Japanese maple as bonsai

Placement

Outdoors, in a bright, airy spot. Once temperatures climb above about 86 °F, move it into partial shade, especially in the afternoon, to keep the leaves from scorching. Shelter it from drying winds. It is not an indoor tree: it needs the change of seasons and winter dormancy.

The tree is hardy, even as bonsai, but in a pot the roots need protection once temperatures fall below about 14 °F, for example in a cold frame.

Soil mix

A very free-draining mix, such as akadama mixed with pumice and lava rock. Avoid very hard water: maples prefer neutral to slightly acidic conditions.

Watering

During the growing season, check it every day: watering is often daily, and several times a day in hot weather for small pots. Water thoroughly to wet the whole root ball, and never let the mix dry out completely, which quickly damages fine roots. Brown, crispy leaf edges usually mean a spell of drought, heat or wind.

Pruning

Cut new shoots back to one or two pairs of leaves. Do hard pruning in fall or early winter, never in spring, because cuts bleed sap. Protect large wounds, since maples are prone to some fungal diseases, and disinfect your tools (verticillium wilt spreads on them). Defoliation, which triggers a second flush of finer leaves, is stressful: don’t do it every year.

Wiring

Deciduous trees are easiest to wire in late winter, when they are bare. Prefer anodized aluminum wire, gentler on deciduous trees, about one third as thick as the branch. The thin bark scars quickly: during the growing season, check the wire regularly and remove it before it cuts in.

Repotting

About every two years: the roots are vigorous and soon fill the pot. Repot and root-prune in spring, before growth resumes. Afterward, keep the tree sheltered in partial shade until it recovers.