Japanese red cedar (Cryptomeria japonica) is a tree native to Japan. Japanese red cedar has a notable fragrant and aesthetically pleasing color. Commercially, japanese red cedar is used for wooden construction materials for interior design. It can also be grown as a bonsai.
I. Appearance and Characteristics
Cryptomeria (literally “hidden parts”) is a monotypic genus of conifer in the cypress family Cupressaceae. It includes only one species, Cryptomeria japonica (syn. Cupressus japonica L.f.). It used to be considered by some to be endemic to Japan, where it is known as Sugi (杉). The tree is called Japanese cedar or Japanese redwood in English. It has been extensively introduced and cultivated for wood production on the Azores.
Cryptomeria is a very large evergreen tree, reaching up to 70 m (230 ft) tall and 4 m (13 ft) trunk diameter, with red-brown bark which peels in vertical strips. The leaves are arranged spirally, needle-like, 0.5 – 1 cm (1⁄4–3⁄8 in) long; and the seed cones globular, 1–2 cm (1⁄2–3⁄4 in) diameter with about 20–40 scales. It is superficially similar to the related giant sequoia (Sequoiadendron giganteum), from which it can be differentiated by the longer leaves (under 0.5 cm or 1⁄4 in in the giant sequoia) and smaller cones (4–6 cm or 1+1⁄2–2+1⁄4 in in the giant sequoia), and the harder bark on the trunk (thick, soft and spongy in giant sequoia).
II. How to Grow and Care
Sunlight
Japanese cedars enjoy the sunlight; however, they tolerate some shade or filtered sun. The tree will thrive and perform its best in full sun, ideally six hours of direct sunlight daily.
Temperature and Humidity
Japanese cedar is well suited for USDA zones 5 to 8 and is quite hardy in winter and mild heat. One thing that needs to be considered is the possible winter browning in Cryptomeria japonica. The browning is due to photoinhibition, which occurs when the tree is under high-light and low-temperature conditions.
It is not tolerant of pollution and will not thrive in an environment with poor-quality air.
Watering
After it is established, the Japanese cedar will be somewhat drought-tolerant. However, when young, these trees will require regular watering to supplement the rain for the tree to thrive. When planted in average soil and a location that gets a good amount of summer rain, you should not have to water your new tree daily unless faced with drought conditions.
Soil
While it prefers rich, acidic, consistently moist but well-drained soil, C. japonica will grow in most average, well-drained soil. Drainage is critical, as soggy soil will lead to root rot or other diseases.
The Japanese cedar is somewhat fussy when pH is concerned. It grows well in acidic to neutral soil. It might be a good idea to test the soil in the planting area to determine if it is suitable for a Japanese cedar. If the pH is too high, hope is not lost—a soil’s pH can be lowered by applying soil sulfur, chelated iron, or organic compost.
Fertilizing
The evergreen will benefit from some fertilization. When feeding the Japanese cedar, use a slow-release fertilizer for trees and shrubs in late winter or early spring. For the amount to use, follow product label instructions.
Pruning
The best time to prune Japanese cedar is mid spring to summer; do not prune in winter. However, removing any dead or diseased branches at any time of year is OK.
These trees can be maintained as bonsai trees. Otherwise, they do not require much pruning, but pinching off new growth results in a fuller, bushier appearance and encourages new growth. Never remove more than 1/3 of a tree in one season.
Cut away overlapping branches in the tree’s center to improve airflow, preventing fungal growth and insect problems. Japanese cedars are sensitive to pruning, so it’s best to mist the tree and prune on mild days with no other mitigating factors like the scorching sun or high winds.
Propagation
Cuttings
Japanese cedar is best propagated by semi-hardwood stem cuttings in late summer. It can also be grown from seed. Here’s how to grow it from cuttings:
- You’ll need pruning snips, a knife, rooting hormone, compost-enriched potting soil, and a cold frame or pot with ample drainage.
- Pull off or diagonally snip a healthy 3- to 4-inch cutting, like a side shoot from the main stem. Keep a strip of bark from the parent plant intact.
- Remove the lower leaves from the cutting by at least 1/3 of its foliage.
- Use the knife to score the stem with 2-inch vertical lines and coat all the cut wounds with rooting hormone.
- Plant the cut end of the stem cutting in the potting soil in a cold frame or pot that can be sheltered for the first winter season.
- Water thoroughly and keep the soil moist but not soggy. Give sunlight but protect it from overly hot sunny days or harsh winds in a sheltered spot for its first year.
Seed
Japanese cedar seeds can be started indoors year-round. Here’s how:
- Before sowing, cold stratify the seeds in moist soil or sand in the refrigerator to cool down for at least four weeks. The cooling period, followed by warmth, spurs the seeds to germinate.
- Warm the seeds by soaking them in lukewarm water for 12 to 24 hours.
- Spread seeds on a bed of fresh soil. Loosely cover with moist soil, Cover to keep humidity high, which aids germination success.
- It can take two to four weeks for seeds to sprout. Keep protected from extreme temperatures, scorching sun, wind, and soggy conditions for at least the first year of growth.
Potting and Repotting
Japanese cedars can be kept as potted plants while small and can be trained to grow as bonsai with well-manicured pruning. They require good drainage, so use pots with ample drainage holes and well-draining soil. Most soils can be amended with perlite to improve drainage. For new stem cuttings, you can start with an 8-inch pot.
If you allow this tree to grow fully, it will eventually outgrow pots and need planting in the ground. It will need transplanting into larger pots every two to three years during the young growth phase. To repot, ensure the new pot can accommodate the root ball plus 8 inches of width.
Overwintering
Winter and cold temperatures are not a problem for established Japanese cedars; however, young trees need protection from climate extremes, like plunging temperatures and harsh winds. Hardy down to USDA zone 5 (-20 degrees Fahrenheit), Japanese cedars would benefit from the protection of a cold frame for the first one to two years of growth. Put it in a sheltered spot if it’s not in a cold frame.
Pests and Diseases
Common Pests and Plant Diseases
Japanese cedars are relatively problem-free but can get minor insect problems like mites and fungal diseases like leaf blight and leaf spot. Also, soggy soil can invite root rot. Sometimes, the Japanese cedar long-horned beetle can be a problem. They are slower to form infestations and can be treated with pyrethrin-based products to eliminate them.
Leaf blight looks like interior foliage turning brown, black, or gray. To avoid this fungal issue, ensure this tree receives morning sun to dry its dew-laden foliage. Leaf spot looks like brown or purple spots on the foliage; eventually, it forms yellow rings around the spots, and the leaves start to die.
Fungal sprays can help keep this fungal problem away. Also, prune away excessive interior branches so the tree has ample airflow to its foliage. Leaf blight can kill young trees if not treated immediately.
Common Problems
The Japanese cedar is a relatively easy plant to care for once established in suitable soil with plenty of room to grow.
Browning Foliage
In places where temperatures drop below freezing, it’s common for Japanese cedar foliage to turn reddish-brown. It may seem as if the foliage is dying, but this color change is how the plant handles the winter weather. Unlike deciduous trees that change colors and lose their leaves, the foliage remains and will turn green again in the spring.
Unseasonal browning (spring or summer), browning of interior foliage, or browning leaf tips may be signs of a fungal disease.
III. Uses and Benefits
- Timber
Cryptomeria japonica timber is extremely fragrant, weather and insect resistant, soft, and with a low density. The timber is used for the making of staves, tubs, casks, furniture and other indoor applications. Easy to saw and season, it is favored for light construction, boxes, veneers and plywood. Wood that has been buried turns dark green and is much valued. Resin from the tree contains cryptopimaric and phenolic acid.
The wood is pleasantly scented, reddish-pink in color, lightweight but strong, waterproof and resistant to decay. It is favoured in Japan for all types of construction work as well as interior paneling, etc. In Darjeeling district and Sikkim in India, where it is one of the most widely growing trees, C. japonica is called Dhuppi and is favored for its light wood, extensively used in house building.
In Japan, the coppicing method of daisugi (台杉) is sometimes used to harvest logs.
- Ornamental
Cryptomeria japonica is extensively used in forestry plantations in Japan, China and the Azores islands, and is widely cultivated as an ornamental tree in other temperate areas, including Britain, Europe, North America and eastern Himalaya regions of Nepal and India.
The cultivar ‘Elegans’ is notable for retaining juvenile foliage throughout its life, instead of developing normal adult foliage when one year old (see the picture with different shoots). It makes a small, shrubby tree 5–10 m (16–33 ft) tall. There are numerous dwarf cultivars that are widely used in rock gardens and for bonsai, including ‘Tansu’, ‘Koshyi’, ‘Little Diamond’, ‘Yokohama’ and ‘Kilmacurragh.’
