Spruces (genus Picea – meaning pitch in ancient Latin) are usually tall, symmetrical, conical evergreen trees. The genus includes thirty-five species (half native to China), most of which are restricted to cooler regions of the northern hemisphere, growing at high altitudes in the southern Appalachians to New England or at higher latitudes in Canada and the higher elevations of Pacific coastal mountains and the Rocky Mountains. Washington Grove is at the very southern edge of the range where most spruce trees will thrive. The other main cultural requirement for most spruces is moist soil and good drainage. A warming climate may make spruces less desirable in our area.
Most spruces have strong, central trunks. They are distinguished from other evergreen trees by four sharp-pointed needles that whorl and radiate equally around the branch and have the look of a bristle brush. The needles are attached to the twig by tiny pegs that remain on the branch after the needle drops. The needles are attached singly to the branches, unlike pines, which have two to five needles per fascicle. Spruce cones are oblong and cylindrical. They tend to be attached to limbs mostly at the top of the trees and point downward.
The wood of spruces is typically strong for its weight. There are several spruce species important to the timber trade, the Christmas tree industry and to landscapers. However, the most common use is for pulp and paper production.
Norway Spruce (Picea abies)
Native to northern and central Europe, the fast-growing Norway spruce has been planted extensively and naturalized in colder parts of North America. Rockefeller Center’s annual Christmas tree is a Norway spruce, ranging in height between sixty-five’ and one hundred.’ In our area, they rarely reach greater than sixty feet tall and thirty feet wide. The wood has some interesting uses, such as for making sounding boards for musical instruments and spruce beer from new leafy shoots. Norway spruce is the most recognizable spruce variety in Washington Grove, where they are usually found singly. They are easy to spot by their generous size and by the shape of the pendulous branchlets descending from lateral branches (Photo #1). The large downturned cones are purple when immature, turning brown in the fall (Photo #2).
A common pest of Norway spruce are bagworms, strange caterpillars that develop in silken bags with bits of interwoven twigs and foliage (Photo #3). The exquisitely solitary females remain in their bags throughout their lives, expanding the bag as they grow. Males emerge from their bags for the sole purpose of mating with the females. A severe bagworm infestation can kill a young tree. Bags should be removed before the eggs hatch in June.
Colorado blue spruce (Picea pungens)
Of our eight native spruces, Colorado spruce is planted most commonly, the bluer the better for most nurseries. Native to the western U.S. (the state tree of Colorado and Utah), it is more drought tolerant than other spruces. The Colorado spruce is most familiar as an ornamental landscape tree. It is also often sold as a living Christmas tree, which includes a root ball that can be planted after the holidays. It’s also popular because it rarely sheds its needles indoors. A dwarf variety was planted front of the memorial bench at the southeast corner of Acorn Lane and Chestnut Streets (Photo #4).
A major problem of Colorado spruce in Washington Grove is Spruce Needle cast disease due to the fungus Rhizosphaera, which causes needles to turn brown and fall off. The disease gradually spreads upward and around the tree. Infected trees have few needles near the trunk and look thin, or see-through. Branches die if year-old needles are infected over a three- to four-year period (Photo #5). In contrast, the disease is inconsequential in natural forests. Norway spruce is relatively immune from severe infection. University of Minnesota Extension has a thorough description of how to manage the disease. Because these trees do not thrive in our area, making them more susceptible to disease, they are best avoided.