattered groves or singly among ponderosa pine, Douglas fir, alpine fir, and Engelmann spruce, according to the state archives. In the northern part of its range it grows at elevations of 6,000 to 9,000 feet, and in the southern part at 8,000 to 11,000 feet.
The UMass Extension describes it as native to high-elevation forests of the intermountain United States and hardy in zones 2 to 7, while Cornell lists it as hardy to zone 3b and tolerant of salt spray. Iowa State says it prefers rich, moist soil in full sunlight but is very adaptable.
Why It Is Blue
The blue color comes from a waxy coating on the needles. The wax appears to help protect the tree from harsh mountain sunlight and to conserve water. In wet climates the wax can be partly lost, and the blue tends to dull.
The color is also most distinct on the newest growth. Some buyers purchase a plain Colorado spruce expecting a blue tree year-round and find it green by spring, which is why it pays to buy a named blue cultivar.
Size and Growth Rate
Blue spruce is a slow to moderate grower. Iowa State reports growth of 30 to 50 feet after 35 to 50 years, and a mature height of 30 to 60 feet and a width of 10 to 20 feet under average landscape conditions. In the wild, trees can reach 90 to 135 feet tall and 20 to 30 feet wide.
The tree is also slow to reproduce. It begins bearing seed at around 20 years, reaches its best seed production between 50 and 150 years, and produces full crops of cones only every 2 or 3 years. That long timeline is a reminder that a blue spruce is a long-term investment.
Popular Cultivars
Growers have named a great many selections, and one garden guide counts nearly 100, not all of them blue. Cornell’s list highlights several of the best known. ‘Hoopsii’ has glaucous blue needles and a dense, pyramidal form, ‘Thompsenii’ has silver-blue foliage and a symmetrical habit, and ‘Iseli Fastigiata’ is an upright, narrow form with strong blue foliage.
The Purdue Arboretum describes ‘Hoopsii’ as one of the most striking conifers in color and habit, reaching 30 to 50 feet tall and 15 to 20 feet wide, with some drought tolerance. It cautions that it must be used with restraint, because the strong blue does not combine well with other plantings, and that it has some susceptibility to spruce gall adelgid.
For small yards, ‘Fat Albert’ is a popular choice. The NC State Extension Gardener Plant Toolbox says it was first selected as a seedling at the Iseli Nursery in Boring, Oregon, and that it reaches 8 to 15 feet tall and 7 to 10 feet wide, with a broad pyramidal shape, dense branches, and steel-blue needles. Cornell also lists prostrate, sprawling forms and a foxtail form that adapts better to hot summers than other types.
Wildlife Value
Blue spruce is more than a decorative tree in the Rockies, where it provides habitat for wildlife. Colorado arborists note that various species of Colorado wildlife depend on blue spruce, and that browsers such as deer often eat its foliage.
The UMass Extension adds that spongy moth caterpillars have been observed feeding on blue spruce needles during outbreaks, when their favored hosts run short. It is a useful reminder that even a tree with stiff, prickly needles is not immune to insects.
Landscape Uses
Blue spruce works best as a specimen tree, where its shape and color can stand on their own. Utah State calls it a beautiful, slow-growing tree but advises giving it enough room, since it can eventually get quite tall and wide, and it notes that wind-throw can be a problem. The tree has intermediate shade tolerance.
The NC State Extension recommends smaller cultivars such as ‘Fat Albert’ for mass plantings, foundations, lawns, walkways, and privacy screening. Because the blue is so strong, the Purdue Arboretum’s advice to use it with restraint applies to the species as well as to individual cultivars.
Growing Considerations
Blue spruce prefers rich, moist soil in full sun, according to Iowa State, and it does best in cool climates. Utah State cautions that it may not do well with extreme heat or hot, dry winds. The NC State Extension notes that, as blue spruce matures, it becomes more drought tolerant and is overall more drought tolerant than other spruces.
Cornell recommends transplanting balled-and-burlapped trees in spring or fall. Site selection matters more than most gardeners expect. Penn State Extension advises choosing a site that avoids drought-prone spots and asking whether it can supply the water a specimen 50 to 60 feet tall will need. It also recommends spacing trees and controlling weeds to provide free air circulation, which helps limit needle disease.
Climate is the biggest limit. The UMass Extension notes that blue spruce does better in cooler, more northern climates. The University of Maryland Extension states that Colorado blue spruce is no longer recommended for planting in Maryland, since summers there are too hot and humid, and winters too warm.
Pests and Diseases
Two fungal diseases cause most of the trouble. Needle cast is the most common problem seen on blue spruce samples at the Iowa State University Plant Disease Clinic, and the Morton Arboretum says blue spruce is particularly susceptible and can be severely damaged. Infection generally begins in spring on the needles of the lower branches, and year-old needles turn lavender or purplish and carry tiny black fruiting structures on the underside. The disease then works upward through the tree, and the UMass Extension notes that although needle cast does not kill a tree on its own, it contributes to decline and death.
Canker is the second problem. The Morton Arboretum calls it the most prevalent and destructive fungal disease of Norway and Colorado blue spruce, and it rarely affects trees younger than 15 to 20 years. It is a stress-related disease, worst on trees hit by drought, insect damage, crowding, or mechanical injury, and its signs include lower branch dieback and heavy resin flow. The University of Arkansas Extension suggests slowing it with extra water in dry weather and pruning infected branches while the tree is dormant, disinfecting pruners between cuts.
Insects add to the list. The UMass Extension notes that spruce spider mites cause fine yellow stippling, and that galls at the twig tips, produced by gall adelgids, can damage needles. Weir’s cushion rust is a minor but conspicuous disease.
Key Takeaways
The most common blue evergreen tree or shrub in the landscape is the Colorado blue spruce (Picea pungens). The blue spruce, also commonly known as Colorado spruce or Colorado blue spruce, is a species of spruce tree native to North America in Arizona, Colorado, Idaho, New Mexico, Utah and Wyoming.
It grows up to 100 feet tall in the wild, and nursery trees reach 60 feet tall. It is often called the Colorado blue spruce because it is found throughout the state, and because it is Colorado’s state tree. Hardy in U.S. Department of Agriculture plant hardiness zones 2 through 8, the blue spruce will live for many years if cared for properly.
In the wild, the Colorado blue spruce can live 200 years or more. In the home landscape, it usually stays healthy for about 40 to 60 years, after which its health begins to fail. Once established, it becomes more drought-tolerant, which allows it to survive in areas with less frequent rainfall.
This spruce does best in cooler climates and cannot tolerate heat and humidity. It may tolerate the summer weather in the North Carolina mountains. This tree can be grown in average, well-drained soils in full sun, although it will tolerate some shade. It prefers rich, moist soil in full sunlight. Young trees should be kept consistently moist and not allowed to dry out. As this spruce matures, it becomes more drought tolerant and is overall more drought tolerant than other spruces. It has a slow to medium growth rate.
The Colorado Blue Spruce (Picea pungens) is primarily native to the central and southern Rocky Mountains of the western United States. Its range extends from southern and western Wyoming, eastern Idaho, south to Utah, northern and eastern Arizona, southern New Mexico, and central Colorado. It has also been reported in isolated locations in north-central Montana1.
This tree thrives in a climatic zone that is generally cool and humid, with most of the annual precipitation occurring in the summer. The mean annual temperatures where the blue spruce is most commonly found range from 3.9° to 6.1°C (39° to 43°F), with a January mean of -3.9° to -2.8°C (25° to 27°F) and a July mean of 13.9° to 15.0°C (57° to 59°F). The frost-free period from June to August is about 55 to 60 days1.
The Colorado Blue Spruce grows best with abundant moisture but can withstand drought better than any other spruce. It can also endure extremely low temperatures (-40°C; -40°F) and is more resistant to high insolation and frost damage than other associated species.