Juniper plants (Juniperus species) are all coniferous evergreens, but they range widely in shape and form. Some junipers are only about 4 inches tall and are usually used as ground cover, according to Clemson University. Others are neatly rounded shrubs. Still others are towering in form, reaching heights of over 50 feet. Some of these tall trees have the common name of cedar, even though they of the Juniperus species. This is probably due to their cedar-like foliage.
Climate and Geography
The Juniperus family is so large that there are species found all over the world, according to Ohio State University. These trees vary widely in their hot and cold hardiness, but in general, juniper trees grow best in U.S. Department of Agriculture (USDA) plant hardiness zones 3 through 9. These plants do not grow as well in tropical or subtropical climates (USDA zones 10 and 11).
Juniper trees range widely in appearance, depending on the species and cultivar. Most have brown or gray peeling or exfoliating bark. The foliage can be tiny flat scales or needles and can range in color from bright green to blue or silver. In some species, the foliage turns brown or yellow in cold temperatures. The fruit is sky blue, dark blue, or silver-gray in color. The trees are either very wide and rounded, slender and shaped like a column or pyramidal in form.
Juniper trees need a least a half-day's worth of sunlight to grow well, according to Ohio State University. While these hardy trees can adapt to almost any type of soil, they grow best in moist, well-draining soils. Juniper trees do not grow well in full shade or in sites that are very wet, such as areas that collect standing water. Junipers will also tolerate heavy shearing and moderate pruning.
There are three main species of Juniperus trees that grow in the United States. J. ashei, or the Ozark white cedar, is the smallest, according to Clemson University. It grows to a maximum height of about 20 feet and has a pleasing, columnar shape. The berries are blue and the bark is gray and peels in attractive patterns. This is a hardy species that is resistant to cedar-apple rust. J. virginiana, or the Eastern red cedar, is native to the United States and reaches an average height of around 50 feet. This juniper has deep green foliage that turns reddish brown in cold temperatures. J. virginiana is known for its pleasant fragrance. J. silicicola is a wide tree that is often planted in groups for screening purposes. This tree, which is also known as the Southern red cedar, has a high salt tolerance, both in the soil and in the air, making it a good choice for coastal areas. J. silicicola reaches heights of 45 feet with a maximum width of 20 feet.
Juniper trees can suffer from a number of diseases and insect pests. Some are quite serious. Spider mites are a serious pest of juniper trees, as are scale and bagworms, according to Clemson University. All of these can damage a juniper tree beyond repair in as little as two or three seasons. Prevent and treat these insect infestations by using an insecticidal soap or oil in late winter, before new growth appears. Apply according to the directions on the label for the size and age of your tree. Junipers can also suffer from diseases. The best way to treat diseases is to prevent diseases from occurring in the first place. Treat your juniper with a fungicide in the spring to prevent fungal-based diseases such as twig blight and cedar-apple rust. If a fungus does take hold of your tree, prune off any branches that have growths on them, as these are the fruiting bodies of the fungi. This may help stop the spread of the disease.