Overview
Juniperus decumbens is a low, spreading evergreen conifer in the Cupressaceae family, growing 6–12 inches (15–30 cm) tall and spreading 4–8 feet (1.2–2.4 m) wide, forming a dense, ground-hugging mat. Branches radiate outward from the centre, layering along the ground and sometimes rooting at nodes. Foliage is primarily needle-like (juvenile type), arranged in whorls of three, 0.3–0.5 inch (8–12 mm) long, sharply pointed, grey-green to blue-green with a conspicuous white stomatal band on the upper surface. Scale-like (adult) foliage may appear on older growth. The species is native to the Bonin (Ogasawara) Islands and the Ryukyu Islands of southern Japan, where it occurs on rocky coastal cliffs and exposed headlands. In cultivation, it is grown primarily as the cultivar 'Nana', which forms an especially dense, compact mat 4–6 inches (10–15 cm) tall. Growth rate is slow — 2–4 inches (5–10 cm) of lateral extension per year. Berry-like seed cones are round, 0.25–0.3 inch (6–8 mm) in diameter, blue-black with a glaucous bloom, taking 2–3 years to ripen. Tolerates heat, drought, wind, and poor soil once established. Susceptible to juniper tip blight (Phomopsis juniperovora) and spider mites in hot, dry conditions.
Native Range
Juniperus decumbens is native to the Bonin Islands (Ogasawara Islands) and the Ryukyu Islands of southern Japan, where it occurs on exposed rocky coastal habitats, cliff faces, and thin soil over rock at low elevations.Suggested Uses
Planted as a groundcover on slopes, banks, retaining walls, and in rock gardens, spaced 3–4 feet (90–120 cm) apart. The prostrate habit cascades over walls and raised bed edges. Effective in containers (minimum 5 gallons / 19 L) as a trailing specimen. Tolerates coastal exposure and urban conditions. The dense mat suppresses weeds once established.How to Identify
Appearance
Size & Dimensions
Height6" - 1'
Width/Spread4' - 8'
Reaches mature size in approximately 5 years
Bloom Information
Male pollen cones are small, yellowish, 2–3 mm long, releasing pollen in spring (March–April). Female seed cones are inconspicuous at pollination, developing over 2–3 years into round, blue-black berry-like cones 0.25–0.3 inch (6–8 mm) in diameter with a glaucous bloom. Cones ripen in the second or third year after pollination.Detailed Descriptions
Foliage Description
Grey-green to blue-greenGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Plant in full sun in well-drained, lean to moderately fertile soil with a pH of 5.5–7.5. Space 3–4 feet (90–120 cm) apart for groundcover coverage within 3–5 years. Amend heavy clay with coarse grit to improve drainage. Water regularly during the first growing season; once established, the species is drought-tolerant and requires supplemental irrigation only during extended dry periods. No fertilisation is needed in average soil — excess nitrogen promotes lax growth. Mulch with gravel or stone chips rather than organic material to prevent moisture accumulation around the crown. Monitor for spider mites in hot, dry weather — a strong water spray dislodges mites from the underside of foliage.Pruning
No routine pruning is required. Remove dead or browning branches at their point of origin. To contain spread, cut back extending branches to a side branch within the desired outline in early spring. Do not shear — the natural layered habit is lost with formal trimming.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
early spring
Maintenance Level
very lowContainer Growing
✓ Suitable for container growing
Minimum container size: 5 gallons