Pruning

For Japanese Maple bonsai, in the spring pinch back the new shoots to the first pair of leaves as early as possible.  This will help create shorter internodes and develop ramification.  On younger or weaker Japanese Maple bonsai, however, allow the new shoots in spring to elongate until they harden off in May.  This will allow for hormonal exchange to take place within the plant and strengthen the overall health.

Japanese Maples do not respond well to defoliation or partial defoliation, as they will likely produce an unbalanced second flush of growth and may experience some twig dieback.  Rather than defoliation, it is best to perform either one leaf removal in each pair and/or leaf cutting in May.  Leaf cutting involves cutting each remaining leaf on the external canopy of the tree in half to allow more light to penetrate to the interior, weaker areas of the tree.

For Trident Maple Bonsai, allow the new shoots to elongate in spring until the new growth hardens off sometime in May.  At that point, it is possible to cut the shoots back to two leaves and then perform partial outer canopy defoliation, removing 80-90% of the leaves from the outer canopy of the tree.  This will induce a second flush of growth, which will be smaller in size and produce more branch ramification in a single growing season.

For a more in-depth look at pruning techniques, please consider joining our online bonsai learning platform Bonsai-U!

Wiring and Styling

Wiring and styling maple bonsai is best done either in the winter, just after the leaves have fallen or in late spring, just after the new leaves have hardened off.  Keep in mind that if you wire in winter, it is best to avoid heavily bending branches, as this can cause dieback in the subsequent spring season.  Utilize aluminum wire for these species, as it is softer on the bark and will cause less damage.  Wire will likely need to be removed within 1 to 2 months after application to avoid biting into the branches.

Repotting

Repotting maple bonsai is best done in early Spring just as the buds begin to swell.  This usually happens sometime in March in the northern hemisphere.  When repotting, it is okay to remove all of the original soil, as these species are quite strong and respond well to this treatment.  Also, it is possible to cut up to 50% of the roots without subsequently weakening these species.

Use a slightly more water-retentive soil medium, such as Aoki Blend or a mixture of akadama, lava rock and pumice in a ratio of 2:1:1.  The soil particle size should be approximately 3/16 inch (4mm) for medium and large trees, and slightly small for shohin size bonsai.

Watering

Japanese Maple and Trident Maple bonsai do well if kept slightly moist.  As a general guideline, check the water twice per day during the growing season from early Spring through late Fall.  Most maple bonsai will need to be watered at least once per day, and sometimes twice per day, during this period.  Water as the soil surface becomes dry and avoid misting the foliage, as this can lead to burn and disease.  In the winter months, check once per day and water as needed, which could be as little as once every 5-7 days depending on the climate and the individual maple bonsai.

Fertilization

Fertilizing maple bonsai will be dependent on the stage of development of the tree.  For example, younger trees are best fertilized with a high-nitrogen synthetic fertilizer to rapidly increase their size and vigor, starting from the early spring through the end of the growing season.  Older, more refined maple bonsai should be fertilized with a milder organic fertilizer with a lower nitrogen value.  This fertilizer should only be applied after the first set (or second set) of growth has completely hardened off so as to avoid producing overly large leaves.

Placement

Maple bonsai trees do best if kept in full sun in the spring as the new growth is emerging.  This helps produce more vigorous growth as well as smaller leaves.  As the temperatures heat up in summer, though, place them in partial shade.  At Eisei-en, we place our maple bonsai under 30-40% shade cloth starting in early June through late September.

Pests/Diseases

Maple bonsai are susceptible to a number of pests including aphids and cottony scale.  The most common diseases that affect these species are verticillium and powdery mildew.  For a comprehensive understanding of what fungicides and pesticides to use on your maple bonsai, please join Bonsai-U!