<em>Cryptomeria</em>, Japanese cedar: planting, pruning and care

Description and botany

Cryptomeria japonica (syn. fortunei) belongs to family Taxodiaceae, like bald cypress (Taxodium distichum), American sequoias or Chinese Metasequoia, yet its leaves resemble those of no other conifer. They are pointed but not acute claws, about 1 cm long, arranged awl-like around the branchlet, their smooth and fairly supple texture suggesting plastic. The evergreen leaves are renewed after several years in a somewhat unusual way: whole branchlet sections brown before falling, a phenomenon known as decurtation, also observed in Araucaria.

Cryptomeria japonica reaches large dimensions, up to 30–55 m in height, with a very slender habit and rapid growth of around 6–8 m in 10 years in Japan’s rainy forests. Longevity may reach 1,000 to 2,000 years according to a specimen at Misaka shrine in Nagano, 30 m tall with a trunk 4 m in diameter at the base. Its reddish-brown bark peels off in vertical strips. Its distribution area in warm mountainous regions of Japan and southern China at 1,000–2,500 m altitude testifies to its great adaptability, especially as this species already existed in dinosaur times. Some variability exists between Japanese and Chinese specimens. Cryptomeria japonica var. sinensis has a less rigid habit thanks to finer branchlets. Japanese researchers have also observed that above 1,750 m Cryptomeria reproduces only by layering, whereas more favourable conditions also allow sowing, leading to greater genetic diversity.

Cryptomeria japonica – botanical illustration

The species has given rise to more than two hundred cultivars, including compact rounded dwarfs with very slow growth and very short needles like Vilmoriniana, or forms with soft, airy foliage such as Elegans or Elegans Viridis. Foliaged shoots of many cultivars often turn a red-bronze to rust colour in cold weather, a change that is exceptional in cultivar Elegans whose columnar habit reaches up to 9 m high by 2.40 m wide, or much more when it layers and forms a clump. Variety Cryptomeria japonica var. cristata produces fused, flattened shoots evoking a cockscomb, adding an incongruous note to the scene.

Flowering is monoecious: male aments form small terminal clusters during winter and release abundant pollen in February–early March. Female flowers form tiny green rosettes at branchlet tips that enlarge after fertilization to about 1.5 cm diameter by autumn before browning and releasing their seeds the following autumn. Each cone bears around forty scales ending in a recurved point.

Japanese cedar is widely used as an ornamental plant in temperate gardens worldwide, in Europe, India, North America and Australia, while it is an important forest species in Japan, China, the Azores and Réunion. It is the object of genuine veneration in Japan, notably at Nikko near Tokyo where almost 14,000 specimens, four centuries old, line a 37 km avenue. Its highly fragrant but fairly soft wood is prized for construction of temples and coffins in China, and is also used in furniture, building and woodwork because it resists attack by fungi and insects, probably thanks to its content of essential oil.

Main varieties of Cryptomeria

Varieties upright with moderate growth

Compact varieties in ball or conical form

Cryptomeria japonica Sekkan-Sugi

Graceful and distinctive conifer with semi-trailing branches clothed in light-green foliage, highlighted by young pale-yellow shoots becoming cream to almost white in winter. Its feathery branches, very soft to touch and sight, gracefully illuminate a semi-shaded corner.

• Height at maturity 6,50 m

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Cryptomeria japonica Yokohama

Dwarf evergreen conifer, habit rounded becoming conical with age, with slightly irregular growth. Extremely fine, dense foliage, almost crisped, pale green in summer, bronze-violet in winter. Its young tender-green shoots make it a very luminous plant in rockery or container under moderate sun.

• Height at maturity 1,10 m

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Cryptomeria japonica Vilmorin Gold

Dwarf conifer, habit rounded and compact, slightly irregular, with very dense evergreen foliage of a striking deep green adorned with superb golden shoots becoming cream in summer. This slow-growth variety, limited to 1 m, allows creation of unexpected, colourful combinations in sunny rockeries and alpine gardens.

• Height at maturity 1 m

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Cryptomeria japonica Vilmoriniana

Compact ball of bright green that, under cold, develops attractive brown and red tones. Reduced development in 30 cm container in all directions. Ideal to adorn small gardens, rockery or terrace. Grows in sun, in ordinary, well-drained soil, moisture ranging from not too dry to fresh.

• Height at maturity 90 cm

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Planting

Where to plant Cryptomeria?

Cryptomeria accepts an ordinary, fairly cool, well-drained, rather fertile soil, even slightly calcareous, neutral or acidic. Dislikes excessively dry or very shallow soil. It particularly favours the mild, humid climate of the Atlantic coast but acclimatises fairly easily elsewhere, although dimensions remain more modest.
Plant in full sun where climate permits except cultivars with light foliage such as Sekkan Sugi which do better in partial shade to avoid sun scorch. Position young plant sheltered from dry, cold winds that can scorch young shoots and in partial shade in southern regions. Minimum temperatures are about -15°C to -20°C depending on clones, noting branches do not cope well with snow weight.
Dwarf forms tolerate planting in a deep container which slows growth and helps keep habit even more compact. They are also suitable for rock gardens, not too sunny or exposed to wind however, as the plant seeks cool, humid air. Roots will be able to draw moisture from under rocks. Training as bonsai is common with Cryptomeria.

Male aments of a Cryptomeria japonica

When to plant?

Cryptomeria japonica is preferably planted from September to November and from February to June. In mild, wet climate, planting a specimen sold in a pot can be carried out almost all year round, avoiding periods of severe frost or very hot weather.

How to plant?

With young plants of small size (50 cm high), about 2 years old for example, establishment is very easy.

• Immerse pot in a bucket of water to thoroughly moisten it.
• Dig a hole 3 times wider than root ball and loosen soil around with tines of a garden fork.
• Add manure or compost to ensure good start for tree, which can grow quite rapidly.
• Place young plant in planting hole.
• Replace soil and firm lightly, forming a saucer.
• Mulch to maintain good moisture and pour at least 10 L of water.

In a deep, large container, place a drainage layer (gravel, clay balls, potsherds…), make a mix of 1/3 topsoil, 1/3 sand and 1/3 heather soil, turf or well-rotted compost. Mulch surface of pot.

Care

• Water Cryptomeria thoroughly during first 3–4 years and during prolonged drought. Plant becomes fairly self-sufficient quickly unless grown in a container. Remember to spray water regularly on plants trained as bonsai.
• Apply a special conifer fertiliser every year in April and hoe soil in summer to prevent capillary rise if no mulch.
• Leave dry twigs on soil to form natural mulch.
• Protect young plants with winter fleece if winters are cold.
• Pruning is not necessary. Dwarf forms can undergo a light pruning of shoots in March–April or late summer (August–September), as does Cryptomeria japonica ‘Elegans’, which hates short prunings!
• No diseases or pests reported on Cryptomeria in Europe. Armillaria root rot reported in some places such as Hawaii in warm, humid conditions.

Cones of Cryptomeria japonica

Multiplication

The simplest method of propagation is to propagate Cryptomeria and its cultivars by cuttings between August and October or to sow seeds of the type species in spring.

Propagation by cuttings

Prepare a deep pot by filling it with 50% turf and 50% sand.

• Take 15 cm long tips from August-ripened shoots, choosing the most vigorous.
• Remove needles from base of cutting.
• Dip base in plant hormone.
• Insert them to two-thirds of their length, avoiding contact between cuttings.
• Firm medium gently around each cutting to remove air pockets and ensure good contact between medium and cutting.
• Place them in a shaded, humidity-retaining environment, for example by placing a cut clear plastic bottle over them.
• Remove plastic after one month and keep your cuttings warm, protected from direct sun.
• Wait 4 to 6 months for sufficient root development.→ Discover our tutorial : How to propagate conifers?

Sowing

• Obtain seeds from a seed merchant.
• Stratify in the fridge for a few days.
• Sow them in a seed tray filled with potting compost mixed with sand.

Uses and companion plants

Varieties of Cryptomeria have often been selected for the colour variations they display through the seasons, from a very bright green in spring that darkens in summer then reddens, sometimes taking on fiery tones in cold weather, as with Vilmorinia or Elegans. Their globe-shaped forms in Compressa, conical in Yokohama, rather weeping in Sekkan Sugi, columnar in Elegans offer a range of possibilities for combining with other prostrate evergreen bushes or for forming a hedge. Don’t hesitate to plant them with bushes with small glossy, richly coloured leaves such as Abelia Sparkling Silver, Berberis darwinii or thunbergii Orange Dream or Golden Carpet. Heathers and other dwarf conifers with bluish tones such as Juniperus squamata Blue Star are among the many options to accompany Cryptomerias in a rockery or on a terrace. This plant, with its distinctive silhouette and leaf texture, pairs well with large stones, geometric lines and masonry work.

An autumn planting idea: Cryptomeria japonica ‘Sekkan Sugi’, Acer palmatum ‘Dissectum’, Acer palmatum ‘Shindeshojo’, Euonymus alatus and Picea glauca ‘Cecilia’

Cryptomeria japonica Sekkan Sugi, with its snow-covered-fir appearance, understated elegance and moderate growth up to 6.50 m high and 3.5 m wide, deserves a place in the garden. It can brighten semi-shaded areas or provide a low-maintenance bright backdrop to borders, thanks to its cream to near-white foliage in winter. It can thus showcase the flowering of a scented wild camellia such as Camellia lutchuensis.

The typical species Cryptomeria japonica, often endowed with several very straight trunks and an evergreen dark green, reptilian-looking foliage, is a remarkable specimen for medium-sized gardens that will make an impact when planted alone, especially as it retains modest dimensions around 10 m high and 3 to 5 m in diameter, or accompanied by maples, ginkgos or liquidambars to create a contrasting autumn scene.