Description

• Habit
• Size
• Growth Rate
• Hardiness
• Leaves
• Bark
• Flowers
• Fruit
• Seed
• Roots

Habit: Small-to-medium, coniferous, evergreen shrub or tree; species normally narrow, pyramidal but highly variable (Bridger-Select broadly pyramidal); spreading branches that extend to the ground; usually multi-stemmed. (Figure 1)

Figure 1

Size: Variable; under clean cultivation and dryland conditions east of the Continental Divide, expect a 20-year height and width of approximately 12 and 9 feet, respectively, for adapted ecotypes (20-y height and width of 15+ and 13.5+ ft., respectively, for Bridger-Select); mature height estimated at 15 to 20 feet.

Growth Rate: Slow, less than 6 to 12 inches/year (9 to 11 in./yr. for Bridger-Select) under clean cultivation and dryland conditions east of the Continental Divide; anticipate greater rates of growth for all Rocky Mountain juniper in higher precipitation zones and when supplemental moisture is provided.

Hardiness: USDA Hardiness Zones 3 to 7. (See also Adaptation)

Leaves: Mature leaves scale-like (Figure 2), young plants with a high percentage of needle-like foliage; shape between an egg and a diamond; tip of leaf with sides that are straight to curved and taper to a point; margins without teeth; tops varying in color from dark green or bluish green, with a whitish covering or light green; back of leaves dark or light bluish green, with a whitish covering, or light green with inconspicuous glands, winter color similarly variable ranging from dull green to bluish purple to nearly reddish brown, dark purple to brown winter color often mistakenly diagnosed as symptomatic of stress.

Figure 2

Bark: Reddish-brown, slightly rough, persistent, scaly bark in the sapling and pole stages, becoming increasingly stringy and fibrous with age-usually with multiple stems.

Flowers: Male and female cones (strobili) on separate plants, small and borne on the ends of short branchlets from mid-April to mid-June; female cones are greenish-yellow becoming more conspicuous in late summer and opening the following spring before pollination (Figure 3); pollination primarily by wind; male cones brown. (Figure 4)

Figure 3

Figure 4

Fruit: Berry-like, purplish-blue-black in color at maturity, with a whitish surface covering (Figure 5), 0.2 to 0.3 inches diameter; ripening 2 years after pollination, from mid-September to mid-December, and can remain on the tree until March or April of the following year-fr detailed collection and processing information, reference PM Tech Note No. MT-34: Improved Processing of Rocky Mountain Juniper- contains one, sometimes two, and rarely three seed; production typically begins at 10 years of age under favorable conditions.

Figure 5

Seed: Reddish brown, angular, and lightly to prominently grooved. (Figure 6) A high proportion of unfilled seed is common, but varies widely from tree to tree and season to season. It averages 27,100 seeds per pound, but ranges from 17,800 to 42,100 seeds per pound. One, two, or even three seeds can be found in each fruit. Variation in the number and arrangement of embryos also occurs. A single seed may contain a single embryo or it may contain two embryos in individual chambers separated by a common woody wall. In some cases, two seed, each with an embryo, are lightly fused but can be separated with force to produce two distinct seed. Wildland Rocky Mountain juniper rates as a fair seed producer in Montana-Bridger-Select rates fair to good under cultivation. Heavy crops occur every 2 to 5 years, but some seed is produced almost each year. Wildland seed viability is fair, with an average germination capacity of 22 percent and maximum values seldom exceeding 35 percent. In a cultivated orchard, Bridger-Select Rocky Mountain juniper averages 40 to 50 percent viability, ranging from 8 to 91 percent. When procuring commercial seed, purchase it on a Pure Live Seed (PLS) basis with a current germination test to assure viability. Bulk seed of unknown viability, purity and/or origin is often a poor value. Store seed at 10 to 12 percent moisture content in a sealed container at 20 to 40°F. A 30 percent germination level after 3.5 years in storage has been measured for this species.

Figure 6

Roots: Rocky Mountain juniper has a shallow but extensive lateral root system, but develops a deeper system in bottom lands and deeper soils.

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Last Modified: 11/30/2007