How to Grow and Care for Japanese Cedar

Japanese cedar, also commonly known as suji or by its botanical name Cryptomeria, is an evergreen conifer and national tree of Japan. It is called a cedar but is a cypress tree. It is a monotypic genus or a one-of-a-kind tree with all-season visual interest that grows upright, with a straight trunk, and is prized for its pinkish, aromatic timber. It grows best in full sun, requiring about six hours of sunlight and moist, rich, acidic soil, and can handle below-freezing winters and mild heat.

Japanese Cedar Tree Care

Here are the main care requirements for growing a Japanese cedar:

• Provide full sun, with at least six hours of light; tolerates filtered sun.
• Plant in acidic to neutral soil that is consistently moist and well-draining.
• Water regularly when young; becomes drought resistant as an older tree.
• Give fertilizer once a year in the spring for the best results.
• Plan for it to eventually grow large, requiring at least 30 feet of width.

Light

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.

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.

Water

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. 

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.

Fertilizer

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.

Types of Japanese Cedar

Japanese cedar trees have billowy, plume-like foliage, pretty peeling bark, cones, and a tendency to form multiple arrow-straight trunks. Japanese cedar can reach massive sizes and live centuries long. Dwarf Japanese cedar cultivars are no taller than a foot or two. Golden Japanese cedars appear yellow or gold, providing a nice contrast next to other evergreen varieties.

The tallest Japanese cedars have reached up to 230 feet, while the oldest, a tree named Jomon Sugi on Yakushima Island in Japan, is believed to be between 2,170 to 7,000 years old.

• 'Kilmacurragh': A dwarf cultivar with a mounding form with bright green foliage on young growth
• 'Black Dragon': A smaller tree with a wide pyramidal form with dense, dark green, nearly black foliage
• 'Elegans': Very popular cultivar; can be used as a shrub or small tree, with notable brownish-red foliage in winter that adds to its seasonal interest
• 'Golden Promise': Dwarf cultivar has a coarse texture with bright yellow foliage covering its small globular shape
• 'Spiralis': Twisted, wiry foliage on densely packed branches; starts young in a rounded shape and eventually establishes a leader and takes on a mature upright habit

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.

Propagating Japanese Cedar

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:

1. You'll need pruning snips, a knife, rooting hormone, compost-enriched potting soil, and a cold frame or pot with ample drainage.
2. 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.
3. Remove the lower leaves from the cutting by at least 1/3 of its foliage.
4. Use the knife to score the stem with 2-inch vertical lines and coat all the cut wounds with rooting hormone.
5. 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.
6. 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.
   

How to Grow Japanese Cedar From Seed

Japanese cedar seeds can be started indoors year-round. Here's how:

1. 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.
2. Warm the seeds by soaking them in lukewarm water for 12 to 24 hours.
3. Spread seeds on a bed of fresh soil. Loosely cover with moist soil, Cover to keep humidity high, which aids germination success.
4. 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 Cedar

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.

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 With Japanese Cedar

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.