Acer palmatum Thunb. ex A.E.Murray
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Acer palmatum, commonly known as Japanese Maple, is a large shrub or small tree that is ideal for small gardens or front gardens.
Acer palmatum was already described by Carl Peter Thunberg but it was not until 1784 that the name was validly published by Edouard Muret.
Acer palmatum is a species in the genus Acer which contains approximately 230 to 296 species and belongs to the family of the Aceraceae (Maple Family). The type species of the genus is Acer pseudoplatanus.
Japanese Maples grow as arborescent large shrubs or small trees that usually are multi-stemmed. They are slow-growing with an annual growth of approximately 20 to 30 cm both in height and width. The shrubs/trees have a picturesque habit and reach 5 to 8 metres in height and width. The crown is rounded, becoming more umbrella-like in age.
- A lot of Acer palmatum cultivars differs greatly in growth.
Wood and Bark
Young shoots are thin, the bark of the species is olive-green to dark brown and smooth. Older branches are grey.
- Some cultivars have differently coloured young shoots.
Acer palmatum is a deciduous plant with alternate, simple leaves. The leaves are fresh-green turning brilliant orange to red in autumn. The leaves of the species are fan-shaped (= naming). They have five to seven (rarely nine) lobes and are deeply incised. The lobes are long acuminate.
- The various cultivars are mainly defined by the very varying form, colour and markings of the leaves.
Flowers and Fruit
The five-petaled flowers are 6 to 8 mm wide and are arranged in corymbs. They are dark red and appear in May.
The reddish fruits are schizocarps, the "typical" maple fruit that fall off as two winged nuts.
Acer palmatum has shallow roots with a large portion of fine roots near the surface. The roots love cool and moist (not wet!) conditions so the rooting zone should be covered if planted in a sunny and dry position.
The Japanese Maple prefers a sunny to half shady site and can withstand temperatures down to -23Âº C (USDA zone 6). If the soil is very sandy the plants should be put in a slightyl shady position with protection from strong wind.
The soil should be moderately moist to moist, sandy-humous, and well-draining. Acer palmatum likes sandy and humous loam but is only slightly tolerant of limy conditions. The pH-value should be between 4,5-5 and 7,0.
Acer palmatum is especially well suited for smaller gardens due to its moderate size and the ornamental effect of its brilliant autumn colour and often picturesque growth. The plants can be used as solitaires, for example in front of dark conifers, or in combination with other shrubs, perennials and grasses. They are good planting companions for Rhododendron, largely sharing the same preferences for soil and nicely contrasting in shape. Many cultivars are suited as potted plants where the autumn colour is especially brillant. The filigree cultivars should be put close to squares or seets where they will be better noticed. Wide and low-growing cultivars are suited for rockeries or next to water basins.
Furthermore suited for moorland gardens and for rooftop gardens, as well as suited as cemetery plant and as container plant.
Acer palmatum and its cultivars are popular in the art of growing bonsai trees because they are naturally slow-growing, very often picturesque in growth and easy to put into shape.
- Choosing the right site is important: it should be moist and well-drained, for example on top of a small mount. The plants will mature better and be less susceptibel to winter damage.
- Fertilization: fertilize with a slow-release fertilizer in Mid-April. Do not over-fertilize, very moderate nutrition results in better autumn colour.
- Watering in summer: keep the root area moist but never wet and the foliage dry! Use shade plants or mulch to guard the root area from drying out.
- Prunning: corrective pruning, if necessary, only in summer. Cutting the plants in autumn or winter might result in them getting a fungal disease. Avoid transplanting.
- Winter protection is not necessary. Young shoots my be protected from late frosts in May by slightly shading them.
Pests and Diseases
- Honeydew, galls and distorted leaves are a sign for an infestation with aphids. On larger shrubs just leave them to the birds, but use an insecticide on less vigorous specimens. Adding a few drops of washing-up liquid leads to a more even distribution thus improving the effectiveness.
- Fine webs on the plants indicate an infestation with red spider mites. These sap-sucking insects are secondary parasites that may occur if the position is too hot and dry or the plants are undernourished. There are systemic agents to treat and infestation. Importan: never apply pesticides in the sun or on heated leaves.
- Plants are susceptible to twig-dieback caused by Verticillium, especially on soil that is too wet. If the twig start to wilt during growth they immediately cut back into the healthy wood. Prevent by choosing the right position.
Varities and Cultivars
There are over 300 cultivars. A small selection:
- common 'standard cultivars' are:
- A. palmatum 'Atropurpureum' - tree-like habit, smaller than the species (150-200cm), dark-red leaves with bright red autumn colour
- A. palmatum 'Dissectum' - low to hemispheric growth, slow-growing (50-100 cm), lime green, dissected leaves, orange to yellow autumn colour
- A. palmatum 'Ornatum' ('Dissectum Atropurpureum')- like 'Dissectum' but more vigorous, leaves reddish brown, later bronze-green
(stated heights after 10 to 15 years)
- 'expanded range':
- 'Ariadne' - slow-growing, leaves variagated in pink, white or crimson, hemispheric growth (-250 )cm, autumn colour orange-rose-red
- 'Beni shishi henge' - upright growth, leaves with cream yellow margins
- 'Butterfly' - upright, slow-growing (100-150 cm), leaf markings and margins cream white to pink
- 'Bloodgood' - like 'Atropurpureum' but slightly smaller (150-200 cm), leaves with five (to 7) lobes, constantly crimson red, scarlet autumn colour
- 'Osakazuki' ('Taihai') - up to 3 metres, large 7-lobate leaves, expressive autumn colour
- 'Crippsii' - slow-growing dwarf cultivar (120-150 cm), starlike leaves with sometimes involute leaves, leaves lime green, yellow in autumn
- 'Fireglow' - compact growth (100-150 cm), bright red leaves that turn orange-red in autumn
- 'Green Trompenburg' - deeply dissected, glossy green leaves, upright growth (300 metres), yellwo autumn colour
- 'Kamagata' - dwarf cultivar (50-100 cm), densely branched, small and deeply dissected leaves, autumn colour yellow to orange-red
- 'Katsura' - upright growth (150-250 cm), young leaves yellow-orange, early orange-red autumn colour
- 'Koriba' - arborescent shrub (150-250 cm) - small bronze-orange leaves that turn a brownish-red crimson, bright orange autumn colour
- 'Koto no ito' - delicate upright growth (100-150 cm), deeply dissected lime green leaves
- 'Kotohime' - dwar cultivar (50-100 cm), rounded to columnar growth, young leaves bright pink to orange-red, small leaves with widely dentate margins, orange autumn colour
- Walter Erhardt, Erich GÃ¶tz, Nils BÃ¶deker, Siegmund Seybold: Der groÃe Zander. Eugen Ulmer KG, Stuttgart 2008, ISBN 978-3-8001-5406-7. (Ger.)
- Christoper Brickell (Editor-in-chief): RHS A-Z Encyclopedia of Garden Plants. Third edition. Dorling Kindersley, London 2003, ISBN 0-7513-3738-2.