Japanese larch bonsai

Placement

Larix kaempferi is a mountain tree from Japan, where it grows in temperate forests up to the tree line; on the slopes of Mount Fuji, wind and cold sometimes reduce it to dwarf forms that already look like bonsai. It is an outdoor bonsai year-round: it needs the cycle of the seasons and a true winter rest.

Give it full sun. In summer, light shade during the hottest hours keeps the needles from scorching; such scorch is often caused by a lack of water in the root ball as well. It also grows well in partial shade, but deep shade weakens it. A cool climate, close to that of its native mountains, gives shorter, denser needles; in hot, humid weather they grow longer. The tree does poorly in hot, humid summers and with air pollution.

Larch is extremely hardy: a bonsai needs no protection until temperatures drop below 5–-4 °F. Below that, move it to a cold frame or unheated shelter. A tree that spends the winter wired appears to be less cold-hardy. What bothers it most in winter is excessive rain soaking the root ball: an overhang or an open shed is enough.

Soil mix

Use a free-draining bonsai mix that is neutral or slightly acidic, for example equal parts akadama, pumice and lava rock. Add more akadama if you cannot water often, and more lava rock in a humid climate. Avoid limy soils: larch prefers rich, moist, acidic, well-drained soils and does not tolerate a root ball that stays waterlogged.

Watering

Water thoroughly as soon as the soil starts to dry, until water runs out of the drainage holes, and keep the root ball evenly moist. Check the surface and feel the weight of the pot. In full sun at the height of summer, the tree can become very thirsty: in hot weather, it can need water once or twice a day. Larch dislikes very hard water. In hard-water areas, use rainwater or give an acid-plant fertilizer every two weeks so the soil does not become too alkaline.

Fertilizer: start as soon as the buds open in spring. A high-nitrogen fertilizer first drives vigorous growth, useful on a tree in development; cut back on it for a finished tree, which should only produce fine growth. Then switch to a balanced fertilizer, liquid every week or solid organic every month. Around midsummer the tree goes into a partial rest; from late summer on, a low-nitrogen fertilizer helps it harden off before winter.

Pruning

For a conifer, larch is very vigorous and replaces a pruned shoot within a few weeks. Remove large branches in winter or early spring, before growth starts; major structural pruning is done from fall to late winter. There is no need for cut paste: its sticky resin protects wounds, and it quickly forms callus tissue.

During the growing season, shorten long shoots once they reach 4–6 in and the buds at their base become visible. Letting a shoot extend before cutting it back thickens the branch and the trunk. Remove badly placed buds before they open and, where possible, cut twigs back to two buds. On an old tree, avoid cutting back to the same points again and again: this creates unsightly knobs and ages the branch.

Larch suits almost every style, in every size, except the broom.

Wiring

Wire during winter dormancy, at the latest when the buds are about to open and the bare branches are still easy to see. Young buds fall off at the slightest knock, so work gently. Young branches are flexible and are easy to shape with wire or guy wires.

Twigs thicken very fast during the growing season. Check the wire regularly and remove it before it bites in; moderate marks grow over fairly soon, at the latest once the bark becomes flaky. To remove wire, cut it at every turn rather than unwinding it. Old branches with rough bark mark easily, so guy wires are better there. They can take several years to hold their new position and can need repeated wiring.

Repotting

Repot a young tree every two years and an old specimen every three to five years. Larch resents root disturbance: this is the trickiest step in growing it, and timing is essential. The traditional window is just before the buds turn green, although losses can still happen. Repotting in full dormancy, in the depths of winter, also gives good results; fall repotting is another option. Never repot if the root ball or roots are frozen.

Do not bare-root, do not wash the roots and do not remove more than one third of the root mass. Tease out excess old soil by hand so the roots can be gathered together and fresh soil worked into the pot. Larch roots are very frost-hardy, so a freshly repotted tree needs no special shelter.

Larch is propagated from seed in early spring, from semi-ripe cuttings in summer or hardwood cuttings in winter, although they root with difficulty, and by air layering in late spring.

Among pests, watch for aphids, especially those that leave kinked, drying needles, scale insects and mealybugs, caterpillars, and the larvae of sawflies, gall midges and bark beetles. Gray mold and needle cast can also strike. Treat with a targeted product and improve its growing conditions.