Acer (maple) bonsai care

The Japanese maple is a true outdoor bonsai and should be kept outdoors all year round. It grows best in a bright, airy spot with plenty of sun, but must be protected from very intense midday sun. Especially in summer, the thin leaves can burn quickly.

Morning sun and, if possible, evening sun are very suitable. During hot summer days, partial shade in the afternoon is ideal. When the temperature reaches 30 °C or higher, indirect light during the hottest hours is advisable.

Also, do not place the tree in a very windy spot permanently. Wind increases evaporation and can cause both the leaves and the bonsai soil to dry out very quickly. The Japanese maple needs its natural seasons and should therefore not be kept indoors permanently.

An Acer palmatum requires a relatively large amount of water. During the growing season, you should check the soil daily. Under normal growing conditions, this often amounts to watering about once a day. During very hot and dry days, a small bonsai pot may even require two or more waterings per day.

Therefore, 7–14+ times per week is a useful indication for the growing season, but not a fixed watering schedule. Always check the soil first.

Water as soon as the top layer of the substrate begins to dry out. The entire root ball should then be thoroughly soaked. Allow excess water to drain through the drainage holes. The roots like an evenly moist environment but should not stand in waterlogged soil for long periods.

Never let the root ball dry out completely. Japanese maples have fine roots and react quite quickly to drought. Brown, dry leaf edges can be caused by a combination of drought, heat, wind, and strong sun, among other things.

If possible, avoid using highly calcareous water. Acer palmatum prefers a neutral to slightly acidic environment. Rainwater is therefore a good option if your tap water is very hard.

In winter, when the tree has no leaves and is dormant, its water requirements decrease significantly. Keep the soil slightly moist and check it regularly.

For a Japanese maple, a solid organic bonsai fertilizeris a good foundation. Organic fertilizer releases nutrients gradually and reduces the risk of an overly strong growth spurt.

Especially with a refined, mature bonsai, it is wise not to provide excessive amounts of nitrogen. High nitrogen levels stimulate long shoots, larger leaves, and longer internodes. This is usually not what you want with a finely branched Acer.

The most important fertilizing periods are spring and autumn. For young trees where you specifically want rapid trunk and branch growth, a liquid fertilizer can additionally be used about once a week during active growth.

It is difficult to recommend a set number of times per month to feed. The frequency depends on the chosen product and its release rate. Therefore, follow the dosage for the specific product when using solid organic bonsai fertilizer.

The Japanese maple responds well to pruning, making it highly suitable for developing a fine branch structure.

You can trim young shoots back to about one or two pairs of leavesduring the growing season. This keeps the shape compact and creates more branching over time.

For mature trees, you can also pinchnew shoots. As soon as the first pair of leaves has opened, the soft growth point between these leaves can be carefully removed. This slows down longitudinal growth and helps in developing fine branching. Do this selectively: continuous pinching weakens the tree.

More caution is required for larger and thicker branches. Acers can "bleed" heavily after pruning, with sap leaking from the pruning wound. We therefore advise removing sturdy branches preferably in summer or autumn, when wound healing is rapid.

For larger branches, use a sharp concave cutter or suitable bonsai shears. Wound pastecan be applied to larger wounds to seal them and limit the risk of fungal infections.

Leaf pruning is also possible. A complete defoliation can stimulate a second, finer wave of growth, but it puts a significant strain on the tree and should not be done annually. Partial leaf pruning, where for example only very large or densely clustered leaves are removed, is considerably milder.

Acer palmatum can be shaped with bonsai wire. We recommend wiring in the spring.

Use aluminum or copper wire with a thickness sufficient to hold the branch in question without applying unnecessary pressure. Bend branches gradually and do not force them.

Check applied wiring very regularly during the growing season. A Japanese maple can grow quickly, and the relatively smooth bark can be permanently damaged when wire begins to grow into it.

For fine branches, you can also use guy wires in addition to wiring, so that you do not have to wrap as much wire directly around delicate branches.

A Japanese maple should on average be repotted about once every two years. The species produces relatively strong, fast-growing roots, which means a small bonsai pot can become filled quite quickly.

The best time is at the beginning of spring, around the moment the buds begin to swell.

Signs that repotting is necessary include a pot that is densely packed with roots, a very compact root ball, or water that has increasing difficulty draining through the substrate.

During repotting, a portion of the roots can be pruned back. Use a sharp root cutterfor this purpose and primarily remove long and thick roots, while ensuring that enough fine hair roots are preserved.

After repotting, the tree must be given the opportunity to recover. Temporarily protect it from extreme sun, drying winds, and other significant stress.

The Japanese maple requires a well-draining yet sufficiently moisture-retentive bonsai substrate.

We recommend:

• 100% Akadamaor
• 80% Akadama and 20% pumice.

The most important thing is that the substrate contains sufficient oxygen and can easily drain excess water, while at the same time enough moisture remains available for the fine roots.

Ordinary compact potting soil is therefore less suitable as a main component for a bonsai in a small pot

The Japanese maple is deciduous. In the autumn, the leaves change color and eventually fall off. This is part of the tree's natural life cycle.

The Acer must remain outdoors or overwinter in a similarly cold location during the winter, as it requires a winter dormancy. A heated living room is not suitable.

Acer palmatum is fairly frost-resistant, but a bonsai is more vulnerable than the same tree planted in open ground because the roots are only protected by a thin pot. At temperatures below approximately -10 °Cextra protection is recommended, for example in a cold greenhouse, cold frame, or other unheated sheltered space.

Furthermore, protect the bonsai from strong, drying winter winds. Also check the soil regularly during the winter: the tree uses little water, but the root ball must not be allowed to dry out completely.

The Japanese maple is generally a hardy species, but it can suffer from a few specific problems.

Aphidsoccur primarily in the spring. Regularly check young shoots and the undersides of leaves. For minor infestations, you can often remove or wash the aphids off; for more severe infestations, a suitable pesticide may be used according to the label instructions.

A much more serious problem is Verticillium wilt. This is a fungal infection that can cause parts of the tree or, ultimately, the entire tree to die. In a fresh cross-section, dark to black discolorations may be visible in the wood. There is no effective treatment.

Furthermore, Verticillium can be transmitted via pruning tools. If you suspect the disease, tools should therefore be thoroughly cleaned and disinfected before you use them on another tree.

In addition, the species can be susceptible to issues such as leaf spot/scorch, mites, and certain scale insects. Incidentally, not every brown leaf edge means the tree is diseased: overly bright sun, dry soil, or strong wind can cause similar damage.