Japanese maple, Acer japonicum

The Japanese maple, botanically called Acer japonicum, is considered a splendid specimen among the maple plants and is the epitome of beauty and vitality. The short-stemmed small tree has been cultivated in Japan for hundreds of years. The color highlight comes with the beginning of autumn, when the leaves of the maple turn a breathtakingly bright orange to fiery red. Many varieties also have a lot to offer visually in spring and summer.

care

Acer japonicum does not place particularly high demands on its gardener. With proper care, the wood can live well over a hundred years. However, a suitable location and optimal soil conditions are a prerequisite for this.

Location

The Japanese maple does not grow very quickly and most varieties do not grow taller than three meters. Some cultivated forms remain even smaller. Therefore, the wood is also ideal for smaller gardens. In nature, the Japanese maple grows sheltered from the wind on the edge of the forest in the light shade of neighboring trees. The Acer japonicum also prefers these conditions in the garden. The shrub or small tree definitely deserves a prominent place in the garden and looks best in isolation.

• Light requirement: sunny to partially shaded
• older trees can withstand full sun if the soil conditions are good
• otherwise a bit more shady in midsummer
• in the shelter of a house wall or a large tree
• preferably morning sun or afternoon sun
• as sheltered from the wind as possible
• the finer the leaves, the less wind they can tolerate

floor

The Japanese maple prefers deep, permeable soils without lime and with a weakly acidic or neutral pH value. Sandy-loamy substrates with humus content are favorable.

• sandy loamy or gritty loamy
• well permeable to water
• profound
• humus
• pH value: slightly acidic or neutral (4.5 to 7)
• most varieties are not lime-tolerant

Soil preparation

The most common causes of damage or poor growth are poor soil preparation and improper planting of maple trees. The tree benefits lifelong from good soil preparation.

Heavy, poorly drained soils

Heavy, impermeable soils are not a good prerequisite for the healthy growth of Acer japonicum. Waterlogging and poor ventilation can lead to root rot and diseases.

• Dig triple the bale depth and double the width
• Create drainage from gravel or chippings
• Incorporate 20 to 30% organic material such as compost or humus
• do not use mulch or fresh bark
• Put the bale about 2 to 4 centimeters higher
• Pour the hill up to the edge of the ball

Sandy soils

In very permeable soils, the planting hole should not be dug deeper than the root ball. For this, it is preferably excavated many times wider.

• Planting hole: depth of the root ball, five times the width
• Fill in organic material
• ripe compost or humus
• do not plant any deeper than before

plants

Take great care when planting, because the Japanese maple can live well over a hundred years. So it is worthwhile to choose a particularly favorable location and prepare the planting accordingly. If mistakes are made here, this often only becomes apparent after years and a correction is then often no longer possible.

• Time: spring or autumn
• Water the plant well before planting
• put it in a bucket of water for at least 15 minutes
• Carefully remove from the pot
• Slightly loosen the outer root network
• Match the planting hole and planting depth to the nature of the soil
• Fill up with substrate and step lightly
• do not add any additional fertilizer
• Protect the surface from evaporation with mulch
• Always keep slightly moist, but not wet, in the first vegetation phase

Planting time

If you plant a maple tree in autumn, the tree will benefit from the new root growth that occurs during the dormant period. Unlike the shoots, the roots of maple trees continue to grow steadily in autumn and the early winter months, provided the temperatures are not below freezing point. When planting in spring, you should be very careful not to accidentally snap off or destroy shoots that have recently budded.

Bucket culture

With good care, dwarf varieties can get along well with a plant pot for years. In the long run, however, the Japanese maple should be planted outdoors.

• Planter: maximally double the ball size
• must have drainage holes in the bottom
• Substrate: high quality multi-purpose compost with sand or grit
• alternatively good potted plant soil
• first create a drainage layer
• grit, small pebbles, expanded clay or lava granules are suitable for this
• Tear the root network slightly by hand at the edge
• Place the pot on small feet so that the water can drain off easily

If planters are too generously dimensioned, there is a risk that the soil will become very saturated with water and that root rot will develop. The tub should therefore have a maximum of 1.5 times the diameter of the root ball.

to water

Acer japonicum is one of the shallow roots and therefore prefers a moist, fresh soil. Regular watering on hot days and when it is dry is therefore essential. Especially in the first few years after planting and with potted plants, it is often necessary to check whether the substrate still contains sufficient moisture. It is only poured when the upper layer of soil is already dry to the touch. The root ball of the maple must never dry out completely. Also make sure that no waterlogging forms. The tree reacts very sensitively to moisture at the roots. It is preferably poured in the early morning hours or in the evening.

Fertilize

Of course everyone wants a bigger maple tree, but too much fertilizer would be the wrong way to make the wood grow quickly. In fact, most Japanese maples require little or no additional fertilizer for healthy growth. If the trees are treated with fertilizer as soon as they are planted, this often leads to diseases and the death of the shoots. That is why freshly planted young trees are not fertilized at all until the second or third vegetation period.

• give mineral fertilizers only in tiny doses
• organic slow release fertilizers are better
• also more mature compost is suitable as a nutrient supplier
• Outdoor plants: one-time fertilization in April to May
• Container plants: several times in the growth phase
• use special fertilizers for Japanese maple
• Do not fertilize any more from the beginning of August

Work some patent potash into the soil in early fall. This way you prepare your tree perfectly for winter.

Repot

Over time, the substrate in the planter tends to thicken. This means that nutrients and water can no longer be sufficiently absorbed through the roots. By repotting in fresh, loose substrate and possibly a somewhat larger planter, deficiency symptoms can be prevented.

• When: every two to three years in early March
• Repot young plants more often
• Slightly loosen the root ball

In old trees, the roots can be cut up to 20% if a larger pot is no longer possible. In this case, however, it is better to wait until the end of April or the beginning of May to repot. This is because the roots store energy in the form of sugar and starch over the winter, which the plant needs to sprout the leaves. After sprouting, part of the roots can be removed without damaging the plant.

Cut

A pruning is seldom necessary with the naturally very shapely growth with broad, richly branched crown of the Acer japonicum. Cutting Japanese maples is also a tricky business. The wood does not always react positively to shaped cuts. In order to prevent a weakening of the plant through excessive pruning, the shoots should therefore only be removed as part of minor corrections. These are usually done in late winter before new growth. Since the trees are in the sap very quickly in spring, it is not advisable to cut them at a later point in time. In this case, there is a risk that the tree will bleed for a long time or become infected with fungal pathogens.

• Time: February to early March
• only necessary every two to three years
• only cut on rain-free days
• remove all sick and dead branches
• cut one of two intersecting branches
• cut off inward-growing shoots
• close larger wounds with tree wax

In early summer it is checked again whether all shoots have survived the winter undamaged. Frozen and dried up shoots on which no foliage has formed by the beginning of June are cut back into the healthy wood.

Note: Always work with clean and sharp cutting tools.

Overwinter

Unfortunately, the Japanese maple is not quite so frost-resistant that it can be overwintered outdoors in cold regions without protection. The frost resistance depends not only on the variety, but also on the age of the wood and the location.

Outdoor plants:

In general, a Japanese maple can withstand a maximum of -10 degrees. Young trees do not yet achieve this winter hardiness. You will need a few years to withstand the frozen ground and the combination of cold and sun. Therefore, especially younger plants in cold regions should be given winter protection.

• sheltered location
• Cover the root area with straw, leaves or fine brushwood
• Layer thickness: at least 10 cm
• possibly cover with a coconut mat as a windbreak
• Wrap the trunk with a fleece, a straw or coconut mat
• Protect from strong sunlight during frosts

Older potted plants:

With container plants, you have to ensure that the soil in the pot does not freeze through in winter. Since the Japanese maple reacts very sensitively to a wet root ball, especially in winter, the appropriate winter protection begins with the planting. A humus-rich, well-drained substrate and drainage in the pot ensure good drainage of the water. The last fertilization is done in August with patent potash to improve winter hardiness. So that the young shoots can mature before winter, there is no more fertilization from mid-August.

• Install protected from mid-September
• Wrap the pot in several layers with bubble wrap, brushwood mats or fleece
• Do not close the drainage holes in the floor
• Place the vessel on the styrofoam plate
• Sprinkle a thick layer of straw or leaves on the substrate surface
• Water occasionally in frost-free weather

Young potted plants:

A Japanese maple that is still very young or that is grown in a very small pot is best placed in a cold house over the winter. But never bring the sapling into the warm apartment. The maple absolutely needs several months of winter rest. In the heated apartment there is a risk that the tree will sprout again. The Acer japonicum can also stand in the dark without leaves. Cold, but frost-free quarters such as a protected garage or an unheated basement room are ideal. The cooler the location, the less water the wood requires.

• Light requirement: can also be dark
• Temperature: around 5 degrees, not over 8 degrees
• Garage or cool cellar room, unheated winter garden
• only pour in sips
• do not fertilize

If the temperatures rise again permanently above 5 degrees in spring and no more severe night frosts are to be feared, the Japanese maple can slowly get used to the outdoors again.

Multiply

In general, the Acer japonicum can be propagated from cuttings as well as from seeds. Since the wood grows very slowly, sowing the seeds requires a lot of patience until a handsome tree has grown out of it.

Cuttings

The ideal time to propagate cuttings is early summer, when the young shoots are not yet fully ripe. Soft, alternatively only slightly woody shoot tips of the mother tree are suitable.

• Cut fresh shoots about 15 cm long
• Hold the cut surface at an angle
• remove lower leaves
• a maximum of two to three leaves remain at the top
• cut very large leaves in the middle
• Dip the cut surface in rooting powder
• Put about three centimeters deep in moist potting soil
• set up bright and warm
• Avoid midday sun
• Keep the substrate slightly moist

Roots form on the cutting within about eight weeks. This can be seen from the fact that the cutting begins to grow. Now the young plant can be potted in humus-rich substrate. The young Japanese maples will not be planted until next spring.

Seeds

A cold spell is necessary for the seeds of Acer japonicum to germinate. This protective mechanism is important so that no seedlings emerge before the cold season and then freeze to death in the coming winter. Dried seeds are first soaked in water for 24 hours and then placed in a freezer bag with moist sand in the refrigerator for at least 60 days. After the cold treatment, the seeds are placed about an inch deep in a pot of moist compost. After a few weeks in a bright and warm place on the windowsill, the seeds will begin to germinate. In order to keep evaporation within limits, it has proven useful to put a freezer bag over the pot until germination has taken place.

Buy plants

Since a Japanese maple can live for over a hundred years, it is advisable to buy a young plant from a specialist store or from a tree nursery. In this case the trees are already well acclimatized to the local conditions.

Diseases

The Japanese maple is a very robust plant that rarely gets sick in a good location with suitable soil conditions. However, strong pruning or a wrong time for the cut make the wood susceptible to various diseases and can weaken the maple so much that it dies.

A drastic pruning is only necessary if the tree suffers from an infection with the dreaded Verticillium wilt. This disease is caused by fungi that are found in the soil. It causes entire branches or shoots to die off in a short time. If action is not taken quickly, the whole tree will die.

sorts

Acer japonicum 'Aconitifolium'

• tree-like shrub with a short trunk
• Growth height up to 3.5 m
• heavily incised leaves

Acer japonicum 'Green Cascade'

• slightly irregular growth
• deeply slit, red foliage
• Growth height up to a maximum of 1.5 m

Acer japonicum 'Indian Summer'

• upright growth habit
• Growth height up to 1.5 m
• yellowish, palmate leaves

Acer japonicum 'Vitifolium'

• large tree-like shrub
• Growth height up to 3 m
• large, fan-shaped leaves