Japanese pittosporum bonsai

Placement

Pittosporum tobira is an evergreen shrub native to southern Japan and China. Its thick, glossy, dark green leaves, 2–4 in long, are clustered in whorls at the branch tips. In late spring it bears clusters of small cream flowers with an orange-blossom scent that turn yellow as they age. It tolerates wind, salt spray, heat and drought. The variegated pittosporum, with thinner white-edged leaves, is grown the same way, and the compact cultivar ‘Wheeler’s Dwarf’ has smaller leaves.

Give it full sun or part shade; it even accepts fairly heavy shade, but variegated forms prefer afternoon shade. Shelter it from prevailing cold winds. It is not very hardy: in the ground it only takes lows of about 23 °F, and a bonsai, whose roots sit in a shallow pot, freezes much sooner. In a mild climate it can stay outdoors year-round. Elsewhere, keep it outside from spring to fall, then move it before hard frosts into an unheated greenhouse, a bright porch or a cool sunroom. Without shelter, set the pot at the foot of a south-facing wall and cover the tree with frost cloth on freezing nights. It also accepts a very bright indoor spot, but not a dim room.

Soil mix

Pittosporum adapts to acidic or alkaline, sandy or clay soils, on one condition: perfect drainage. Its roots rot in soggy soil, and that rot is often fatal. Use a fast-draining bonsai mix, for example akadama, pumice and lava rock, or a blend of peat-free potting mix, coarse sand and loam-based compost. Never leave water standing in the saucer.

When the pH is too high, magnesium deficiency can appear: the oldest leaves yellow along the edges and between the veins. Yellowing can have other causes, though.

Watering

Water by observation, never on a fixed schedule. Push a finger about 0 in into the soil: when it feels barely dry, water thoroughly until water runs from the drainage holes. Rainwater is ideal; tap water is fine otherwise. The root ball should neither dry out completely nor stay soaked. A shallow pot dries quickly in hot, windy weather; in a cool spot in winter, needs drop sharply. Leaves curling inward signal a stressed tree. A few old leaves dropping from the inside of the canopy is normal; heavy leaf drop within a few weeks points instead to frost, overwatering or a dry spell.

During the growing season, use a balanced fertilizer: a low-dose liquid feed every two weeks, or a solid organic fertilizer, following the label rate. Too much produces soft shoots that are more prone to pests.

Pruning

The tree tolerates severe pruning and regrows vigorously. It has no strongly defined natural shape, which leaves plenty of freedom; the informal upright style (moyogi) suits it especially well, and removing the lower branches also lets you train it as a small multi-trunk tree. Structural pruning is done in early spring: remove dead branches first, then those that do not serve the design, using a concave cutter, whose hollow wound heals better, and seal large cuts with cut paste. Do not combine major structural pruning with repotting in the same year.

To keep the flowers, prune right after bloom: next year’s buds form on existing wood, and late pruning, in late summer or fall, removes them. Heavy, repeated pruning can even stop flowering altogether. During the growing season, cut back shoots that extend beyond the outline to make the branching denser. Disinfect your tools between cuts: cankers and dieback enter through wounds, especially bark split by cold.

Wiring

Wiring is possible at any time of year, but not on a weak or freshly repotted tree; during the growing season branches thicken quickly and need closer watching. Choose wire about one third the thickness of the branch, wrapped at roughly 45° from base to tip. Check it regularly: a branch sets within a few months, but wire can bite into the bark in as little as one to four months. Remove it by cutting at each turn rather than unwinding it. Protect thick branches with damp raffia, and use guy wires for those too stiff to bend.

Repotting

This pittosporum grows fast: yearly repotting suits it, and an older tree can wait two to three years. Do it in early spring as the buds swell, never in midsummer or winter. It tolerates severe root pruning. Untangle the root ball, cut back overlong roots and work the new mix between them with a chopstick. Water thoroughly and keep the tree out of wind and strong sun until it re-establishes.

To propagate it, layering young shoots in spring is the easiest method. Semi-hardwood cuttings 2–3 in long, taken from the current season’s shoots between late summer and early fall, root less readily: use rooting hormone, a well-drained mix and high humidity. Seeds, at 54–59 °F, germinate slowly and often have poor viability; grafting is another option.

Watch above all for cottony cushion scale, controlled with horticultural oil, as well as other scale insects, mealybugs, aphids, whiteflies and, under cover, spider mites. Sooty mold reveals aphids or scale. Pittosporum psyllid causes swollen twigs that die back. Leaf spot is kept in check with good air circulation, watering at the base and clearing fallen leaves; powdery mildew appears occasionally and usually needs no treatment. The Japanese pittosporum plant profile covers growing it in the ground and its toxicity.