Colorado Blue Spruce
Picea pungens Engelm.
Description:
Colorado blue spruce, or blue spruce, is an attractive tree often
used for Christmas trees or as ornamentals, particularly in the
eastern United States and Europe. It is the official state tree of
both Colorado and Utah. The species generally reaches a height of
65-115 feet at maturity with a diameter of 2-3 feet. It has a narrow,
pyramidal shape and cone-shaped crown. As trees become older, they
often take on a more irregular appearance. While blue spruce grows
relatively slowly, it is long-lived and may reach ages of 600-800
years.
Leaves (needles) are 1-1 1/2 inches long on lower branches but
somewhat shorter on upper branches. They are 4-sided and have a very
sharp point on the end. It is this point which gives the species its
name "pungens", from the Latin word for sharp as in puncture wound.
Needles are generally dull bluish-gray to silvery blue and emit a
resinous odor when crushed. Some trees have a more distinct
bluish-white or silvery-white foliage. The cultivated variety 'glauca'
is noted for this type of coloration. Nursery managers also select for
"shiners" which demonstrate this very desirable characteristic.
Needles occur on small peg-like structures on the twig called
sterigmata. The sterigmata persist on the twigs after needles have
fallen, which is usually after the third or fourth year.
Both male and female flowers (strobili) occur in the same tree,
although in different locations. Pollination occurs in late spring and
cones mature in one season. In the fall, cones are 2-4 inches long and
turn chestnut brown with stiff, flattened scales. Cones generally
persist on the tree for one to two years after seed fall.
The bark is thin becoming moderately thick with age. It is somewhat
pale gray in small flattened scales when young, then turns reddish
brown and furrowed with age.
Blue spruce is moderately shade tolerant and grows best in deep,
rich, gravely soils, often along stream banks and other sites with
high moisture levels. It usually does not occur in large stands but is
found in small groves or in association with Douglas-fir, lodgepole
pine, Engelmann spruce or ponderosa pine. A deep penetrating root
system makes the species resistant to being blown over.
Major pests include the western spruce dwarf mistletoe, spruce bark
beetle, and spruce budworm. Trees infected with mistletoe typically
develop abnormal masses of branches called "witches brooms". With
severe infestations, trees may be killed.
Blue spruce is finding increasing popularity as a Christmas tree as
a result of its symmetrical form and attractive blue foliage. The
species has an excellent natural shape and requires little shearing.
Additionally, needle retention is among the best for the spruces. Its
popularity as an ornamental leads many consumers to use blue spruce as
a living Christmas tree, to be planted after the holiday season.
Range:
Blue spruce occurs naturally from western Wyoming and eastern Idaho
southward through central Colorado and Central Utah. The southern
limits are New Mexico and Arizona. It occurs at elevations of 6,000 to
11,000 feet; generally at higher elevations in the more southern
areas.
Propagation:
Most propagation is by seed but blue spruce can be grafted or grown
from rooted cuttings. Vegetative propagation is more often used to
perpetuate the rarer, more desirable forms of the species. Picea
abies or Picea pungens are preferred rootstock for
grafting.
Over 70 cultivated varieties have been named.
Uses:
The wood is light to pale brown in color and is lightweight, soft,
and brittle. The lack of natural pruning leads to boards often being
full of knots. Blue spruce grows in relatively inaccessible locations
leading to its not being commercially important as a timber species.
The wood is suitable, however, for posts, poles, and fuel.
Blue spruce has limited value to wildlife but does provide cover
and seeds for squirrels, rodents and some birds.
In the western United States, the species has found some use in
shelterbelts.
Prepared by Dr. Craig R. McKinley, North Carolina State University
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