Japanese maples (Acer palmatum) are small, deciduous trees grown for their graceful habit, coloured stems or beautiful foliage. Their amazing foliage which may be deeply dissected, gives exceptional autumn colour. Many Japanese acers grow extremely slowly and are perfect in a smaller garden, or can be grown successfully in a large container.
Most cultivars are small slow-growing trees. Their ideal soil ph would be just on the acidic side of neutral at about 6.5ph, they are happy in a variety of soils, as long as you don’t let them dry out too much, or let them get water-logged. Japanese maples grow best in a sheltered position although red and purple leaved cultivars need some sun to develop fully their dark colouring. Variegated Japanese maples need partial shade to prevent the afternoon sun scorching the foliage. Green-leaved forms tolerate full sun but are best in dappled shade as very bright conditions can sometimes cause scorch.
Most acers have shallow fibrous root systems that resent competition from other plants. They need to be planted at the same level as they were in the pot and mulched every couple of years with well-rotted garden compost or well- rotted manure ensuring that the mulch does not come into contact with the stem of the plant.
When planted in a container use 60-70% multipurpose compost, mixed with a loam-based compost such as John Innes No 2 and some perlite to improve aeration as well as drainage. Keep the compost evenly moist, but not soaking wet and feed in spring and early summer with a slow-release fertiliser or liquid feed. If the compost dries out the edges of the leaves will scorch. A container grown plant will need repotting into a slightly bigger container every couple of years, during April or September. Choose moisture-retaining glazed ceramic containers rather than terracotta, which dries out quickly. Because the roots of maples in pots may freeze during the winter, wrap containers in bubble wrap and secure it with garden twine.
Acer palmatum is best pruned from November to January when dormant , as maples will bleed sap from pruning cuts at other times and this will weaken the tree. Only remove badly-placed or crossing shoots to encourage a good framework as the best shaped maples develop naturally. If you do have to reduce height or width, follow long branches back to a side branch and prune it out at this point. This shouldn’t need doing on prostrate- growing trees as they should be allowed to spread naturally for best effect.
Top Japanese Acers
Acer palmatum ‘Sango-kaku’ (coral-barked maple) is a large deciduous shrub or small tree to 6m (19’), with coral-red young branches bearing 5-lobed leaves which open pinkish-yellow, becoming green in summer and yellow in autumn. Flowers are small and reddish. Height 4-8m (13’-26’), spread 2.5-4m (8’-13’).
#Acer palmatum ‘Osakazuki’ is a large deciduous shrub of rounded habit. Leaves are relatively large, 7-lobed, green but turning to brilliant orange-scarlet in autumn. Flowers and fruits are small and red. Height and spread 2.5-4m (8’-13’).
Acer palmatum ‘Atropurpureum’ is a slow-growing acer, bearing deeply lobed, red-purple leaves that turn a brilliant scarlet in autumn before falling. It makes a beautiful small tree, and the deepest purple colouring results from a spot with more light, while the foliage will be greener in low light areas. For best results, grow Acer palmatum ‘Atropurpureum’ in moist but well-drained soil in partial shade. Protect it from the harshest winds, which may cause leaf scorch. Height 8m(13’), spread 10m (32’).
Acer palmatum var. Dissectum ‘Seiryu’ has an unusual upright habit and beautiful lobed leaves which turn crimson in autumn. For best results grow ‘Seiryu’ in moist but well-drained soil in partial shade. Protect it from the harshest winds, which may cause leaf scorch. Height 7m (22’), spread 3m (10’).
Acer palmatum var. Dissectum ‘Garnet’ has deep purple finely toothed leaves that turn orange in autumn. Ideal for patio containers or in the border as their roots are compact and non-invasive. Will perform best in partial shade but can tolerate full sun, needing extra moisture in summer if in a very dry location. Height 2-3m (7’-9’), spread 2m (7’).
Acer palmatum dissectum ‘Viridis’ is a beautiful low growing, weeping deciduous Acer that forms a mound habit. The feathery foliage is a bright lime green throughout the spring and summer before turning shades of red, orange and gold in the autumn. Acid soil will ensure the best autumn colour although lime can be tolerated. Prefers partial shade, but can tolerate full sun. Ideal for planters or a focal point in a border. Height 2-2.5m (7’-8’), spread 1.5-2m (5’ 7’).
Acer palmatum ‘Katsura’ is a deciduous shrub of erect growth with 5-7 lobed leaves, yellowish-orange margined with pink in spring becoming green in summer and turning bright orange in autumn. Height and spread 2.5-4m (7’-13’).
Acer palmatum ‘Butterfly’ is an upright shrub or small tree with 5-7 lobed leaves. It has irregularly margined leaves with creamy-white and often tinged pink and occasionally small red flowers in the spring. Height 2.5-4m (7’-13’), spread 1.1.5m (3’-5’).