Colorado Blue Spruce bonsai

Colorado Blue Spruce Bonsai Care

Picea pungens

Zones 2 to 7, outdoor only. Native to the Rocky Mountains of the United States, from Montana and Idaho south to Arizona and New Mexico.

Pinaceae (the pine family) · Evergreen conifer

At a glance

Type
Conifer
Leaves
Evergreen
USDA zones
2 to 7
Indoor or outdoor
Outdoor
Growth rate
Slow
Styles suited
Windswept
Bonsai popularity
Tier 1

Close-up photo reference

Compare your tree against these to confirm the species and spot problems early.

Close view of Colorado Blue Spruce needles
Foliage / leaf detail, JustTooLazy · CC BY 2.0
Colorado Blue Spruce cones
Cone, JJ Harrison (https://www.jjharrison.com.au/) · CC BY-SA 3.0

Colorado Blue Spruce quick reference

USDA zones2 to 7 in the ground [2]; UF/IFAS gives 4 to 7 [3] and Purdue zone 3 [4]; no source gives a zone for a pot
Indoor / outdoorOutdoor only: spruce bonsai stay outside all year [13]
LightFull sun [13] [14]; Bonsai Mirai also allows partial shade, with afternoon shade in extreme heat [12]
WaterSources differ: Bonsai Mirai keeps the soil evenly watered and never waterlogged [12]; Bjorholm waters as the surface dries and keeps it slightly drier [14]; Bonsai Empire waters thoroughly as soon as the soil dries [13]
SoilFree-draining mix of akadama, pumice and lava rock [12] [14]
RepotEvery 2 to 4 years [12] [13]; Bonsai Mirai's FAQ says 3 to 5 [12]; very old trees can wait longer [13]
FrostHardy to zone 2 in the ground [2]; in a pot, Bonsai Mirai shelters it below 20°F (about -7°C) [12] and Bonsai Empire advises frost protection [13]
Mature height30 to 60 ft (9 to 18 m) in the landscape [2], up to 70 to 115 ft (21 to 35 m) in the wild [5]; no source gives a bonsai size
Growth rateSlow in the ground [3] [5]; NC State says slow to medium [2]; not rated as a bonsai
Season of interestSilvery blue needles [2] all year; hanging cones 2 to 4 in long [2]
Leaf reductionNot rated by the sources we checked
Main risksMain risks, not ranked by any source: waterlogged or dried-out roots [12] [13]; cutting back into bare old wood [13] [16]; needle cast and canker [9] [11]

Overview & Character

Colorado blue spruce is native to the Rocky Mountains of the United States, from Montana and Idaho south to Arizona and New Mexico [1]. Kew accepts the name Picea pungens [1]. It grows wild in cool mountain climates [5], on moist sites such as streambanks and ravines, since its roots are shallow [5]. The species name refers to its stiff, sharp foliage [8], and most of the strongly blue forms are produced by grafting [4], since seedlings vary in color [3]; at least 38 named cultivars exist [8]. Bonsai Empire calls it a popular bonsai species in the US [13].

This is a hard tree to work. Bonsai4Me says spruce are difficult to style as bonsai [15]. Bonsai Empire says spruce will not backbud from old wood [13], and Bonsai4Me says backbudding can be encouraged but stays limited [16]. Plan every branch around foliage you already have.

Identification

Foliage. Single, four-sided, stiff, sharply pointed needles [4] [6], silvery blue [2] to blue-green [8]. Length is about 1 in [6], up to 1 in [2]; the Gymnosperm Database gives 0.6 to 1.2 in (1.6 to 3 cm) [8]. Each needle sits on a short stalk that stays on the twig, so a bare twig feels rough [6].

Bark & trunk. Purplish-gray, deeply grooved and thickly scaled [2]; light to dark gray thin scales that form wide, thick ridges on older trees [6].

Cones. Papery, hanging, light chestnut-brown [6], 2.5 to 4 in (6.4 to 10.2 cm) long with thin, flexible scales [5].

Look-alikes & how to tell them apart: The Gymnosperm Database notes limited hybridization with Engelmann spruce [8], but none of the sources we checked gives a key between the two. Blue spruce twigs are usually hairless [6] [8].

Climate & USDA Zone

Figures for trees in the ground: zones 2a to 7a (NC State) [2], 4A to 7B (UF/IFAS) [3], zone 3 (Purdue, blue form) [4]; RHS hardiness H7, below -4°F (-20°C) [7]. It prefers cool climates and suffers in heat and humidity [2].

In a pot the roots are more exposed. Bonsai Empire wants a winter dormancy below about 45°F (7°C), with frost protection in a bonsai pot and a cold frame or unheated garage in very cold climates [13]. Bonsai Mirai shelters it below 20°F (about -7°C) [12]. Bonsai4Me rates spruce in general hardy to 14°F (-10°C) [15].

Light

Full sun in the growing season [13]; it can take direct sun all year [14]. In hot climates give shade in the hottest months [14]: afternoon shade (Bonsai Mirai) [12] or midday shade (Bonsai4Me) [15]. Bonsai Empire moves it to semi-shade in winter [13].

Watering

Sources differ. Bonsai Mirai keeps the soil consistently moist but not waterlogged [12]. Bjorholm says these spruce do better kept slightly drier, watering as the surface dries [14]. Bonsai Empire waters thoroughly as soon as the soil gets dry, without keeping the roots soaking [13].

In the growing season most trees need water once a day, sometimes twice [14]. In winter, cut back on water, but do not let the root ball dry out fully [13]; that can mean once every 3 to 5 days [14].

Soil & Root Care

Use a free-draining mix of akadama, pumice and lava rock [12], 1:1:1 for Bjorholm [14].

Repotting timing differs. Bonsai Mirai and Bjorholm repot in early spring, around bud swell [12] [14]; Bonsai4Me repots spruce in late summer or early fall [15]. Repot every 2 to 4 years [12] [13] (3 to 5 in Bonsai Mirai's FAQ [12]); very old trees can wait longer [13].

Cut roots lightly: old spruce will not tolerate losing larger roots [13], and heavy root loss can weaken the tree the next season [14].

Feeding

Schedules differ. Bonsai Mirai uses a balanced slow-release fertilizer every 4 to 6 weeks, early spring to late summer [12]. Bonsai Empire uses solid organic fertilizer every four weeks or liquid every week in the growing season [13]. Bonsai4Me feeds every two weeks [15]. Bjorholm gives young trees a high-nitrogen synthetic feed and refined trees a milder organic one, through late fall [14].

Pruning & Styling

Keep foliage on every branch you keep. Spruce will not backbud from old wood [13]. Bonsai4Me says not to rely on buds on old branches unless the tree has been very heavily cut back, and a shoot cut back with no bud left may die [16]. Shorten long branches to smaller twigs near the trunk [13], and in the lower half keep one branch per whorl [13].

Shoot work in spring. These species usually make one flush a year [14]. Bjorholm lets new shoots reach 0.5 to 1.5 in, then pinches or cuts each back to an even length; back buds are then likely lower on the shoot [14]. Bonsai Empire pinches while shoots are still soft [13]. Bonsai4Me pinches at about 0.8 to 1.2 in (2 to 3 cm) [15], or cuts 1 to 2 in shoots by a third on strong tops and by half or less on weak ones [16].

Bonsai4Me makes hard cuts only in fall [15]; Bonsai Mirai does structural pruning in early spring [12] and avoids heavy pruning in late summer or fall [12].

Wiring timing differs. Late winter or early spring (Bonsai Mirai) [12]; late summer or early spring, never midsummer (Bonsai Empire) [13]; fall or late winter (Bjorholm) [14]; fall and winter only (Bonsai4Me) [15]. Mature branches can take years to set [16].

Styles. Bonsai Mirai suggests windswept or classic upright [12]. Bonsai4Me finds upright spruce very difficult to style realistically without suitable raw material [16] and rules out only broom [15].

Seasonal Calendar

Care calendar by month

Northern Hemisphere. In the Southern Hemisphere, shift every month by six.

Propagation & Cuttings

Ease: Not rated by the sources we checked. Best methods: seed and cuttings [13]; root cutting and seed [2]; grafting for reliably blue trees [3] [4].

Seed needs cold stratification [12]; Bonsai4Me sows outside in spring [15]. Seedlings vary in color, so UF/IFAS recommends grafted cultivars for a reliable blue [3]. Take cuttings in late summer [13], with rooting hormone [12]; they can take a very long time to strike [15].

Pests

Spruce spider mite [2] [13] [14]. Mites can be a serious problem in summer after hot, dry weather [3]. Also aphids, scale, budworms and bagworms [2], gall adelgids [4] [13], spruce needle miners [3] [13] and bark beetles [14]. Bonsai Mirai relies on regular inspection and good air circulation [12].

Disease, Fungus & Infection

Rhizosphaera needle cast. Colorado blue spruce is among the worst affected spruces [9]. Needles on lower interior branches turn purple, then brown, and the disease climbs the tree year by year [9]. Long needle wetness and shade favor it [9]. UMass prunes out declining lower branches and sprays in spring when new growth is 1/2 in long [9].

Stigmina needle cast. Easily confused with Rhizosphaera; it sheds one-year-old needles on lower branches, and drought stress predisposes trees to it [10].

Cytospora canker. Sunken, resin-oozing cankers on lower branches, which develop on drought-stressed trees; prune them out, disinfecting tools between cuts [11].

In a pot, Bonsai Mirai warns that fungal disease may follow overly moist conditions [12].

Most Common Causes of Death

No source we checked ranks these. They are the main risks the sources describe, in no particular order:

Toxicity, Safety & Handling

The needles are stiff and sharply pointed [4] [6]. NC State notes that the dangerous leaf tips have injured toddlers [2]. Handle it with care when pinching and wiring.

Sources

  1. Kew Plants of the World Online: Picea pungens
  2. NC State Extension Plant Toolbox: Picea pungens
  3. UF/IFAS EDIS: Picea pungens, Colorado Spruce
  4. Purdue Arboretum Explorer: Picea pungens f. glauca, Colorado Blue Spruce
  5. USDA Forest Service Fire Effects Information System: Picea pungens
  6. Utah State University Extension Forestry: Blue or Colorado Spruce
  7. RHS Plants: Picea pungens
  8. The Gymnosperm Database: Picea pungens
  9. UMass Amherst Extension: Rhizosphaera needle cast
  10. UMass Amherst Extension: Stigmina needle cast
  11. Penn State Extension: Cytospora canker on spruce
  12. Bonsai Mirai: Blue Spruce bonsai
  13. Bonsai Empire: Spruce bonsai care
  14. Bjorn Bjorholm: Care and maintenance guide for native US spruce and fir bonsai
  15. Bonsai4Me: Picea / Spruce bonsai
  16. Bonsai4Me: Picea / Spruce bonsai, styling, pruning and wiring

Where to buy a Colorado Blue Spruce bonsai

We don’t stock Colorado Blue Spruce at the moment. These species need similar care and we have them now, they are the closest match in our catalogue.

Browse all bonsai trees for sale or find a species matched to your climate and space.

Built by Innovation Nexus