Lagerstroemia
Botanical name: Lagerstroemia indica and hybrids
Common name: Crape myrtle / Crepe myrtle
Family: Lythraceae
Type: Deciduous flowering tree
Characteristics
Brilliant summer flowers (pink, red, white, lavender).
Attractive exfoliating bark, revealing mottled tan and grey tones.
Fine twigs and small leaves, making it ideal for medium to large bonsai.
Culture
The original species and early cultivars tend to be quite tender and best suited for a Mediterranean climate. Growing up in Southern California, I saw these stunning trees lining the streets. In recent years plant breeders have developed a whole range of new cultivars that are much hardier and are increasingly available across Europe. They tend to have smaller leaves than the originals, which is perfect for bonsai, and the same stunning flowers.
Even the more temperate-adapted cultivars thrive best with plenty of light and heat in the summer. I grow mine in full sun, they like plenty of water, but I've never seen them wilt even on the hottest day.
Tender below –10 °C, it's best to overwinter in a cold frame or unheated greenhouse in temperate zones as bonsai, although mine have been planted in the garden for many years. Reduce watering in winter when leafless but do not let the roots dry completely. They don't do well as indoor bonsai.
Propagation
Cuttings: Semi-ripe cuttings in early summer root easily.
Air-layering: Reliable in late spring.
Seed: Germinates readily but slower to develop bonsai trunks.
As bonsai
Well-draining but retentive mix such as akadama : pumice : lava = 2 : 1 : 1 or similar. pH neutral to slightly acidic preferred.
Mine produce an abundance of fine roots and as bonsai you might need to root prune annually in early spring.
Wire in autumn or late spring when shoots have lignified; the bark is delicate, so protect it with raffia or paper and remove before it bites in.
Most sources state that they flower on the current year's growth and you shouldn't trim shoots after early spring. I've notices that they grow new shoots in spring and then they have a pronounced pause before starting the new growth that will produce flowers. Since I've been growing my plants strongly to produce heavier trunks, I haven't tested this yet, but I suspect that it might be possible to trim back when new shoots enter this paused state and maybe still get flowers.
Left to themselves, Lagerstroemia have a tendency toward multi-trunks, although they are equally easy to grow as a single trunk. I would suggest a style that allows you to make a feature of the beautiful bark, particularly during the winter.
