How to Grow and Care for Common Juniper

Native to the cool temperature climates of the northern hemisphere, common junipers (Juniperus communis) have a nearly complete circumpolar distribution—occurring naturally throughout parts of North America, Europe, and Asia. This makes the common juniper one of the most widely distributed shrubs in the world. In cultivation, J. communis has not received quite as much attention as Chinese juniper (J. chinensis), but there are still dozens of common juniper cultivars to choose from. These hardy evergreen conifers, members of the Cupressaceae family, are variable in form depending on the cultivar and conditions where they are growing. The species form is typically a low-spreading shrub no more than about 5 feet tall and up to 13 feet across, but there are cultivars with tall, tree-like form, as well as creeping groundcover forms that grow just a few inches in height. Varieties bred for landscape use are rarely more than 15 feet tall, and many are much smaller. All common junipers are characterized by short needle-like, aromatic leaves and berry-like green cones that turn a deep purple/blue as they ripen. 

Common juniper, like most conifers, is usually planted during mild weather of spring or early fall. The rate of growth varies somewhat by variety, but most are slow-growing shrubs, rarely adding more than about 6 inches per year.

Common Juniper Care

For the most part, common junipers are fairly self-sustaining and do not require much attention. They are extremely hardy shrubs that can adapt to a wide range of growing conditions, including poor soils, dry locations, and even inner-city environments, as common junipers are highly tolerant of urban pollution. For the very best performance, give them moist but well-draining soil and plenty of sun.

The planting technique is typically for container-grown woody landscape plants: Dig a hole about twice as wide as the plant's container or root ball; amend the fill soil with organic material; position the shrub in the center of the hole, at the same height it was growing in its container; then backfill firmly and water thoroughly.

Common junipers do not require heavy pruning but if you need to shape them, they can be lightly pruned in the late winter once the worst of the cold has passed.

Light

Common juniper is a sun-loving evergreen that should receive full sun for the majority of the day. If a common juniper does not receive enough light you may notice stalled or stunted growth. Common junipers cannot survive in full shade conditions. 

Soil

When it comes to soil, common junipers are not picky as long as the medium provides good drainage. They are highly adaptable to a wide range of soil conditions and they are not particular about soil pH—preferring a range from mildly acidic to mildly alkaline (4.0 to 8.0), but also growing adequately in highly acidic and highly alkaline soils. Common junipers are also known to grow easily on a wide range of different sites including exposed slopes and plateaus; wooded hillsides; sand terraces and dunes; maritime escarpments; and dry, open, and rocky environments. This doesn't mean you should seek out bad conditions for these shrubs, as they will certainly perform well in a rich, fertile, well-draining soil. But common juniper is a decidedly more tolerant plant than Chinese juniper when it comes to soil conditions.

Water

Common junipers are considered to be drought-tolerant shrubs but are adaptable to both dry and wet conditions. However, they cannot withstand being waterlogged or sitting in standing water, so appropriate drainage is imperative for the common juniper. When grown in their native range, common junipers do not require any supplemental watering. 

Temperature and Humidity

Common junipers are native to the cool temperate climates of the Northern Hemisphere, and as such are tolerant of a wide range of temperatures. Considered hardy in USDA zones 2 to 7, most varieties of common juniper can withstand winter temperatures as low as minus 49 degrees Fahrenheit. Common junipers are less fond of very hot climates south of zone 7, where Chinese junipers are a better choice.

Fertilizer

These hardy shrubs are considered light feeders and do not require regular fertilization. If desired, established common junipers can benefit from a yearly feeding in the late winter to early spring with a slow-release shrub and tree fertilizer, but this is by no means necessary.

Types of Common Juniper

As a landscape plant, the common juniper is sometimes considered inferior to Chinese juniper, of appeal mostly to native plant enthusiasts. This reputation has slowly changed, thanks to the extremely tolerant nature of this plant. While its available cultivars are still less plentiful than those of Chinese juniper, there are several excellent varieties of common juniper to consider:

• Juniperis communis 'Gold Cone' is a 3- to 5-foot-tall shrub with a columnar form and light greenish leaves.
• Juniperis communis 'Repanda' is a prostrate groundcover form, growing 1 to 2 feet tall and 8 to 9 feet wide.
• Juniperis communis ' Compressa' is an upright, cone-shaped shrub growing just 2 to 3 feet tall.
• Juniperis communis 'Hibernica' is a lovely pillar-shaped shrub growing to 15 feet tall.
• Juniperis communis 'Blue Stripe' is a 2-foot tall, 6-feet-wide prostate form with leaves that have a distinctive blue stripe.

There is also an important variation, Juniperis communis var. depressa, which has several named cultivars, including 'Blueberry Delight' and 'Copper Delight'. The depressa variation occurs naturally in the Eastern U.S., growing about 3 to 4 feet tall and up to 12 feet wide. It is used mostly as a ground-cover plant for large areas.

Pruning

Pruning is rarely needed for junipers, other than to remove broken or diseased branches. If you do want to prune it for shape, it is best done in late winter after the worst sub-zero weather has passed. The best method: cut individual branches back to an upward-growing side branch. This method of pruning is time-consuming, but keeps the plant looking young and natural, and is much better than indiscriminate shearing.

Propagating Common Juniper

Propagating junipers by rooting branch cuttings is a dependable method, though you should be aware that many upright varieties are grafted trees. Propagating a branch from such a variety could produce an offspring that looks much different than the parent. But most varieties are rather easily propagated using this method:

1. In late summer, take 4- to 6-inch cuttings from the tips of branches. Ideally, the snipped ends of the cuttings should have a tinge of brown wood.
2. Strip off the needles from the bottom half of the cutting, then dip it in rooting hormone.
3. Plant the cutting in a pot filled with porous potting medium, such as sand or perlite mixed with a commercial potting mix.
4. Place the potted cuttings in a sheltered, relatively warm location and keep them moist until they develop roots; this can require anywhere from six to 12 weeks. In cold winter regions, move the potted cutting into a sheltered location (a cold frame is ideal) to spend the winter months.
5. Allow the rooted cutting to continue growing in containers for a full year. By the following fall, the slow-growing plants should be ready for landscape planting.

How to Grow Common Juniper From Seed

Though it can be a slow process taking up to three years, common junipers are not difficult to grow from seeds. Common junipers are dioecious, meaning that individual trees are either male or female, and must be planted nearby the opposite sex in order to cross-pollinate and produce fruit. Once the fruit of the common juniper has ripened (turned from green to purple-black), the seeds can be harvested and either sown directly into the garden or stored over the winter to be sown in the spring.

If you are not sowing the seeds immediately, they should be cleaned and air-dried to prevent the formation of mold. Common juniper seeds require stratification in order to germinate and must be kept in an airtight container at 20 to 40 degrees Fahrenheit for up to 120 days prior to planting. Because common juniper germination rates are notoriously poor, it's a good idea to sow several seeds at once for the best chances of success.

Seedlings will grow quite slowly, and it may take two more full years before a seedling is sufficiently large to plant in the landscape. The potted seedling should be moved into a sheltered location for each overwintering period (but not moved indoors).

Potting and Repotting Common Juniper

Small upright varieties of common juniper can make fairly good container plants for growing on a patio or deck. The container can be any material, though heavy materials such as clay pots may help prevent tipping. A large pot will allow your juniper to grow for two or three years before it needs to be repotted. Choose a container with a diameter at least 8 inches wider than the nursery container, and fill it with a blend of commercial potting mix and sand or perlite. This potting mixture blend will hold enough moisture, but will drain well enough to prevent root rot.

In colder climates, potted junipers may need to be moved into a sheltered location, or covered with mulch up to the lip of the container, for the winter months. Do not bring the plant indoors for the entire winter, as it requires a cold dormant period. But a potted juniper that is well established (two years or more in the pot), can be brought indoors temporarily to use as a living Christmas tree for no more than a week to 10 days. Too much time indoors, however, may kill the tree. Junipers are not as amenable to this use as are firs or other evergreen species.

Overwintering

Junipers are often chosen for the landscape because they are so cold-hardy and rarely experience problems with winter temperatures. However, it's possible that some cultivars may be sensitive to winter burn in far northern climates (zones 2, 3). In these areas, a thick layer of dry mulch (such as bark chips) and a windscreen made of burlap or landscape fabric may help protect the shrubs against winter burn. However, if your shrubs regularly experience winter damage, it's a signal you are growing the wrong varieties. Consult a local extension service or arboretum for advice on juniper cultivars guaranteed to perform well in your region.

Common Pests & Plant Diseases

Common junipers are susceptible to a number of common pests and diseases. Watch out for diseases such as juniper blight, twig blight, and cedar apple rust—all of which can be handled with prompt and aggressive pruning.

Common pests of the common juniper include bagworms, juniper scale, aphids, and more. Checking the shrub over semi-annually for signs of pests and using an insecticide when needed should keep any major infestations under control. 

Common Problems With Common Juniper

Tips of Branches Dying

Various blights caused by fungi can cause this symptom (see above). By the time such symptoms appear, it is too late to do much but trim off the affected branches. Applying fungicide early may prevent recurrance.

Leaves Die Back Along One Side of the Shrub

This is a classic symptom of winter burn, caused when sunlight and harsh winds desiccate the foliage on one side of the shrub. Many shrubs recover, gradually shedding the dead needles and replacing them with fresh new growth, but a badly burned shrub may perish.

Branches Die, Once at a Time

When entire branches die on a juniper shrub, it is often a sign of Phytophthora root rot, a fungal disease that chokes off the water supply to the shrub. By the time this symptom arrives, the disease is usually too far along to cure, though you can try pruning away damaged branches. This disease normally occurs in poorly draining soil, so if you choose to replant after removing the diseased shrub, make sure to amend the soil to create better drainage.

Needles Turn Brown, Gradually Fall Off

Needles that randomly turn brown and shed are often the result of too much, or too little, water. Another likely cause: damage from pets urinating on the shrub.