Colorado blue spruce

Botanical name

Picea pungens

Type

Evergreen conifer, native to the Rocky Mountains

Height

Typically 70 to 115 feet in the wild; yard trees are often smaller

Trunk

Up to about 3 feet across

Lifespan

Long lived; the oldest recorded was about 600 years

Roots

Shallow; one study found 73.6 percent in the top 2 feet of soil

It is easy to spot: the symmetrical shape and silvery needles give it away. It is also one of the trees most likely to decline slowly on a dry lot.

How do you identify a blue spruce?

The needles are stiff, four-sided and sharp-pointed, about 1 to 1.25 inches long, and they roll between the fingers rather than lying flat. Color runs from green to a silvery blue. The crown is dense and cone-shaped, with horizontal to drooping branches that start low on the trunk, and the cones hang down.

• Stiff, sharp, four-angled needles that prick
• Silvery-blue to green foliage
• Spire-shaped crown with branches close to the ground
• Hanging cones

Where does it grow here, and why is it a hard fit?

In the Rockies the Forest Service puts it in canyons and moist slopes, from about 6,700 to 8,500 feet in Colorado canyons. In Northern Nevada it is a planted tree on lots from the valley floors (Reno at 4,500 feet, Carson City at 4,700 feet) up to Tahoe-basin yards above 6,200 feet. At the higher elevations the cold and the extra precipitation suit it better. The nearest valley NOAA stations record 7 to 9 inches of precipitation a year, while Glenbrook, at 6,350 feet, records about 18 inches.

The Forest Service notes that shallow roots restrict blue spruce to moist sites where water is near the surface, and that trees transplanted into drier conditions in the southern Rockies died of drought. On a hot, gravelly valley lot, it lives on irrigation.

What goes wrong with blue spruce?

Drought is the main one: the crown thins from the bottom and inside, then browns at the tips. The Forest Service also lists dwarf mistletoe, western spruce budworm, heart and root rots, cankers and, occasionally, bark beetles as problems for the species. Each needs an on-site look by an arborist to identify. Rot at the base is a safety question because a spruce with decayed roots can fall, see root and trunk decay.

Fire behavior matters near a house. The Forest Service says blue spruce is easily killed by fire and notes that slow self-pruning lets surface fires reach the crown, and University of Nevada Extension advises keeping evergreen woody plants at least 30 feet from the house. A spruce right against a wall is a good candidate for defensible space work.

Pruning and removal

Dead branches can come off any time. For other cuts, conifers are usually pruned in early spring and summer. Spruce does not regrow from bare wood, so heavy cutting leaves permanent holes; the useful work is deadwood, lifting a skirt that touches the ground and clearing branches off the roof and wires.

Removal is the usual answer when more than half the crown has died, when there is a dead top, when the base shows decay, or when the tree has outgrown the space. Blue spruce does not sprout from the stump. Ask for stump grinding if the spot needs to be used again. Our tree removal estimate is free, and a certified arborist assesses the job before work begins.