Widely grown as an ornamental specimen, the Colorado blue spruce (Picea pungens) grows up to 115 feet in height but tends to stay around 50 feet when planted in the home landscape. The tree attains a pyramid shape. Pale gray bark appears smooth on young trees but thickens with age. Needles appear in varying shades of bluish-gray to silver. Due to the tree's symmetrical appearance, it is gaining wide popularity as a Christmas tree, according to the National Christmas Tree Association.
Every 2 to 3 years the blue spruce produces a prolific crop of seeds. Seed production begins when the tree reaches 20 years of age. It reaches full seed-bearing potential between the age of 50 to 150 years. The blue spruce is monoecious and capable of self-pollination. Male strobili (flowers) emerge a brilliant red in color followed by the female red strobili. Seeds reach maturity in August and are dispersed widely by the wind.
Seeds often have a difficult time establishing naturally on the debris-covered forest floor. The seeds tend to be lightweight, so when they fall to the ground they are unable to reach the soil for germination to occur. Seedlings tolerate a wide range of soil and tend to grow rapidly once established. Once established, the tree grows around 12 inches per year, according to the U.S. Forest Service.
The root growth of seedlings tends to be quite shallow. In the first year the seedlings' root system penetrates only a little over 6 inches, according to the U.S. Forest Service. As the tree reaches maturity, its root system remains relatively shallow. Even with shallow roots, the tree rarely suffers from windfall and tends to be quite stable.
During the growth of the blue spruce seedling, it will tolerate moderately shady conditions, unlike other species of conifers. In its natural habitat, the tree grows best at elevations between 6,000 and 11,000 feet. The tree grows throughout regions of Wyoming, Colorado, Idaho, New Mexico, Utah and Arizona.
The blue spruce lives for over 600 years. By the age of 350 years, the tree has normally attained a trunk growth of around 22 inches in diameter. Currently, there are 38 named cultivars of blue spruce. For optimum growth, the tree should be planted in U.S. Department of Agriculture hardiness zones 4 to 7.