<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 claws, not acute, about 1 cm long, arranged in a comb around the branchlet, their smooth and fairly flexible texture suggesting plastic. The evergreen leaves are renewed after a few years in a rather particular way: whole portions of branchlet brown and fall off, a phenomenon known as decurtation, also observed in Araucaria.

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

Cryptomeria japonica – botanical illustration

Species has given rise to more than two hundred cultivars, including compact dwarf rounded forms with very slow growth and very short needles such as Vilmoriniana, or forms with soft, airy foliage like Elegans or Elegans Viridis. Leafy branchlets of cultivars often turn a red-bronze to rust colour in cold weather, an effect 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 thicket! Variety Cryptomeria japonica var. cristata produces fused, flattened shoots evoking a cockerel’s crest, adding an incongruous note to the scene.

Flowering is monoecious: male aments form small terminal clusters during winter that release abundant pollen in February–early March. Female flowers form tiny green rosettes at tips of branchlets 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 tree in temperate gardens worldwide — in Europe, India, North America or Australia — while also being an important forest species in Japan, China, Azores and Réunion. It enjoys genuine veneration in Japan, notably at Nikko near Tokyo where an alignment of nearly 14,000 specimens, four centuries old, stands along a 37 km avenue. Its highly scented but rather soft wood is prized for temple building and coffins in China, and is also used in furniture, construction and panelling, as it resists attacks by fungi and insects, probably thanks to its content of essential oil.

Main varieties of Cryptomeria

Erect varieties of moderate growth

Compact globe-shaped or conical varieties

Cryptomeria japonica Sekkan-Sugi

Graceful, original conifer with semi-trailing branches covered in light green foliage trimmed with young shoots pale yellow turning cream to almost white in winter. Its feathery-looking branches, very soft to touch and to the eye, gracefully illuminate a semi-shaded corner.

• Height at maturity 6,50 m

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Cryptomeria japonica Yokohama

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

• Height at maturity 1,10 m

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Cryptomeria japonica Vilmorin Gold

Dwarf conifer, rounded, compact and slightly irregular habit, with very dense evergreen foliage of clear rich green, adorned with superb golden shoots turning 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 globe of bright green that develops attractive brown and red hues in cold weather. Restricted growth to 30 cm in all directions in a 30 cm container. Ideal for adorning small gardens, rockeries or terraces. Grows in sun, in ordinary well-drained soil, from slightly dry to fresh.

• Height at maturity 90 cm

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Planting

Where to plant Cryptomeria?

Cryptomeria tolerates ordinary, fairly fresh, well-drained, rather fertile soil, even slightly calcareous, neutral or acidic. It dislikes excessively dry or very shallow soils. It particularly favours the mild, humid climate of the Atlantic coast but acclimatises fairly easily elsewhere, although size remains more modest. Plant in full sun where climate allows, except cultivars with light-coloured foliage such as Sekkan Sugi, which do better in partial shade to avoid sunburn. Place the young plant sheltered from dry, cold winds that can scorch young shoots, and in partial shade in southern regions. Minimum temperatures are around −15°C to −20°C depending on clones, noting that branches cope poorly with weight of snow.
Dwarf forms accept planting in a deep container, which slows growth and helps keep an even more compact habit. They also suit rockeries, though not too sunny or exposed to wind, as the plant seeks atmospheric freshness. Roots can draw moisture from beneath rocks. Training as bonsai is common for Cryptomeria.

Male aments of Cryptomeria japonica

When to plant?

Cryptomeria japonica is best planted from September to November and from February to June. In mild, well-watered climates, planting a potted specimen can be done almost all year, avoiding periods of severe frost or extreme heat.

How to plant?

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

• Immerse pot in a bucket of water to thoroughly moisten it.
• Dig a hole three times wider than the rootball and loosen the soil around it with the tines of a digging fork.
• Add well-rotted manure or compost to ensure a good start for the tree, whose growth can be fairly rapid.
• Place the plant in the planting hole.
• Replace soil and firm gently, forming a saucer-shaped depression.
• Mulch to retain moisture and pour at least 10 litres of water.

In a deep, large container, place a drainage layer (gravel, clay pebbles, broken pottery…), 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 generously for the first 3-4 years, and during prolonged drought. Plant becomes quite self-sufficient quickly except when grown in a container. Remember to mist water regularly on plants trained as bonsai.
• Apply a special conifer fertiliser every year in April and hoe soil in summer to avoid capillary rise if you do not have mulch.
• You can leave dry branches fallen on soil to form natural mulch.
• Protect young plants with winter fleece if winters are cold.
• Pruning is not necessary. Dwarf forms may receive a light pruning of branches in March–April or at end of summer (August–September), as does Cryptomeria japonica ‘Elegans’, which hates short prunings!
• No diseases or pests reported on Cryptomeria in Europe. Root rot (Armillaria) is reported in some countries such as Hawaii under hot, humid conditions.

Cones of Cryptomeria japonica

Multiplication

The simplest propagation is to propagate Cryptomeria and its cultivars by cuttings between August and October, or 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 of August-ripened shoots from the most vigorous stems.
• Remove needles from base of each cutting.
• Dip base in plant hormone for cuttings.
• Plant them to two-thirds of their length, avoiding contact between them.
• Firm soil gently around each to remove air pockets and ensure good contact between potting compost and cutting.
• Place them under cover in shade, for example by placing a cut transparent plastic bottle over them.
• Remove plastic after one month and keep cuttings warm, protected from direct sunlight.
• Wait 4 to 6 months for sufficient rooting.→ Discover our tutorial : How to take cuttings from conifers?

Sowing

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

Uses and plant associations

Cryptomeria varieties 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 hues in cold weather, as with Vilmorinia or Elegans. Their ball-shaped forms in Compressa, conical in Yokohama, somewhat weeping in Sekkan Sugi, columnar in Elegans offer a range of possibilities for pairing them with other low-growing evergreen bushes or to form a hedge. Don’t hesitate to plant them with bushes bearing small glossy leaves richly coloured 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 possible companions to accompany Cryptomeria in a rockery or on a terrace. This plant, with its distinctive silhouette and foliage texture, works well with large stones, geometric lines and masonry features.

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

Cryptomeria japonica ‘Sekkan Sugi’, with its snowy fir-like aspect, discreet elegance and moderate growth to 6.50 m high by 3.5 m wide, deserves a place in the garden. It can enliven semi-shaded areas or provide a bright, low-maintenance backdrop for a bed, thanks to its cream to almost white winter foliage. It can thus showcase the flowering of a scented wild camellia such as Camellia lutchuensis.

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