Differences in Blue Spruces & Black Spruces

Origins

• The blue spruce naturally grows in a limited, spotty range across the central and southern Rocky Mountains. The overall climate is cool and humid, with most of the limited rainfall occurring in summer. Blue spruces are remarkably drought tolerant, however. The black spruce grows across a massive range from interior Alaska, through most of Canada to Newfoundland. In the United States, black spruce inhabits the forests along the northern Great Lakes and eastward to New England. This species is very cold-tolerant, growing best in cool climates that are humid to dry. It gets much of its annual moisture from melting snowcover.

Size and Habit

• When mature, a blue spruce looks like a broad pyramid with horizontal branches radiating out from the trunk in all directions. Often reaching 30 to 60 feet tall and 10 to 20 feet wide in garden settings, in the wild it can attain a size up to 100 feet and 35 feet wide. By contrast, the black spruce develops a thin, irregular, spirelike to columnar silhouette with downward-angled branches that turn upward at their tips like an eyelash. It matures 30 to 65 feet tall and merely 6 to 10 feet wide.

Growing Locations

• Blue spruces grow best in cool or cold-winter climate regions that do not have long, hot or dry summers. Grow them in U.S. Department of Agriculture plant hardiness zones 2b through 8a. Likewise, the black spruce also prospers in cold winter and cool, short summer regions, but is more cold hardy that the blue spruce. Plant black spruces in USDA zones 1 through 6.

Cultural Insights

• Blue spruce is moderately slow-growing, but faster in pace compared with black spruce. Blue spruce is more tolerant of salt, air pollution and drought. Blue spruce also needs a well-drained soil to prevent root rot. Its root system is generally steadfast. By contrast, black spruce trees appreciate a very cool and moist soil, almost to the degree of being boggy. The root system is shallow because of its tendency to naturally inhabit wet soil areas, and therefore is more prone to toppling from winds. An ornamental drawback is that old cones and dead branches and twigs persist on black spruces, making them look tattered or sickly in gardens.