Blue spruce

The blue spruce (Picea pungens), also commonly known as Colorado spruce or Colorado blue spruce, is a species of spruce tree native to North America in Arizona, Colorado, Idaho, New Mexico, Utah and Wyoming. It is noted for its blue-green colored needles, and has therefore been used as an ornamental tree in many places far beyond its native range.
In the wild, Picea pungens grows to as much as 50 meters (164 ft) in height, but more typically 30 m (98 ft) tall. When planted in parks and gardens it most often grows 9 to 18 m (30 to 60 ft) tall with a spread of 3 to 6 m (10 to 20 ft). It has scaly grey-brown bark with a slight amount of a cinnamon-red undertone on its trunk, not as rough as an Engelmann spruce. On older trees the trunk bark will be deeply furrowed and scaly. The diameter of the trunk may reach as much as 1.5 m (4.9 ft).
Blue spruces are conifers with a pyramidal or conical crown when young, but more open and irregular in shape as they become older. The stout branches grow out horizontally in well defined whorls, but lower branches droop downwards as trees age. Young twigs never hang downwards and are yellow-brown in color.
The narrow, needle-like, evergreen leaves are quite sharply pointed and may be dull green, blue, or pale white. Each of the needles is four sided with stomata on every side, stiff, and 1.6–3 centimeters (3⁄4–1+1⁄4 in) long. The needles are attached radially to their shoots, but curve upward. The leaf buds are golden brown and cone shaped. The buds may be 6 to 12 millimeters (1⁄4 to 1⁄2 in) in size and the tip may either be blunt or pointed.
The pollen producing cones, more properly strobili, develop throughout the crown of blue spruce trees, but are more common in the upper half of the crown. Pollen cones are mainly yellow with a touch of red and average 1.5 cm (1⁄2 in) long. The seed cones begin growing in May or June and release their mature seeds in the autumn of the same year in which they start to grow. When young they are purple-brown in color. When fully mature they are light brown with thin, papery scales and are often curved. Overall they are longer than they are wide, between 8 and 15 cm (3 and 6 in) long, and circular in cross section. The seed cones are only found at the top of the tree. This helps to facilitate cross-pollination.
The seeds are dark brown. They average 4 mm in length with the papery wing extending beyond the tip almost twice this length.
The phytochemistry of the blue spruce is relatively little studied. The ripe seeds have a 1.17% yield of essential oils while the cones produce only 0.38% when steam distilled for four hours. The main component, over 40%, of the essential oils is limonene with β-Pinene and α-Pinene the next most significant.
Picea pungens was given its first valid scientific description by George Engelmann in 1879. He had previously named it Abies menziesii in 1862 and then as Picea menziesii in 1863 after, but both those names had already been used making them illegitimate names.
Picea, the genus name, is thought to come from the Latin word pix meaning "pitch", a reference to the typical sticky resin in spruce bark. The specific epithet pungens means "sharply pointed", referring to the leaves.
The most frequently used common name in English is blue spruce. It was first used for other trees in 1817 and is still used for any spruce tree with a glaucous blue color to their needles, but most frequently meaning Picea pungens. Though this is the most common name, in the wild only part of the population has the waxy blue-gray coating for which the tree is named. Less frequently, but still common, is Colorado blue spruce, a name first used in 1912. The usage of Colorado spruce dates to 1881, but is less frequent than the longer alternate. Occasionally encountered are the names Parry's spruce, prickly spruce, silver spruce, and white spruce. Blue spruces are also rarely called silvertip fir, but this name is also applied to Abies magnifica especially when sold as Christmas trees. In addition it is sometimes labeled as "Colorado green spruce" or "green spruce" by plant nurseries or tree farms.
Similar to the meaning of the scientific name, the Navajo name for this species is a compound c’ó deniní with c’ó meaning spruce and deniní meaning "it is sharp".
Blue Spruce occurs at high elevations, 1,830 to 2,740 meters (6,000 to 8,990 ft) in the forests of the South Central Rockies and 2,130 to 3,050 meters (6,990 to 10,010 ft) in the Southern Rocky Mountains. It grows in mesic montane conifer forests, often associating with Douglas-fir, ponderosa pine, or white fir. It has a riparian affinity, preferring moist soils such as those along streams or at the edges of wet meadows. The Douglas-fir or ponderosa pine only become associated with streams at lower, warmer elevations. It also may be found alongside the quaking aspen (Populus tremuloides) in the high mountain habitats of desert ranges in the Intermountain West.
Blue spruce usually grows in cool and humid climatic zones where the annual precipitation mainly occurs in the summer.
Blue spruce is most common in Colorado and the Southwest. The annual average temperature ranges from 3.9 to 6.1 degrees C (39 to 43 degrees F). And ranges from - 3.9 to - 2.8 degrees C (25 to 27 degrees F) in January. In July, the average temperature ranges from 13.9 to 15.0 degrees C (57 to 59 degrees F). The average minimum temperature in January ranges from - 11.1 to 8.9 degrees C (12 to 16 degrees F), and the average maximum temperature in July ranges from 21.1 to 22.2 C (70 to 72 degrees F). There is a frost-free period of about 55 to 60 days from June to August.
Annual mean precipitation generally vary from 460 to 610 mm (18 to 24 in). Winter is the season with the poorest rainfall, the precipitation is usually less than 20 percent of the annual moisture falling from December to March. Fifty percent of the annual precipitation occurs during the growing season of the plants.
Blue spruce is generally considered to grow best with abundant moisture. Nevertheless, this species can withstand drought better than any other spruce. It can withstand extremely low temperatures (-40 degrees C) as well. Furthermore, this species is more resistant to high insolation and frost damage compared to other associated species.
Blue spruce generally exists on gentle uplands and sub irrigated slopes, in well-watered tributary drainage, extending down intermittent streams, and on lower northerly slopes.
Blue spruce always grow naturally in the soils which are in the order Mollisols, and the soil will also be in the orders histosols and inceptisols in a lesser extent.
Blue spruce is considered as a pioneer tree species in moist soil in Utah.
Blue spruce seedlings have shallow roots that penetrate approximately 6 centimeters (2.5 in) into the soil during the first year of growth. Although freezing can't damage much in blue spruce, frost heaving will cause seedling loss. Shadows in late spring and early autumn minimize this frost heaving loss. Despite the shallow roots, blue spruce is able to resist strong winds. Five years before transplanting, the total root surface area of 2-meter-high trees was doubled by pruning the roots of blue spruce. It also increases the root concentration in drip irrigation pipeline from 40% to 60%, which is an advantage in landscape greening.
The blue spruce is attacked by two species of Adelges, an aphid-like insect that causes galls to form. Nymphs of the pineapple gall adelgid form galls at the base of twigs which resemble miniature pineapples and those of the Cooley's spruce gall adelgid cause cone-shaped galls at the tips of branches. The larva of the spruce budworm eat the buds and growing shoots while the spruce needle miner hollows out the needles and makes them coalesce in a webbed mass. An elongated white scale insect, the pine needle scale feeds on the needles causing fluffy white patches on the twigs and aphids also suck sap from the needles and may cause them to fall and possibly dieback. Mites can also infest the blue spruce, especially in a dry summer, causing yellowing of the oldest needles. Another insect pest is the spruce beetle (Dendroctonus rufipennis) which bores under the bark. It often first attacks trees which have blown over by the wind and when the larvae mature two years afterwards, a major outbreak occurs and vast numbers of beetles attack nearby standing trees.
The blue spruce is susceptible to several needle casting diseases which cause the needles to turn yellow, mottled or brown before they fall off. Various rust diseases also affect the tree causing yellowing of the needles as well as needle fall. Canker caused by Cytospora attacks one of the lower branches first and progressively makes its way higher up the tree. The first symptom is the needles turning reddish-brown and falling off. Meanwhile, patches of white resin appear on the bark and the branch eventually dies.
It is also relatively intolerant of light pollution and when planted near street lights or other outdoor lighting its preparation for winter can be delayed and parts of the tree may be damaged.
The native range of the blue spruce is largely in the Central and Southern Rocky Mountains and moist mountain valleys and canyons to the west. In New Mexico it only grows naturally in the higher mountain ranges of the state such as the Sandia–Manzano Mountains, Sangre de Cristo Mountains, and San Juan Mountains, as well as on Sierra Blanca Peak to the south. In Arizona the range is even more limited, growing in just Coconio and Apache counties. In Apache County it is found in the White Mountains in central eastern Arizona and the Lukachukai Mountains in the northeastern corner of the state. In Coconino County they only grow on the Kaibab Plateau. The blue spruce grows in every county in the western two-thirds of Colorado; approximately half of natural range of the species is in the mountains of Colorado. In Utah they are a locally common part of forests in the Uinta Mountains. West of the Uintas blue spruces are less frequent in canyons south of Salt Lake City.
The blue spruce has become naturalized outside of its native range. In North America has escaped from cultivation in the states of Minnesota and New York. It has also become established to some extent in many western and northern European countries including Iceland, Norway, Sweden, the United Kingdom, France, and Belgium. In middle and southern Europe it is found in Germany, Switzerland, Austria, the former Czechoslovakia, and mainland Italy. To the east it grows in European portions of Russia, the Caucasus, and Bulgaria.
The tallest documented blue spruce tree is an individual in the San Juan Mountains of southern Colorado in the Hermosa Creek area. When measured by Matt Markworth in 2015 it was 54.9 meters (180 ft) tall. Just three years later in 2018 it was threatened by the 416 Fire. Though the fire killed a shorter 50.4 m (165.5 ft) American champion tree with a larger trunk and crown spread the tall tree was spared due to being located in a sheltered valley.
Picea pungens and its many cultivars are often grown as ornamental trees in gardens and parks. It is also grown for the Christmas tree industry. It grows best in USDA growing zones 1 through 7, though it also does well in zones warmer than 7 where summer heat is moderate, as at San Francisco.
Common cultivars (those marked agm have gained the Royal Horticultural Society's Award of Garden Merit):
The Navajo and Keres Native Americans use this tree as a traditional medicinal plant and a ceremonial item, and twigs are given as gifts to bring good fortune. In traditional medicine, an infusion of the needles is used to treat colds and settle the stomach. This liquid is also used externally for rheumatic pains.
The blue spruce is the state tree of Colorado. It officially became Colorado's state tree on 7 March 1939 when House Joint Resolution 7 was enacted by the legislature. Previously a vote of the state's school children was taken on Arbor Day in 1892 expressing their preference for the blue spruce as the state tree.
From 1933 until 2014 the blue spruce was also the state tree of Utah. It was replaced by the quaking aspen because the aspen is a great deal more common than the blue spruce in Utah, making up 10% of the state's tree cover.