Blue Rug Juniper Plant Profile

blue rug juniper

The Spruce / Autumn Wood

Blue rug juniper (Juniperus horizontalis 'Wiltonii') is a drought-tolerant ground cover that craves good soil drainage. This juniper is a practical solution for sunny slopes where water runs off so quickly that plants are apt to go thirsty. Blue rug juniper is a hardy evergreen plant with silvery-blue foliage that can take on a purple tone in the winter months. With a moderate growth rate, it reaches less than a foot tall but can spread several feet wide, forming a dense mat. The best time to plant blue rug juniper is in the cooler temperatures of fall, winter, or early spring.

Botanical Name Juniperus horizontalis 'Wiltonii'
Common Name Blue rug juniper, creeping juniper, carpet juniper
Plant Type Evergreen shrub
Mature Size 3 to 6 inches tall and 6 to 8 feet wide
Sun Exposure Full sun
Soil Type Average, medium moisture, well-draining
Soil pH Acidic (but tolerates a range)
Bloom Time Nonflowering
Flower Color Nonflowering
Hardiness Zones 3 to 9
Native Area North America
blue rug juniper
The Spruce / Autumn Wood
blue rug juniper
The Spruce / Autumn Wood
blue rug juniper
The Spruce / David Beaulieu
Juniperus Squamata (Juniper horizontalis) and Heather grown as ground cover
Ron Evans / Getty Images

How to Grow Blue Rug Juniper

Blue rug juniper is certainly a low-maintenance plant. If you are growing it as a ground cover for a large site, space plants 4 to 6 feet apart. They will grow to form a mat that's thick enough to crowd out weeds and provide visual interest all throughout the year.

Once the plants are mature they will generally only require occasional watering and trimming to shape them. They typically don't have issues with pests or diseases and are even resistant to deer and air pollution. Just make sure the plants have adequate airflow and drainage, as most of their issues arise from overly damp environments.

Light

These plants prefer to grow in full sun, meaning at least six hours of direct sunlight on most days. However, they can tolerate a little bit of shade and actually prefer coverage from hot afternoon sun to prevent foliage burns. In too much shade, blue rug juniper will appear thin rather than lush.

Soil

Blue rug juniper is tolerant of a range of soil types, though it prefers to grow in sandy soil. Excellent soil drainage is key to healthy growth. Furthermore, this plant 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 that, the plant prefers a moderate amount of soil moisture and can tolerate some drought. However, soil that's too wet can kill the plant. So plan to water only if you've had an extended dry spell.

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, winter, or early spring when the temperature is regularly below 60 degrees Fahrenheit. That way the roots can 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, especially if you have rich soil. But to give mature plants a boost, you can use an organic fertilizer in the fall if you wish.

Propagating Blue Rug Juniper

You can propagate blue rug juniper by stem cuttings. Take a cutting that's around 4 to 6 inches long from a healthy stem between late July and October. Remove the needles from the bottom third of the cutting, dip the end in powdered rooting hormone, and plant it in a potting mix. Place the cutting in bright, indirect light in a warm room, and keep the soil moist. Root growth can take several months, so don't plant your cutting outside until the next spring.

Pruning

Blue rug juniper doesn't really need to be pruned unless the growth has become unruly or portions of the plant are damaged or diseased. However, you can prevent the juniper from spreading outside of your desired planting site by keeping it trimmed. Light pruning also can encourage robust growth and branching to create more fullness. Trim the juniper in the late winter or early spring when the weather is dry. Remove any dead or damaged portions, and cut back long branches to shape them ideally by no more than a quarter of their length. Don't prune all the way back to any bare stems growing in the center of the plant, as this wood might be too old to put out new growth.

Varieties of Creeping Juniper

In addition to blue rug juniper, there are several other varieties of Juniperus horizontalis. They include: 

  • 'Bar Harbor': This variety grows blue-gray foliage that can take on a purplish hue in the winter.
  • 'Blue Acres': This plant produces silvery-blue foliage that turns green with age. 
  • 'Emerald Spreader': This creeping juniper sports bright emerald green foliage year-round.
  • 'Green Acres': As its name suggests, this plant grows lush dark green foliage.
  • 'Monber': This variety features dense silvery-blue foliage that sometimes turns purple in the winter. 
Article Sources
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  1. Basic Principles of Pruning Woody Plants. University of Georgia Extension

  2. Juniperus Horizontalis 'Wiltonii'. Missouri Botanical Garden