Rocky Mountain Juniper (Juniperus scopulorum) is a slow-growing evergreen tree valued for its versatility and beauty. This hardy tree typically reaches heights of 5 to 6 meters and features a columnar to rounded shape, making it a striking addition to gardens and landscapes. Its dense, dark green foliage provides year-round interest, while its berries attract birds and other wildlife, enhancing biodiversity in your outdoor space.
Native to western Canada, the western United States, and northern Mexico, Rocky Mountain Juniper thrives in dry, well-drained soils and is well-suited for arid and semi-arid regions. Its aromatic wood, prized for its durability and pleasant scent, is commonly used in cedar chests and lumber products. However, this tree does not perform well in humid climates, so it is best suited for areas with low to moderate humidity.
| Common name | Colorado Red Cedar, Mountain Red Cedar, River Juniper, Rocky Mountain Juniper, Rocky Mountain Red Cedar |
| Botanical name | Juniperus scopulorum |
| Family | Cupressaceae |
| Species | scopulorum |
| Origin | Western Canada, western USA to Northern Mexico |
| Life cycle | Woody |
| Plant type | Tree |
| Hardiness zone | 3, 4, 5, 6, 7 |
| Sunlight | Full Sun |
| Maintenance | Low |
| Soil condition | Clay |
| Drainage | Well-Drained |
| Growth rate | Slow |
| Spacing | 12 – 24 ft. |
| Harvest time | Fall |
| Flowering period | Spring |
| Height | 3- 40 ft. |
| Flower color | Gold, Yellow |
| Leaf color | Blue |
| Fruit color | Blue |
| Fruit type | Berry |
| Leaf benefit | Fragrant |
| Uses | Lawn |
I. Appearance and Characteristics
Juniperus scopulorum, the Rocky Mountain juniper, is a species of juniper native to western North America, from southwest Canada to the Great Plains of the United States and small areas of northern Mexico. They are the most widespread of all the New World junipers.
Juniperus scopulorum is a small evergreen tree that in favorable conditions may reach as much 20 metres (66 feet) in height. However, on sites with little water or intense sun it will only be a shrub and even when growing into a tree form it will more typically be 4.6–6.1 metres (15–20 feet) tall in open juniper woodlands. When younger trees will have narrow pyramidal shape, but develop into a rounded, oval, or spreading and irregular crown when older.
They may either have a single trunk or multiple stems. Trunks can be large on mature trees, 38–76 centimetres (15–30 inches) in diameter. When the subsoil is difficult to penetrate and lacks moisure the roots of Juniperus scopulorum spread out. They are numerous and fibrous in the upper part of the soil. When soils are deep and well drained they will grow to a greater depth.
On twigs between 5 and 10 millimetres (3⁄16 and 13⁄32 in) in diameter the bark is smooth. On larger twigs and branches it becomes rough, coming off in thin strips. Juniperus scopulorum has red-brown bark on branches that can weather to grey on the trunk. The texture of the bark is rough and comes away in shreds on the trunk with brown bark showing in the cracks at times. Branches tend to grow outwards a short distance and then curve to growing upwards (ascending). In sheltered to somewhat shady locations the branches may hang downwards and be quite slender. The very ends, the branchlets, can either stand upright or hang down.
Young shoots are very slender. All the leaves are light to dark green, but are often covered in a waxy coating that gives a blue or white cast to the leaves (glaucous) making them appear blue-gray or blue. On immature trees they will be covered in sharp needle like “whip leaves” 3–6 millimetres (1⁄8–1⁄4 in) long that stick out from the shoots. The needles will not have the waxy coating on their upper surface. What appear to be green scales on the shoots of adult trees are the mature leaves which clasp the shoot in opposite pairs with the next pair down or up the shoot rotated a quarter turn (90°) around it (decussate). Occasionally they will be turned one third to make the shoot three sided. The scales either do not overlap or overlap for at most one-fifth of their length of 1–3 millimetres (1⁄32–1⁄8 in).
The seed cones are berry-like that are round to somewhat irregular in shape with two lobes (globose to bilobed) and 5–9 mm (3⁄16–11⁄32 in) in diameter. They are dark blue-black in color, but will be pale blue-white when covered in natural wax. The berries most often contain two seeds, but may contain one or three; they are mature in about 18 months. The pollen cones are 2–4 mm (3⁄32–5⁄32 in) long, and shed their pollen in early spring, generally in April. It is usually dioecious, producing cones of only one sex on each tree, but is occasionally monoecious.
Chemistry
Rocky Mountain juniper is an aromatic plant. Essential oil extracted from the trunk is prominent in cis-thujopsene, α-pinene, cedrol, allo-aromadendrene epoxide, (E)-caryophyllene, and widdrol. Limb essential oil is primarily α-pinene and leaf essential oil is primarily sabinene. Experiments with deer have found that oxygenated monoterpenes, like sabinene, inhibit the gut bacteria of ruminants and deer show the expected preference for foliage lower in these chemicals.
Similar species
Juniperus scopulorum is closely related to eastern redcedar (Juniperus virginiana), and often hybridizes with it where their ranges meet on the Great Plains. It will also form hybrids with alligator juniper (Juniperus deppeana), creeping juniper (Juniperus horizontalis), oneseed juniper (Juniperus monosperma), and Utah juniper (Juniperus osteosperma). The population of juniper trees in Mexico near the former site of Colonia Pacheco, Chihuahua is a hybrid with Juniperus blancoi. There is some disagreement whether hybrids are formed with the oneseed juniper in the wild.
II. How to Grow and Care
Sunlight
The Rocky Mountain juniper prefers full sun but will take partial shade. Like all junipers, it is pretty adaptable.
Temperature and Humidity
This plant prefers warm dry temperatures, but it is cold hardy to -35 degrees Fahrenheit.
Watering
Rocky mountain juniper does not tolerate soggy roots. Water rocky mountain juniper when the top 2.5 to 5 cm of soil dries out for the first two years until it has been established. After that, it will be content with casual rainfall. Potted plants require more water, but ensure there is good drainage so the roots are not sitting in water. Water only when the top 2.5 to 5 cm of soil dries out in your pot, so ensure good drainage for potted plants.
Soil
The ideal soil for this tree is a loose, inorganic mix of a neutral pH. Adding vermiculite, perlite or a pumice mixture is perfect if you are looking to amend your soil to give it texture.
Fertilizing
Rocky mountain juniper can benefit from an annual feed of slow-release organic or all-purpose fertilizer. This should be done in early spring as it gives your rocky mountain juniper time to grow and prepare for winter dormancy. Although you can use chemical fertilizers, it’s not recommended due to the plant’s sensitive roots.
Planting Instructions
To plant your tree, pick your location knowing the size, and the characteristics of your tree. Consider the utilities and any infrastructure under the plant and think about future improvements.
Once a site is chosen, dig a hole twice as wide as your tree’s root ball, or container, and just as deep. Remove the tree from the container or burlap and set it in the hole. Maintain it in an upright position as you fill the hole and compress the soil. Lightly mulch to a depth of 3 inches to the dripline of the tree making sure that no mulch touches the trunk of the tree itself.
If your tree is in a windy spot, consider staking it to ensure that it remains upright.
Pruning
Rocky Mountain juniper should be pruned around a central leader, a hardy stem that grows upright. Prune it in early spring, after the last chance of frost has passed but before new buds set on the stems. Cut any dead, damaged, or diseased stems down to the trunk. Cut out tips of branches if it might open up the tree and allow light to touch more branches in the center. In total, try to cut back only 20 percent of the tree each season.
Propagation
Juniper can be propagated via cuttings, seed, or grafting. Grafting is rather difficult and requires an experienced gardener to make it work well. Therefore, creating a cutting for propagation, or using seeds, will be the most common routes for the typical home gardener. Here’s how to propagate Rocky Mountain juniper using cuttings:
- To create the proper cutting, choose a branch that is healthy and green. Do this during the winter or early spring, as you want to use only established growth.
- Separate the cutting from the main branch with sharp shears, so that you have a “heel” or “node” on one side and lively growth on the other.
- Peel the bottom half of the cutting, up to about 1 inch, then dip it in rooting hormone. Place this in damp peat moss and tamp the medium down thoroughly.
- Use pots that are at least 5 inches deep to allow for better root growth. It might take up to six months for the cuttings to develop their root systems.
How to Grow From Seed
It’s possible to grow Rocky Mountain juniper from seed. Here’s how:
- Collect seeds in the fall, clean them well, and place them in a paper bag. Keep this bag in a cool place, such as a garage, through the winter.
- In early spring, sow the seeds in 5-inch pots, with about 1 inch between each seed. Cover them lightly with potting soil and water thoroughly.
- Though a greenhouse is best for growing these tiny saplings, a transparent lid can help raise the humidity enough if the pots are in sunlight. Look for temperatures above 75 degrees Fahrenheit and humidity at above 75 percent.
- Expect the first shoots to appear within two weeks.
Potting and Repotting
Rocky Mountain juniper can’t be grown in pots unless it is a variety specifically meant for bonsai enthusiasts. Allow other varieties to grow in a pot only until ready to plant outdoors.
Overwintering
These trees thrive even in very low temperatures. Young, immature trees might benefit from mulch over the roots if the temperatures dip below 10 degrees Fahrenheit. Adult trees are cold hardy and don’t need protection through the winter.
Pests and Diseases
Spider mites and bagworms are common pests that make their home in the Rocky Mountain juniper. Botanical oils and insecticidal soaps can help with the problem. Bagworms can be removed by hand and killed by dropping into a bucket of warm, soapy water.
Rocky Mountain juniper is vulnerable to Cercospera blight; copper-based fungicides can help with this issue. The tree might also develop Botryospaeria stevensii canker, especially when growing in humid areas. Cutting out the affected area is usually the best and easiest solution. Keep in mind that canker usually takes hold only if the tree is already stressed, so pay closer attention to proper watering, pruning, and soil amendments.
III. Uses and Benefits
- Ornamental uses
Rocky mountain juniper is a long-lived but slow-growing small tree or shrub often cultivated as a wind block, street tree, or visual screen. They are particularly pleasing when male and female trees are planted near each other, as they will produce small flowers and attractive juniper berry fruits. The roots are shallow, and some appear at the ground’s surface: an important consideration when choosing a location to plant this tree.
- Wood
The wood of Rocky Mountain Juniper is quite rot-resistant when cured, and prior to the widespread adoption of the steel fence post they were often harvested to build fences in the American west. The wood is lighter in weight and not as hard as that of the Eastern red cedar. In strength, color, and appearance it is difficult to distinguish the two apart. The outer sapwood is light-colored while the inner heartwood is deep red with occasional streaks of white or purple. Due to the usually small size of their trunks they are not much utilized as timber except for making specialty products like “cedar” linings for closets or chests to repel moths. As a fuel wood it is only of fair quality. It has an excellent smell when burning, but produces poor coals, lots of sparks, and is moderately difficult to split.
- Traditional uses
Some Plateau Indian tribes boiled an infusion from the leaves and inner bark to treat coughs and fevers. The cones were also sometimes boiled into a drink used as a laxative and to treat colds. Among many Native American cultures, the smoke of the burning juniper is used to drive away evil spirits prior to conducting a ceremony, such as a healing ceremony.
A small quantity of ripe berries can be eaten as an emergency food or as a sage-like seasoning for meat. The dried berries can be roasted and ground into a coffee substitute.
IV. Types of Rocky Mountain Juniper
In the United States, the Rocky Mountain juniper is a favorite for the bonsai enthusiast. To create a bonsai using a Rocky Mountain juniper, there are a few dwarf or miniature cultivars available that are perfectly suited for bonsai creations.
- Juniperus scopulorum ‘Snow Flurries’: This is an especially nice, variegated cultivar. You need to transplant it into a pot just large enough for its roots with a premixed bonsai soil that will consist of inorganics such as pumice, vermiculite, and crushed lava. Occasionally, pine bark is also included.
- Juniperus scopulorum ‘Blue Arrow’: If you are looking for a tall slender cultivar for the garden, you might want to choose Juniperusscopulorum ‘Blue Arrow’, this cultivar is often used as windscreens and hedges.
- Juniperus scopulorum ‘Wichita Blue’: This variety has a pyramidal shape and features blue to blue-gray foliage. It’s a male plant that grows slowly, up to 6-12″ per year.
Find Where to Buy the Best Rocky Mountain Juniper (Juniperus scopulorum)
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