Blue rug juniper is a hardy evergreen plant with silvery-blue foliage that can take on a purplish tone in the winter months. Unlike the straight species, Juniperus horizontalis, ‘Wiltonii’, being a cultivar, often does not produce dark blue berries, which take two years to mature. With an intermediate growth rate, it reaches less than a foot tall and can spread several feet wide, forming a dense mat. The best time to plant blue rug juniper is in the cooler temperatures of fall or early spring. When the plants are mature, they require occasional watering and shaping. They typically don’t have issues with pests or diseases and are resistant to deer and air pollution. Just make sure the plants have adequate airflow and drainage, as most of their issues are caused by overly damp environments.
Light
Blue rug junipers prefer to grow in full sun, meaning at least six to eight hours of direct sunlight on most days. These plants can tolerate some shade and actually prefer protection from hot afternoon sun to prevent foliage burns. However, if located in too much shade, foliage will be sparse rather than full and lush.
Soil
Blue rug juniper is tolerant of a range of soil types, though it prefers to grow in dry, sandy soil with a pH range of 5.0 to 8.0. Excellent soil drainage is key to plant health. this shrub is tolerant of rocky soil, as well as salt from saltwater spray or road salt.
Water
Until a blue rug juniper plant matures, it’s necessary to keep the soil evenly moist (but not soggy). After becoming established, it prefers a moderate amount of soil moisture and can tolerate some drought. However, soil that’s too wet can kill the plant. So provide supplemental water to a mature plant only in extended dry spells or drought.
Temperature and Humidity
These plants can grow in a variety of temperatures and humidity levels. They can tolerate wide fluctuations of day-to-night temperatures as well as snow and frost. They’re best planted in the fall or early spring when the temperature is regularly below 60 degrees Fahrenheit. Planting in cooler weather enables the root systems to become established before hot and dry weather arrives. Moreover, particularly humid or wet weather can cause some stem dieback or root rot.
Fertilizer
Blue rug juniper grows well in average soil and is tolerant of somewhat poor soil. Fertilizer typically isn’t necessary, but to give mature plants a boost, apply an organic fertilizer in the fall following the product label instructions.
Types of Creeping Juniper
In addition to blue rug juniper, here are several other varieties of Juniperus horizontalis, commonly known as creeping juniper:
‘Bar Harbor’: This variety has blue-green foliage turning reddish purple in winter. It has a slow-to-medium growth rate.‘Blue Forest’: A compact variety that spreads one to five feet in ten years. Its foliage changes color from lavender in winter to blue in spring.‘Emerald Spreader’: This variety has bright emerald green foliage throughout the year. Although low-growing, it spreads to six feet wide or more.‘Green Acres’: As its name suggests, this variety grows lush dark green foliage.‘Monber’: This variety is also known as the ‘Icee® Blue’ juniper. It features dense silvery-blue foliage that sometimes turns purple in the winter.
Pruning
Blue rug juniper doesn’t require pruning unless growth has become unruly or portions of the plant are damaged or diseased. You can prevent the juniper from spreading outside of its boundaries by keeping it trimmed. Light pruning can also encourage robust growth and branching to create more fullness. In the spring, clean out any garden debris or trash that has lodged itself in this dense groundcover. Trim the juniper in the late winter or early spring when weather is dry. Remove any dead or damaged portions, and cut back long branches to shape them but by no more than a quarter of their length. Don’t prune all the way to bare stems growing in the center of the plant because this wood might be too old to put out new growth.
Propagating Blue Rug Juniper
You can propagate blue rug juniper from stem cuttings. Propagation from seed is not recommended because this is a cultivar and its seeds produce a plant that is different from the parent plant.
Potting and Repotting
Blue rug juniper is a groundcover with considerable spread so it is not suitable to be grown in pots.
Overwintering
This plant is native to Alaska, Canada, and the northern United States and, as such, is well-adapted to cold winters down to USDA cold hardiness zone 3. It does not need winter protection.
Common Pests and Plant Diseases
Blue rug juniper is not bothered by serious insect or disease problems. However, wet soil can lead to root rot, and in wet springs, the plant can get tip and twig blight, which causes younger needles to turn brown and drop off. It can also be a host plant to cedar-apple and other rust diseases. Sometimes it attracts aphids, bagworms, webworms, scale, and spider mites.
Common Problems
As part of the natural aging process, the centers of mature plants can die back in the center and become unsightly.
