Western juniper (Juniperus occidentalis) is a native North American conifer with wide natural distribution in the mountainous areas of Oregon, Washington, Northern California, and Nevada. Western junipers grow to an average of 50 feet tall, with exceptional trees growing to heights as tall as 80 feet. Juvenile plants have needle-like leaves about 1/4-inch long, which gradually become scale-like structures as the plant matures. Often mistaken for berries, the small cones have a fleshy blue pulp often covered in white.
Western juniper is a very slow-growing tree that is somewhat unusual in the nursery trade—perhaps because it is very widespread as a native specimen and is sometimes considered weedy and invasive. As a landscape tree, it is usually planted as a container-grown or ball-and-burlap tree in the spring or fall. It can take as much as 100 years to reach its full 50-foot height, and a seedling may achieve only about 10 feet in its first 20 years.
|Common Name||Western juniper|
|Botanical Name||Juniperus occidentalis|
|Plant Type||Coniferous shrub, tree|
|Mature Size||12–50 ft. tall, 10–40 ft. wide|
|Sun Exposure||Full to partial|
|Soil Type||Dry to medium moisture, rocky|
|Soil pH||Slightly acidic to slightly alkaline (6.0 to 8.0)|
|Bloom Time||Cones/berries mature in fall|
|Flower Color||Blue/purple berries have white coating|
|Hardiness Zones||5-9 (USDA)|
|Native Range||West to Pacific Northwest United States|
Western Juniper Care
There are several hurdles to clean when growing a western juniper. First, it can be difficult species to find in garden centers, as it has developed a growing reputation as a weedy, invasive plant, and some nurseries are shying away from stocking it.
Second, western juniper is an extremely slow-growing tree with an evolving growth habit, requiring that you give careful long-term planning before choosing it. For the first 10 years or so, the tree’s growth will mostly be in the form of sending a tap root downward. Next, it will send out lateral roots along the surface that may be five times the height of the young tree. Finally, at about 15 years of age, the tree will get a growth spurt and start rapidly growing up, as much as 6 inches a year, to begin creating its final conical form. The western juniper is truly an exercise in patience. Thus, a western juniper may display as a rather low, shrubby plant for several decades before beginning its upward growth spurt and becoming a stately upright tree in its old age.
With those considerations in mind, consider your location and plan the home of your western juniper. It will be calling its space home for a very long time. Think about utilities and infrastructure that roots may need to contend with, not just now, but up to two decades in the future.
To plant, remove the tree from its burlap or container (unless you have gotten bareroot) and set it into a hole twice as wide as your tree’s root ball, or container, and just as deep. Make sure to keep it in an upright position as you fill the hole and compress the soil. Lightly mulch over the root zone to a depth of 3 inches, right out to the edges of the tree's dripline, 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.
As humans spread and develop housing, ranching, or commercial properties into areas that were once prime ecosystems for the western juniper, the tree has spread elsewhere. This has made the once-great tree somewhat of a nuisance in places that call for forest management. If you live in such an area, consult local experts on the advisability of planting this species.
The western juniper prefers full sun but will handle part shade. Like all junipers, it is adaptable but it will not thrive in a full-shade location.
Western juniper is perfectly suited for loose, rocky soil, though it adapts well to more fertile soil. Like most conifers, it prefers a slightly acidic soil condition, but this species has evolved to do quite well in slightly alkaline soil with pH up to 8.0. Adding vermiculite, perlite or a pumice mixture is perfect if you are looking to amend your soil to give it texture to help your juniper thrive. In more favorable soil, it may more quickly assume the upright mature growth pattern that can take many decades when growing in rockier soils.
Once mature, a western juniper will find water with its immense root system, but it will require more frequent watering when young. It is a drought-tolerant species, as are most plants in the genus Juniperus.
Temperature and Humidity
In its native range, western juniper is found the areas of USDA zones 5 to 9 where the summers are hot and dry and the winters are cool to cold. Gardeners in the southern end of zone 4 can sometimes grow it successfully. It is most prevalent in areas with low relative humidity. But this is an adaptable plant that is hardy at temperatures down to minus 20 degrees Fahrenheit.
The western juniper does not require feeding. It prefers rocky, fairly barren soil and may develop an uncharacteristic growth habit if it is fertilized.
Types of Western Juniper
There are no named cultivars commonly sold in the commercial trade, but western juniper is found in two naturally occurring variations:
- Juniperus occidentalis var. occidentalis is the most common variation—the one most often offered for sale in the trade.
- Juniperus occidentalis var. australis is more commonly known as Sierra juniper. It has a more southern range than western juniper and features a very thick trunk with sinewy reddish-brown bark.
Junipers are typically allowed to assume a fairly natural, irregular or windswept shape, pruned only to remove dead or diseased limbs rather than to strictly control the plant's shape. Like most junipers, western juniper is best pruned in late winter or very early spring before new growth starts. It's generally better to perform small, regular pruning sessions rather than allow the plant to become badly overgrown—it doesn't much care for major pruning.
When branch tips must be pruned, cut them back only to a point where green growth is still present. The standard method is to make these pruning cuts on the bottom side of the branches, where the cut edges will be hidden by greenery. If you cut back to non-green growth, it can take many years for these cuts to be concealed.
Propagating Western Juniper
Seed propagation is quite time-consuming and difficult for these plants, so the most common commercial method is through stem cuttings. This is not a particularly easy method, ether, as it can take a full year for the cuttings to root and mature into plants that can be transplanted outdoors. But if you want to try it, here's a method:
- In early summer, use sharp pruners to clip an 8- to 10-inch stem with plenty of needles. Remove the needles from the bottom 2 inches, then make 1- to 2-inch slits on each side of the stem, using a sharp knife
- After dipping the cut end in rooting hormone, plant the cutting in a pot filled with standard peat-based potting mix blended with an equal amount of sand. Thoroughly moisten the potting medium.
- Place the pot in a large, loosely secured plastic bag to hold in moisture. Place the pot in a location with bright indirect light, at a temperature of 60 to 65 degrees Fahrenheit. Begin checking for roots after about four weeks, You'll know roots have formed when you feel resistance when tugging lightly on the stem of the cutting.
- Once roots have developed, remove the plastic bag and continue growing the cutting in a sunny location for a full growing season. If the plant has rooted and is actively growing by mid-summer, it may be ready to plant by late fall of the same year. More likely, though, you'll need to overwinter it in a sheltered location and allowed it to grow for another year before planting the following fall.
Success is not a certainty when it comes to propagating junipers through cuttings, so it's best to start several to ensure that at least one cutting succeeds.
How to Grow Western Juniper From Seed
Western junipers do not begin producing seeds until they are at least 20 years old, and the seeds require repeated cycles of cold-moist stratification until the hard seed coats break down and the seeds germinate. This is not a method most homeowners want to try, as germination can take as much as three years.
Forestry service analysis shows that seed germination and successful seedling development almost always occur in conditions of light shade. Serious amateurs wishing to experiment with seed propagation can try planting seeds from the blue berry/cones of a mature tree in small pots filled with a rocky/sandy growing medium and setting the pots in a sheltered, lightly shaded position for several years.
Potting and Repotting Western Juniper
Western juniper is rarely used for container culture, with one major exception: It is often used in the art of bonsai. Once again, an issue is finding a specimen in the nursery trade. A solution is finding seedlings on private land that you have gained permission to use. The young seedlings are still at a point that can be transplanted. But always remember to get the permission of the landowner and never take from public land. Plant poaching is illegal and could get you into serious trouble.
Once you find a specimen you like, transplant it to a pot with bonsai soil, which consists of inorganics such as pumice, vermiculite, and crushed lava. Occasionally, pine bark is also included. After some time, you can repot to a larger container by removing the soil from the roots and trimming then shaping the tree into your very own western juniper bonsai. Containers can be any material you like, though bonsai plants tend to look best in ornamental ceramic or clay pots that are wide and relatively shallow. As with any potted plant, the container should have at least one, and preferably several drainage holes.
When growing within its accepted hardiness range, western juniper requires no winter protection against cold. In very windy locations, it may be helpful to stake a young plant to keep it upward. However, a wind-swept look can also be desirable, so some homeowners deliberately position western junipers where they will experience strong winds.
Common Pests and Plant Diseases
As befits a native species with a reputation for ready spread, western juniper is not affected by any serious pest or disease issues. Juniper bark beetles (Phloeosinus serratus) can kill trees that are weakened by severe drought. Gall midges feed on western juniper and produce woody galls, but the problem is rarely serious. Fungal diseases such as white trunk rot (Pyrofomes demidoffii) are possible where the trees are growing in overly moist conditions but rarely occur if the tree is growing in properly dry, rocky soil.
How to Get Western Juniper to Bloom
While attractive flowers aren't a feature of this tree, homeowners sometimes lament the absence of the blue-whitish cones (berries) that they expect to see on a juniper tree. This absence is usually just a matter of maturity, as it takes a western juniper a full 20 years to mature into a berry-producing tree.
Common Problems With Western Juniper
There are no serious cultural problems with western juniper, but growers are sometimes puzzled and alarmed by the appearance of strange, twiggy balls that appear in the branches of the tree. These balls are sometimes large and heavy enough to break limbs.
These balls are actually parasitic mistletoe plants. Western junipers are a common host to two such species of mistletoe. The balls generally don't do serious injury to otherwise healthy junipers, but you can systematically cut them out of the tree if you don't like the look. Some people, however, leave mistletoe alone for the benefit of cuttings they can take for use in holiday displays.
How can I use this plant in the landscape?
The size and shape of this plant will change radically as it matures, so keep this in mind when you plant it. In the early years, western juniper often has a low, ground-hugging, shrubby appearance that can work well in large rock gardens or other barren areas. But if planted in deeper, richer soil, it will eventually become a rather large upright tree, though it can take many decades for this transformation.
Western juniper is not always an ideal landscape tree, but it can be a good addition to scrubby, naturalized areas, such as rocky slopes or dry meadows.
How long does a western juniper live?
No one know exactly, though there are specimens believed to be over 3,000 years old (the Bennet juniper in the Stanislaus National Forest of California). Trees that are centuries old are relatively common. Suffice it to say that these trees will last a long, long time if you plan and care for them properly. It's not unlikely that the tree will outlive you, your children, and even your grandchildren.
Is there any way to make western juniper grow faster?
Not really. These plants have a natural affinity for rocky, poor soils, and if planted in fertile, deep soil, they sometimes grow a bit faster. And plenty of water may slightly increase the growth rate, though this also increases the danger of fungal diseases. It's best to carefully consider the slow growth rate of these plants, and include it in your landscape only if its slow performance and gradual evolution make sense for your landscape design.
What about fire danger?
Like most conifers, western juniper is a resinous tree that burns very well. In fact, fire is by far the leading cause of mortality for this species. Do not plant these trees in areas where wildfire is a common threat, and take precautions to keep them well separated from buildings.
Does western juniper have wildlife value?
Yes, this tree's berries serve as a food source for many browsing animals, such as deer, elk, chipmunks, squirrels, turkeys, and songbirds.