Blue spruce (Picea pungens): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table. Two related pages cover agents the handbook names on this spruce: Cooley spruce gall and spruce budworm.

At a glance

Item	What the source records
Scientific name	Picea pungens Engelm., pine family (Silvics and PLANTS, symbol PIPU)
Other names, Silvics	Colorado blue spruce, Colorado spruce, silver spruce and pino real
Native status, USDA PLANTS	Native in the lower 48 states; introduced in Canada
Largest on record, Silvics	154.4 cm (60.8 in) in breast-height diameter and 38.4 m (126 ft) tall, on the Gunnison National Forest, Colorado, per the 1982 National Register of Big Trees
Weight table	Not published for blue spruce: NRS-38 lists it only in Table 4, the reference species table, with specific gravities assigned from the average of the same genus in Table 1A (footnote a), 0.36 for wood on a green volume basis and 0.39 at 12 percent moisture content, and gives no green weight per cubic foot. The Wood Handbook strength table has no row for it

Native range and climate

The Silvics of North America handbook (Agriculture Handbook 654, Volume 1, 1990) says blue spruce is native mainly to the central and southern Rocky Mountains. The range runs from southern and western Wyoming and eastern Idaho south through Utah, northern and eastern Arizona and southern New Mexico, with central Colorado in the middle, and the handbook reports it in isolated places in north-central Montana. It describes a generally cool, humid climate with most precipitation in summer, mean annual temperatures of 3.9 to 6.1 degrees C (39 to 43 degrees F) in Colorado and the Southwest, and annual precipitation of 460 to 610 mm (18 to 24 in). Silvics says that although blue spruce grows best with abundant moisture, it can withstand drought better than any other spruce and can take temperatures down to minus 40 degrees C (minus 40 degrees F).

Soils, sites and forest cover

The handbook says the soils are young and vary widely, mostly Mollisols and to a lesser extent Histosols and Inceptisols, with a pH of 6.8 to 7.2. Blue spruce is found on gentle upland and subirrigated slopes, in well-watered tributary drainages, along intermittent streams and on lower north-facing slopes, at 1,830 to 2,740 m (6,000 to 9,000 ft) in the north of its range and 2,130 to 3,050 m (7,000 to 10,000 ft) in the south. Its sites are wetter than those of Rocky Mountain ponderosa pine and warmer than those of Engelmann spruce and subalpine fir. It is the principal species of the Blue Spruce forest cover type (Society of American Foresters type 216) and a minor associate in four others. Silvics says it is seldom found in large numbers, but on streamside sites it is often the only conifer present. Narrowleaf cottonwood and quaking aspen are its most common hardwood companions.

Cones, seed and seedlings

Blue spruce is monoecious. The handbook says pollen is shed in May or June depending on altitude, a female cone has 175 to 225 scales with the potential for 350 to 450 seeds, and cones mature in August of the first year with seed shed from early to late September and into winter. Good to prolific seed production gives full crops every 2 or 3 years, some years in between failing completely, and seed bearing starts at 20 years, with the best seed-bearing age 50 to 150 years. Most seeds fall within 90 m (300 ft) of the upwind timber edge. Silvics says natural reproduction is scanty, mostly confined to exposed mineral soil with side shade and overhead light, and that seed once thought to be dormant germinates promptly without prior stratification. It calls early seedling growth very slow, the tallest of 50 populations in a Michigan nursery study averaging 15.7 cm (6.2 in) at 2 years. Natural vegetative reproduction has not been reported and the tree does not sprout from stump or root.

Growth, age and roots

Silvics describes blue spruce as apparently long lived, surviving 600 years or more, with slow diameter growth: trees 10 to 13 cm (4 to 5 in) across may be 125 to 135 years old and those 46 to 56 cm (18 to 22 in) across 275 to 350 years old. Seedlings are shallow rooted, with roots only 6.4 cm (2.5 in) deep in the first year, and the handbook says mature trees also have a relatively shallow root system but are decidedly windfirm. It classes shade tolerance as intermediate, the middle of five categories for western conifers: less tolerant than subalpine fir, Engelmann spruce and white fir, similar to Douglas-fir and more tolerant than ponderosa pine, lodgepole pine and aspen. Blue spruce is described as occurring in various successional stages, from pioneer to climax, and as pioneer on wet soils in Utah.

Damaging agents the handbook names

Cone and seed insects. The spruce seed chalcid, spruce seed moth, cone cochylid and spruce coneworm are named. Silvics says larvae of two of these destroy up to 10 percent of the seeds, and that insect damage is not heavy.
Foliage and twig insects. Western spruce budworm feeds on old needles in late April, mines buds and defoliates new growth, and heavy repeated attacks kill the tree. Spruce needle miners are called less serious. The Cooley spruce gall aphid and pine leaf aphids cause cone-shaped galls, the first of consequence on seedlings and saplings. Green spruce aphids and the white pine weevil feed on terminal twigs.
Bark and wood insects. The spruce beetle is found on blue spruce, twig beetles may attack injured trees, and ambrosia beetles and a flatheaded borer attack the wood.
Diseases. Silvics names damping-off and Cylindrocladium root rot that kill new seedlings, and nematodes and snow molds as nursery problems. Leucocytospora kunzei (Cytospora) canker may affect one-fourth to one-half of the branches of blue spruce, is usually not fatal, but branch loss dramatically reduces the looks of landscape trees. Phomopsis occulta causes a tip blight. Western spruce dwarf mistletoe raises mortality in infected stands two to five times over healthy stands, with up to 40 percent 10-year volume loss in heavily infected trees. Needle rusts, the needle cast Rhizosphaera kalkhofii, a witches' broom rust, root rots from Armillaria mellea and Inonotus tomentosus, and several heart rots are also named.

For who takes reports of regulated pests, see reporting a pest in the United States, and pests and diseases by country sets out which ones agencies regulate. A separate page covers the Cytospora canker of spruce.

Use as an ornamental

The handbook calls blue spruce valued mainly for its appearance, because of its symmetrical pyramidal form and the glaucous bluish or silvery-gray foliage that some trees show. It says the wax on the needle surface causes the color, which seems to intensify with age, and that these traits are only occasionally found in natural stands. Silvics reports at least 38 named cultivars based on leaf color and crown form, introduction to Europe late in the 19th century, and use as a Christmas tree in plantations inside and outside its native range. It adds that the branches begin to droop and the crown thins and becomes irregular as the tree ages, and it calls the wood brittle and often full of knots, so blue spruce is not an important timber tree. The handbook says foliage color varies under strong genetic control and is a characteristic to expect with seed-produced trees.