Blue spruce trees (Picea pungens), also called Colorado spruce or Colorado blue spruce, is a coniferous evergreen tree native to the Western United States. Valued by homeowners in North America and Europe for its ornamental qualities, this species works well in mass plantings, as a specimen or as an evergreen shade tree.
Blue spruce trees are usually between 30 and 65 feet in height with a 15- to 25-foot spread, but some trees reach heights of 120 feet. They have pyramidal forms with stiff lower branches that cover the entire trunk and extend to the ground. Young trees have dense foliage comprised of four-sided, rigid greenish- or bluish-green needles, while older trees tend to have an open conical form. They yield ornamentally unimportant flowers, followed by narrow, 5-inch-long medium-brown cones.
Blue spruce trees are available in a number of cultivars. The Mission Blue and Hoopsii spruce trees have blue needles, while the Montgomery is a blue-needled dwarf variety. Glauca Pendula or Glauca Prostrata is a sprawling ground cover selection. Several other cultivars include Koster, which has silvery-white or bluish-white needles and heavy, drooping branches; Aurea, a selection with yellow-gold foliage; and Hunnewelliana, a dwarf cultivar with light- green needles.
Caring for Blue Spruce
Blue spruce trees are cold hardy in U.S. Department of Agriculture hardiness zones 2 through 7a. Although these trees can adapt to a variety of soil types, they grow best in well-drained, nutrient-rich, moist loamy soil with a pH level between 6.0 and 7.5. They are more drought-tolerant than many other spruce trees, but they cannot tolerate soggy or flooded soil. Blue spruce trees require full sunlight; they are not shade-tolerant. They grow slowly, but can live as long as 600 years.
Pests and Problems
Insect pests such as the western spruce budworm defoliate blue spruce trees by feeding on the needles and emerging buds. Spruce aphids and spider mites drain sap from the needles, while flat-headed borers and spruce beetle larvae feed on the wood below the bark. Several diseases include Leucocytospora kunzei, an infection that creates areas of diseased bark on blue spruce branches and causes branch dieback; Armillaria mellea causes root rot; and Phytophthora cinnamoni, or damping-off, destroys infected seedlings.