Japanese larch

Identification and origin

Larix kaempferi belongs to the Pinaceae, the family of pines and firs. It is native to Japan, specifically to the mountains of central Honshu. There it grows in mixed temperate mountain forests and climbs to the tree line: high on the southern face of Mount Fuji it forms stunted, twisted trees that look like bonsai. It reached Western gardens in 1861 and has naturalized in much of northern and central Europe, as well as in Newfoundland and New York. It was long planted for its strong, heavy, durable timber, and because it resists larch canker better than European larch. The species name honors Engelbert Kaempfer, a German botanist who visited Japan in the late 1600s. It is also found under its former name, Larix leptolepis.

It is a large tree, broadly conical at first, becoming open and irregular with age. In cultivation it typically reaches 70–90 ft tall and 25–40 ft wide; in the wild it can exceed 98.5 ft. Its slender main branches spread almost horizontally and curve upward at the tips, while the secondary branchlets hang down.

Unlike most conifers, it is deciduous. Its soft, narrow needles, about 1–2 in long and gray-green to dark green, have two white bands on the underside. They grow in tufts of roughly twenty to forty on short spur shoots, and singly along the long shoots. In fall they turn golden yellow or orange, then drop before winter. The best way to tell it from European larch is the color of the young twigs in winter: reddish brown in Japanese larch, yellowish in its cousin.

In spring, small reddish female flowers appear along with smaller, yellow, catkin-like male flowers. The upright, almost globe-shaped cones measure 1–1 in. Green or purplish at first, they ripen to golden brown; their scales, clearly turned outward, are distinctive. They stay on the tree all winter. The gray bark, rusty brown inside, peels off in long strips; on old trees it becomes thick and fissured.

Cultivars include ‘Blue Dwarf’ and ‘Nana’, dwarf and rounded; ‘Jakobsen’, compact, with young stems that turn pink in winter; and ‘Diana’, with corkscrew branches.

Light

Japanese larch needs full sun, meaning at least six hours of direct sun a day. It tolerates light shade but not deep shade, which weakens it. A south- or west-facing site suits it, exposed or sheltered; protection from strong winds is still preferable.

Watering

It needs steady moisture and tolerates neither drought nor dry soils. In the garden, choose a spot where the soil stays moist year-round.

In containers and as bonsai, water thoroughly as soon as the surface of the soil starts to dry, until water runs out of the drainage holes, without leaving the root ball soggy. In full sun in summer, it can get very thirsty. Avoid very hard water: in hard-water areas, use rainwater.

Potting mix

It grows best in moist, acidic, well-drained soil rich in organic matter. It tolerates neutral soil and adapts to clay, loam or sand, as long as drainage is good and the soil does not dry out.

For bonsai, use a free-draining mineral mix that is neutral or slightly acidic, based on akadama, pumice and lava rock.

Temperature

It is a very hardy tree, suited to USDA zones 4a to 7b and rated among the plants that survive the harshest continental winters, below -4 °F. It prefers a climate like that of its native mountains: cool summers and cold winters. It handles summer heat and humidity somewhat better than European larch, but still struggles in hot, humid summers.

As a bonsai it spends the winter outdoors. It needs no protection until the cold drops below 5–-4 °F; above all, shelter it from excessive rain that soaks the root ball.

Repotting

Young trees transplant easily in the ground. In containers, the roots resent disturbance: for bonsai, repot a young tree every two years and an old one every three to five years, just before the buds turn green, in full winter dormancy or in fall. Do not bare-root and never remove more than one third of the roots. Do not repot a frozen root ball; the roots themselves are very cold-hardy.

Pruning

For a conifer, it is very vigorous and quickly replaces a pruned shoot. Prune large branches in winter or early spring, before growth resumes. Its sticky resin protects wounds and it heals quickly, without cut paste. On bonsai, long summer shoots are shortened once they reach 4–6 in; it suits almost every style except the broom.

Propagation

Seed is the recommended method. Sow in early spring; seedlings grow slowly for the first two or three years, then very fast. Semi-ripe cuttings in summer or hardwood cuttings in winter are possible but root with difficulty. Air layering works well in late spring.

Common problems

First of all, don’t worry in fall: yellowing and then dropping all its needles is normal for this deciduous conifer. Outside that season, browning or needle drop can have several causes: drought, overwatering, sun scorch, pests or disease.

• Pests: larch case-bearer, larch sawfly and redheaded pine sawfly, larch looper, tussock moths and spongy moth, Japanese beetle, woolly aphids and scale insects.
• Diseases: needle cast, needle rust, cankers and gray mold.
• Growing conditions: it handles air pollution, shade and drought poorly and declines in summers that are too hot and humid.

A tree in a sunny spot, watered regularly and grown in well-drained soil resists these problems better.

Toxicity

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