The Colorado spruce (Picea pungens) is the state tree of Colorado. Native to the western United States, this tree has many cultivars, most with a bluish tinge to their foliage. For that reason, Colorado spruce trees are often called "blue" spruces. The cultivars also range widely in their size and form. This tree is popular with home gardeners for its distinctive foliage color and is often used as a specimen tree or a Christmas tree, according to Ohio State University.
Colorado spruce trees vary slightly in their cold-hardiness, but in general, they grow well in U.S. Department of Agriculture (USDA) growing zones 2 through 7A. Native to the mountains of the western United States, these trees prefer temperate climates, with cool or cold winters and mild summers. They do not grow well in hot, humid climates.
Colorado spruce trees are usually found growing in sunny or partially shady locations. They prefer consistently moist soil, according to North Carolina State University, but are drought-tolerant when established. Picea pungens trees are found growing in just about any type of soil, from hard clay to acidic soils.
Colorado spruce trees have very sharp, stiff, evergreen needles. They average a little over an inch in length and radiate around the stem. This can make it painful to brush up against or grasp a branch with your bare hands. The needles are greenish blue, intensely blue or silvery blue, depending on the cultivar. The pine cones are long and slender, reaching 3 inches in length, and hang from the ends of the branches.
Colorado spruce trees can suffer from insect pest problems and diseases, according to North Dakota State University. The most common are fungal-based, including Rhizosphaera needle cast and Lirula needle blight, both of which cause the tree to drop its needles. Cytospora canker is a fungal disease that infects the wood rather than the needles, causing the wood to develop sunken, cracked areas. Prune off affected branches and use a fungicide in the early spring, before new growth develops, to prevent these diseases. Insect pests that commonly infest these trees are spider mites, scale, aphids and sawflies. Spray your tree with an insecticidal oil or soap if you notice an insect infestation on your tree. Follow the directions on the label of the fungicide and insecticide as per the age and size of your tree.
Cultivars of the Colorado spruce can range widely in appearance. P. pungens "Glauca Globosa" is a dwarf, blue-needled cultivar that presents more as a bush than a tree. It only grows to 3 feet tall, with a width of 5 feet. P. pungens "Backeri" is excellent for planting along the foundation of a house, and will grow to a maximum height of 12 feet and a width of 6 feet."Hoops" (P. pungens "Hoopsii") is a cultivar that has very showy, silvery blue needles. This tree is considered the best of the blue spruce cultivars, according to Ohio State University, and grows to a maximum height and width of 40 and 15 feet, respectively.