Culture
Best grown in moist, organically rich, slightly acidic, well-drained soils in full sun to part shade. Grows well in sandy loams. May be grown in full sun in the northern parts of its growing range, but prefers some part afternoon shade in the southern parts (including St. Louis) of its growing range. New foliage may scorch in full sun locations in hot summers areas, particularly if soils are not kept consistently moist. Mulch helps retain soil moisture and keep roots cool. Site in locations protected from strong winds. Avoid hot and dry sites. Fertilize in spring before leaves emerge. Pruning is best kept to a minimum, but if needed should be done in late fall to mid winter. Spring or summer pruning often results in significant bleeding.
Noteworthy Characteristics
Acer palmatum, commonly called Japanese maple, is a deciduous shrub or small tree that typically grows to 10-25' (infrequently to 40') tall. It is native to Japan, Korea and China. General plant form is rounded to broad-rounded, often with low branching. Each palmate green leaf (2-5" long) has 5 or 7 but less frequently 9 pointed toothed lobes. Small reddish-purple flowers in umbels bloom in mid spring (April). The flowers are rather attractive close up, but are not particularly showy from a distance. Flowers are followed by samaras (to 3/4" long) in pairs. Samaras ripen in September-October. Fall color includes shades of yellow, red-purple and bronze. Cultivars (often grafted) are quite variable.
Genus name is the Latin name for a maple tree.
Specific epithet is in reference to the palmate nature of the leaves. Each leaf has several lobes (typically 5–7) that all originate from one point looking like an open hand with outstretched fingers.
'Osakazuki' (Amoenum Group) is a vigorous upright tree with a rounded crown that typically grows to 15-18' tall over the first 10 years, but eventually matures to as much as 20-25' tall. It is particularly noted for its vibrant crimson red fall color. Each large palmate leaf has seven serrate, moderately-cut lobes which are divided slightly more than 1/2 way to the leaf base. Leaves are green throughout the growing season until fall. Each leaf is cupped at the base, as suggested by the cultivar name (osakazuki from Japanese means leaf like a wine cup).
Problems
Potential disease problems include stem canker, leaf spots, fusarium, verticillium wilt, botrytis, anthracnose and root rots. Potential insect pests include aphids, scale, borers, bagworms, and root weevils. Mites may be troublesome. Foliage tends to leaf out early in spring and is subject to damage from late spring frosts. Chlorosis may occur in high pH soils.
Uses
Japanese maples are generally grown for their attractive foliage and shape. Specimen/accent or group around the home or yard or periphery of the border. Good sun-dappled understory tree. Woodland garden margins. Screen. Bonsai.
Best located in a sheltered location.