A dwarf conifer with fine dark-green foliage and congested growth habit. The name means "green ball" in Japanese. Prefers sun/partial shade in well-drained soil. 2' tall x 2' wide in 10 years. Hardy to -20 degrees. USDA zone 5.
 
Attribution from The American Conifer Society:
Cryptomeria japonica 'Ryoku Gyoku' / Ryoku Gyoku Japanese cedar
RECOMMENDED HARDINESS ZONES:
7 (10 to 0 F / -12.2 to -17.8 C)
HORTICULTURAL STATUS: Established
ORIGIN: Witch's Broom
COLOR: 
TRINOMIAL TYPE: Cultivar
GROWTH SHAPE: Globe or Globose
GROWTH SIZE: Miniature: less than 1 inch (2.5 cm) per year / less than 12 inches (30 cm) after 10 years
 
Cryptomeria japonica 'Ryoku Gyoku' / Ryoku Gyoku Japanese cedar
Cryptomeria japonica 'Ryoku Gyoku' is a irregular-globose, extremely slow-growing selection of Japanese cedar with dense, miniature dark-green awl-like foliage that will assume a light-bronzy cast in winter in colder climates. After 10 years of growth, a mature specimen will measure, at best 8 to 10 inches (20 - 25 cm) tall and wide, an annual growth rate averaging less than 1 inch (2.5 cm).
 
Origin:
This cultivar originated as a witch's broom found in the late 1990s on a containerized specimen of C. japonica 'Tansu' by Edsal Wood of Aurora, Oregon, USA at his nursery, Bonsai Village. The cultivar names loosely translates into "Jade Ball" in the Japanese language.