Japanese cedar

Identification and origin

Cryptomeria japonica belongs to the cypress family, Cupressaceae. It is the only species in its genus. Its native range covers Japan and south-central and southeastern China, where it grows in cool, moist regions. It has been planted in many countries and has become established outside its range, for example in the Azores, Great Britain, Italy and New Zealand. In Japan it is called sugi. Despite the name “Japanese cedar,” it is not related to the true cedars of the genus Cedrus.

In the wild it can reach 164 ft tall. In cultivation it usually grows 49–69 ft tall and 19.5–29.5 ft wide, over twenty to fifty years. Growth is slow to medium and the tree is remarkably long-lived: some Japanese specimens are about 650 years old. The habit is conical to pyramidal, soft and graceful, on a straight trunk that tapers toward the top. The branches grow in whorls and are horizontal to slightly drooping.

The awl-shaped needles are about 0–1 in long. Arranged in spirals around the shoots, they curve in toward the branch with a slight twist. Their color ranges from bright green to blue-green, and they stay on the tree for four to five years. On the same branch, the first needles of the year are shorter than later ones. In winter, the foliage often takes on bronze tones.

The fibrous reddish-brown bark peels in long vertical strips and is part of the tree’s appeal. Male and female cones grow on the same tree. Male cones cluster at the tips of the shoots; the round female cones, about 1 in across, turn from green to brown as they ripen.

There are around fifty cultivars, from columnar trees to dwarf mounds. ‘Elegans’ forms a broad column 15–19.5 ft tall with good winter color. ‘Yoshino’ is a large, narrow tree with blue-green foliage. ‘Black Dragon’ has very dark green foliage and ‘Sekkan-sugi’ yellowish-white new growth. The rounded ‘Globosa Nana’ turns rusty red in winter, and ‘Tenzan’ forms a mound less than 12 in tall. It is sometimes confused with Norfolk Island pine (Araucaria heterophylla). Its wood is highly valued for building.

Light

Japanese cedar prefers full sun, with at least six hours of direct sun a day, but it tolerates partial shade and dappled light. Good air circulation helps prevent foliage diseases. Still, choose a spot sheltered from strong winds.

Watering

In the ground, it likes moist soil. An established tree is moderately drought tolerant, but it needs watering during long dry spells.

In a container or as bonsai, its needs rise sharply: the root ball must never dry out during the growing season. Check the soil often and water as soon as the surface starts to dry. Japanese cedar likes humid air and does poorly in dry heat. Rainwater is a good choice if your tap water is very hard.

Potting mix

It grows best in moist, well-drained, rather acidic soil rich in organic matter, but it adapts to many soil types, including clay, loam, sand and even chalk, as long as water does not stand. In a pot, use a free-draining mix with a pH between 5.5 and 7.

Temperature

Japanese cedar is very hardy in the ground: it survives winters down to 5–-4 °F and suits cool temperate climates as well as milder regions. Intense dry heat suits it less than the humid summers of its native range.

In a pot, the roots are much more exposed, so the tree tolerates little frost, especially in a shallow container. Protect it in winter, ideally in a cold but frost-free greenhouse. Winter bronzing of the foliage, stronger in full sun and hard cold, is normal: the green color returns in spring.

Repotting

In the ground, plant it in moist, well-drained soil, sheltered from strong winds.

In a pot, repot a young tree every two to three years in mid-spring, as the buds start to extend; an older tree can wait longer. Its roots grow at a moderate pace, so avoid severe root pruning.

Pruning

In the ground, no pruning is needed: the tree naturally keeps its conical outline. Simply remove dead or damaged wood. Unusually for a conifer, it tolerates coppicing, meaning being cut back close to the ground, and then regrows from the stump.

Grown as bonsai, it responds well to pinching and readily forms new buds. The techniques specific to that practice are covered in the Japanese cedar bonsai guide.

Propagation

• Seed: sow outdoors in spring.
• Cuttings: semi-ripe cuttings root very easily from late summer to early fall. This is the method of choice to keep the traits of a cultivar.
• Air layering: also possible.

Common problems

Japanese cedar is usually tough and rarely bothered by insects. Still, the same symptom can have several causes: look at the whole tree and its growing conditions before acting.

• Brown or reddish needles in winter: often just winter bronzing, which is harmless and fades in spring.
• Spots or browning of the foliage, especially inside the canopy: needle diseases, blights and leaf spots caused by fungi; good airflow through the foliage helps prevent them. On a large tree, a treatment is hard to apply properly.
• General decline, brown roots: Phytophthora root rot, favored by waterlogged soil; more rarely, honey fungus.
• Dull, speckled needles: spider mites; misting the foliage regularly helps prevent them. Scale insects can also settle in.

The tree also resists deer and rabbits and tolerates some salt.

Toxicity

No toxicity has been reported: Japanese cedar does not appear among the plants listed as toxic to dogs and cats by veterinary references. Still, keep children and pets from chewing its needles or cones.