The blue spruce, green spruce, white spruce, Colorado spruce, or Colorado blue spruce, with the scientific name Picea pungens, is a species of spruce tree. It is native to the Rocky Mountains of the United States. Its natural range extends from northern New Mexico through Colorado and Utah to Wyoming and into far southwest Montana, but it has been widely introduced elsewhere and is used as an ornamental tree in many places far beyond its native range. The blue spruce has blue coloured needles and is a coniferous tree.
In the wild, Picea pungens grows to about 23 m (75 ft), but when planted in parks and gardens it seldom exceeds 15 m (49 ft) tall by 5 m (16 ft) wide. It is a columnar or conical evergreen conifer with densely growing horizontal branches. It has scaly grey bark on the trunk with yellowish-brown branches.
Pests and diseases
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.
- 'Glauca Globosa'agm - shrub from 3–5 feet (0.91–1.52 m) in height
- 'Fat Albert' - compact perfect cone to 10 feet (3.0 m) of a silver blue color
- 'Glauca Jean's Dilly' - shrub from 3–6 feet (0.91–1.83 m) in height
- 'Glauca Pendula' - drooping branches, spreads to about 8 feet (2.4 m) wide by 4 feet (1.2 m) tall
- 'Hoopsii' agm
- 'Baby Blue Eyes'
- 'Baby Blue' 
The Navajo and Keres Native Americans used 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. Early people used their wood for building.
- A. Farjon (2013). "Picea pungens". The IUCN Red List of Threatened Species. IUCN. 2013: e.T42333A2973433. doi:10.2305/IUCN.UK.2013-1.RLTS.T42333A2973433.en. Retrieved 13 January 2018.
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- USDA Accessed 2012-12-01
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- Cranshaw, W. S. (2013-06-13). "Scale Insects Affecting Conifers". Colorado State University Extension. Retrieved 2013-10-05.
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- "RHS Plant Selector - Picea pungens 'Globosa'". Retrieved 27 May 2013.
- Missouri Botanical Garden: Picea pungens 'Glauca Globosa'
- Missouri Botanical Garden: Picea pungens Fat Albert
- Missouri Botanical Garden: Picea pungens 'Glauca Jean's Dilly'
- Fine Gardening Plant Guide: Picea pungens ‘Glauca Pendula'
- "RHS Plant Selector - Picea pungens 'Hoopsii'". Retrieved 27 May 2013.
- "RHS Plant Selector - Picea pungens 'Koster'". Retrieved 27 May 2013.
- "Missouri Botanical Garden - Picea pungens 'Baby Blueeyes'".
- "Washington State University - Picea pungens 'Baby Blueeyes'".
- "West Montrose Farms Ltd - Picea pungens 'Baby Blue'".
- U. Michigan-Dearborn: Ethnobotany Accessed 2012-12-01
- Conifers.org: Picea pungens (blue spruce) description
- Lady Bird Johnson Wildflower Center NPIN — Native Plant Information Network
- Interactive Distribution Map of Picea pungens
- Picea pungens — U.C. Photo Gallery