Blue Rug Juniper Plants

Growing Tips and Care Guide

Wilton's Carpet is a type of creeping juniper.
David Beaulieu

Blue Rug juniper is a drought-tolerant ground cover once mature and craves fast drainage. Since many other plants find it difficult to thrive on sunny slopes, where water runs off so quickly that plants are apt to go thirsty, it is a practical solution for such problem areas. But to take advantage of its good qualities, you must first learn how to grow and care for it. 

Taxonomy and Botany of Blue Rug Juniper Plants

Plant taxonomy classifies Blue Rug juniper plants under Juniperus horizontalis. The cultivar is Wiltonii (thus the secondary common name of "Wilton's carpet"). These plants are low-growing evergreen shrubs. Plants in the Juniperus genus are grouped with the conifers, although, granted, most people would mistake the cones for berries. These berry-like cones are dark blue and used to flavor both cuisine and gin. The plants are also dioecious. They are just one type of creeping juniper.

What Blue Rug Juniper Plants Look Like

The foliage is a silvery-blue, thus the first half of its common name. The second half comes from its growth habit, as it forms a dense, low mat (rug), making it an ideal ground cover. It grows to be 4 to 6 inches tall, with a spread of 5 to 6 feet. Its foliage turns a purplish-bronze in winter. Blue Rug spreads rapidly, making it ideal for homeowners who are in a hurry to install ground covers on an incline to control erosion.

Care for Blue Rug Juniper Plants

No plant is "no-maintenance," but this one is certainly "low-maintenance." Ground covers that flower require much more care. Space these plants 4 to 6 feet apart to form a dense enough mat to crowd out weeds. To aid their weed-control efforts prior to maturity, make sure that they are well mulched (but do not pile up mulch over the plants' crowns). In fact, for better weed control, some people grow Blue Rug juniper in a bed covered with black plastic, poking holes in the latter to make room for the ground cover. Do not allow fallen leaves and branches to smother young plants (leaves can be blown off your planting with a leaf blower). Thin out mature plants for better air circulation, which will help avoid disease, but do not prune severely. Fertilize once in a while with manure tea if it looks like your ground cover could use a boost as the years go by.

This ground cover is fairly resistant to some of the diseases that trouble juniper shrubs. But spider mites can present a problem. One way to control spider mites on mature plants is to hose them down once in a while in summer with a firm spray. This will disrupt their web-making work.

If this does not do the trick and you spot a web entirely covering any of the plants, the safest policy is to sacrifice it for the good of the rest. Removing the infested plant will help prevent the spread of the spider mites to others. It is better to have to replace one plant than to lose all of them to this pest. If webbing appears on only one branch (which would suggest you caught the problem in time), prune off (and properly dispose of) this branch, and keep careful watch over the plants in case other webs appear.

USDA Planting Zones, Sun and Soil Requirements for Blue Rug Juniper Plants

This ground cover can be grown in planting zones 3 to 9. Blue Rug juniper plants thrive in full sun and prefer a well-drained soil with an acidic pH. Buying the plants from the garden center in summer and trying to transplant them at this time is not a good idea, as the heat of summer will stress your young ground covers and make it very difficult keep them watered well enough (until they become mature, it is critical that they have an evenly moist soil).

Before planting, prepare the ground with soil amendments. Those who garden in communities near the ocean will be glad to learn that these are salt-tolerant plants. This quality comes in equally handy if you live where it snows a lot in winter and you need to grow your ground cover along the road, because such areas tend to be salted by the highway department to clear the snow and ice in winter.

Uses, Ground Covers Similar to Blue Rug Juniper

Besides their use as ground covers, the juniper shrubs and their relatives make good specimens for a rock garden design. There are many types of junipers, and they come in a variety of heights, forms, colors (golds, blues, and greens), and textures. But note that not all junipers are suitable for ground covers. Some junipers are trees, while others fit the more usual image of "shrubs": plants that stand anywhere from knee-high to chest-high. Such plants are suitable for privacy screens and hedges.

The vine-like, low-growing junipers such as Blue Rug serve a different function. Although they can be grown on flat land, juniper ground covers are most prized as plants that can cover a sunny slope, where they serve three purposes all at once: erosion control, weed control, and eliminating the need to mow where footing is bad.

Other Juniper Ground Covers

Many varieties besides Blue Rug juniper plants are suitable for ground covers. All want full sun and a soil that drains well. The Prince of Wales cultivar of J. horizontalis is green and grows even more quickly, while another cultivar, Mother Lode, bears greenish-gold foliage. The Pancake cultivar stays smaller than these, both in terms of height (an amazing 2 to 3 inches tall) and spread (2 feet).

Other species of juniper with cultivars grown as ground covers are J. procumbens, J. squamata, J. chinensis, and J. conferta:

  • The Nana cultivar of J. procumbens has a height of 8 to 12 inches and a width of 6 feet, at maturity. The foliage is grayish-green or bluish-green. Grow it in zones 4 to 9.
  • The Blue Star cultivar of J. squamata provides another choice for those who seek that cool blue foliage. But Blue Star juniper will get taller over time (up to 3 feet) than Blue Rug and does not spread as much, proportionately (4 feet).
  • J. chinensis Sargentii is 18 inches to 2 feet tall at maturity, with a width of 7 feet. It bears green foliage and is suited to zones 4 to 9.
  • J. conferta Shore Juniper is so called because it tolerates the poor soils typical of coastal areas. Its height is 12 to 15 inches, its spread 8 feet. The leaves are greenish-gold. Grow it in zones 5 to 9.
Juniperus Squamata (Juniper horizontalis) and Heather grown as ground cover
Juniperus Squamata. Ron Evans / Getty Images