In some areas, especially coastal areas of North America, you have the choice of two blue-tinted evergreens. Although blue spruce and blue atlas cedar are both evergreens and, as such, similar in many ways, the two trees have a number of notable differences.
Blue spruce has a columnar growth pattern with a tendency to grow upward until the branches reach a larger size. When the branches of a blue spruce reach a large enough size, they begin to droop down, but still maintain strong horizontal lines. Although the general growth pattern of a blue atlas cedar is also columnar, the trees can sometimes have a more unkempt look. As the branches grow, they bend toward the ground resulting in a weeping effect.
The needles of a blue spruce are of medium length, straight, and sharp. They grow outward from small branches and don't grow very long, and thus allow the shape of the underlying branch structure to be more visible in this species. Blue atlas cedars have a spiral needle arrangement where a number of needles grow outwards in a spiral pattern from a central point. This arrangement creates more of a sense of fullness with blue atlas cedar trees.
The difference in branch growth and needle arrangement make blue atlas cedar suitable for basic topiary, especially ball-shaped topiary. Blue spruce is less suited to topiary because of its lower needle density and readily visible branch structure.
Blue spruce can grow to between 50 and 75 feet high with a horizontal spread of around 25 feet. Blue atlas cedar are a slightly smaller tree, reaching between 40 and 60 feet in height with a spread of 30 to 40 feet. Because of the weeping branch patterns on many blue atlas cedar, they are best planted away from driveways or walkways.
Blue spruce are very hardy trees that can survive in more extreme climates. Blue spruce will grow well in zones 2 through 8, making them suitable for most parts of North America. Some coastal zones, like Florida, southern Texas and Louisiana, and parts of the Oregon and California coasts, may be too warm and humid for this tree to thrive. Blue atlas cedar are less hardy. They will grow well in zones 6 through 8, but will not do well in coastal areas where the blue spruce won't thrive.