About Juniperus horizontalis Moench
Juniperus horizontalis Moench matches both its scientific and common names with its low, spreading growth habit: it only grows 10–30 centimetres (3+7⁄8–11+3⁄4 inches) tall, but often spreads several metres wide. Its shoots are slender, with a diameter of 0.7–1.2 millimetres (1⁄32–1⁄16 inch). Leaves are arranged in opposite decussate pairs, or occasionally in whorls of three. Adult leaf blades are scale-shaped, 1–2 mm long (reaching up to 8 mm on lead shoots) and 1–1.5 mm (1⁄32–1⁄16 inch) broad, growing from an adnate petiole. Juvenile leaves, which only grow on young seedlings, are needle-shaped and 5–10 mm (3⁄16–3⁄8 inch) long. The species produces berry-like cones that are shaped from globose to bilobed, 5–7 mm (3⁄16–9⁄32 inch) in diameter, dark blue with a pale blue-white waxy bloom. Each berry-like cone holds two seeds, rarely one or three; these cones usually have a curved stem and mature after around 18 months. Male cones measure 2–4 mm (3⁄32–5⁄32 inch) long, and shed their pollen in early spring. Juniperus horizontalis is dioecious, so each individual plant produces only one sex of cone. It is closely related to Juniperus virginiana, and often hybridizes with this species where their ranges overlap in southern Canada. Hybrids with Juniperus scopulorum also occur. This species is native to northern North America. It grows throughout most of Canada, from Yukon east to Newfoundland. In the United States, it is found in Alaska, and from Montana east to Maine in the continental US; its southernmost distribution reaches Wyoming and northern Illinois. One of the habitat types it occupies is rocky areas on the east slopes of the Rocky Mountains. More than 100 distinct cultivars of Juniperus horizontalis have been selected for use as ornamental garden plants. Its strictly prostrate growth habit is valued for use as ground cover. Popular cultivars include 'Bar Harbor', 'Blue Acres', 'Emerald Spreader', 'Green Acres', and 'Wiltonii', also sold as "Blue Rug Juniper". Many of the most popular cultivars have noticeably glaucous foliage, while others have bright green, yellowish, or variegated foliage.
