Crape myrtle bonsai

Placement

Give crape myrtle full sun. Direct light encourages flowering and helps prevent fungal diseases and insect attacks; in shade it flowers poorly and its leaves grow larger, which spoils the bonsai’s proportions. It also likes humid air. In warm regions it can stay outdoors all year.

In temperate climates, winter in a pot is the tricky part: the tree is not fully hardy in a container. Bring it in as soon as nights could drop below 36–37 °F, into a cool, lightly heated room where the temperature falls at night, around 45–54 °F. This cool rest lets it shed its leaves and go dormant. Keep temperature and light as steady as possible: changing conditions lead to soft, sappy growth. A tray of moist gravel helps keep the air humid. A tree that enjoyed a hot summer copes better with winter.

Powdery mildew is the most common problem: white to grayish powdery patches on leaves, flowers and young shoots, which become distorted. It thrives in shade, stagnant air, and humid nights followed by mild days. Full sun and good air circulation prevent it; if it appears, treat with a suitable fungicide. Leaf spot can also strip the tree in late summer during warm, wet weather. The crape myrtle aphid, a small yellowish green insect with black spots, goes through several generations a season: leaves yellow, young shoots become distorted and get coated in sticky honeydew that draws ants and wasps. Knock aphids off with a jet of water or treat with insecticidal soap or horticultural oil; ladybugs and lacewings help keep them in check. Their honeydew feeds sooty mold, a black, powdery coating that looks bad but does no direct harm and fades once the insects are under control. In midsummer, beetles can also chew the leaves between the veins: pick them off by hand. Indoors, watch for mealybugs, spider mites and whiteflies. The same symptom, such as yellow leaves, can have several causes.

Soil mix

Use a free-draining, well-aerated mix that is richer than for most bonsai: about two-fifths organic matter to three-fifths mineral components.

Watering

While growing and flowering, crape myrtle uses a lot of water: the root ball should stay evenly moist at all times, never soggy. Don’t water on a schedule: check the soil every day and water thoroughly, until water runs out the bottom, as soon as the surface starts to dry. In winter, while dormant, cut back sharply on watering without letting the root ball dry out.

Fertilizer: apply liquid fertilizer every two weeks from spring to fall, or use a solid organic fertilizer. Do not feed during winter dormancy.

Pruning

Crape myrtle flowers at the tips of the current year’s shoots, so every cut should take future flowers into account.

• Maintenance pruning: let new shoots extend, then cut them back to one or two pairs of leaves in late spring. Avoid pruning in summer, because flower buds form on the growth that starts in early summer.
• After flowering: pruning in late summer or fall encourages buds for the following year.
• Structural pruning: hard cuts thicken the trunk and increase branching, but sacrifice flowering for a while.

Styles: informal upright and cascade suit it; it is mostly grown in medium to large sizes.

Propagation: sow seed in spring at around 50–55 °F; take softwood cuttings in late spring, or semi-ripe cuttings in summer with bottom heat.

Wiring

Crape myrtle produces many upright shoots that need to be wired downward to build branches. Do it early: wiring is easy while shoots are less than three or four years old, after which the wood becomes very brittle and snaps easily. You can wire from spring to fall, but late winter, when the tree is leafless, gives the best view of the branches.

Its smooth bark is one of its assets: wrap the wire in paper or tape before coiling it, choose wire about one-third as thick as the branch, applied at roughly 45°, and remove it in time, cutting it at every turn. To position older, brittle branches, use guy wires rather than coiled wire.

Repotting

Repot every two to three years in early spring, as new growth starts and nights approach 50 °F; a young, vigorous tree can be repotted every year. Check the root ball first: roots circling the pot tell you it is time. Cut away no more than about a third of the roots. Cover the drainage holes with mesh, work the mix between the roots with a chopstick, then protect the tree from temperature extremes and wind for a few weeks, without fertilizer.

The crape myrtle profile covers growing it in the garden and in containers.