Picea pungens ‘Koster’

14 Oct

Picea pungens 'Koster' (08/10/2011, Horní Bečva, Czech)

Picea pungens ‘Koster’ (08/10/2011, Horní Bečva, Czech)

Position: Full sun 

Flowering period: May

Soil: Moist 

Eventual Height: 4-15m (Unpredictable)

Eventual Spread: 1.5-4m (Unpredictable)

Hardiness: 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a

Family: Pinaceae

Picea pungens ‘Koster’ is a medium sized evergreen conifer tree with a narrow conical growth habit. It’s glaucous foliage is silvery blue becoming grey-green with age. It’s leaves are rigid, needle like, arranged singly all round the shoots and are 15-30mm long. The monoecious flowers are ornamentally inconspicuous. The tree gives rise to narrow hanging cylindrical cones which are 4-10 cm in length, emerge a reddish to violet colour, maturing to a pale brown. They have leathery scales and are borne near the end of the shoots. The bark of the tree is grayish black, scaled  with glossy orange brown twigs. It’s trunk tapers rapidly.

Picea pungens ‘Koster’, commonly known as the Colorado Blue Spruce, is native to the Western United States. It is a plant that displays positive phototropism as well as negative gravitropism or geotropism in its stems as it reaches towards the light out of the seed. It is found in mountain valleys, but chiefly found near streams where moisture levels are high. Picea pungens was discovered in the Rocky Mountains, USA in  1861, eventually arriving in Europe in the late 19th Century. The variety Picea pungens ‘Koster’ displays a lack of uniformity between plants.

Picea pungens 'Koster' (08/10/2011, Horní Bečva, Czech)

Picea pungens ‘Koster’ (08/10/2011, Horní Bečva, Czech)

The etymological root of the binomial name Picea is derived from the Lain Pix meaning ‘pitch or tar’ in reference to the trees resin. Pungens is derived from the Latin meaning ‘prick, puncture or sting’ in reference to the leaves. 

The landscape architect may find Picea pungens ‘Koster’ useful as an attractive evergreen specimen parkland tree, due to its blue foliage and textured effect. It also make an effective windbreak or visual screen.

Ecologically, Picea pungens ‘Koster’ provides habitat and food for birds.

Picea pungens ‘Koster’ has been awarded the Royal Horticultural Societies award of garden merit in 1993.

Picea pungens ‘Koster’ prefers moist soils as it is commonly found beside streams in it’s native habitat. It will tolerate most soil pH although it prefers acid soils and dislikes chalky soils. It will also withstand short periods of drought (unusual for a Spruce).

Picea pungens ‘Koster’ requires little maintenance.

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