Japanese Red Maple Care Guide
Acer rubrum – also known as Swamp Maple, Soft Maple, and Water Maple, is a deciduous native of the United States and a favorite of bonsai artists because of its stunning scarlet leaves. In nature this majestic shade tree may grow upwards of 100 feet tall, though most top out between 60 and 90 feet.
The foliage is comprised of leaves that grow to about four to six inches wide and are made up of three to five pointy lobes. The leaves are green during the growing season but in fall turn to an incredible, intense red. The trunk is sturdy and thick, with gray bark that darkens with age and may crack into an irregular plating pattern. The shape is somewhat narrower at the crown than some park trees, with dense branching and foliage.
As with most maples, Red Maple does best as an outdoor bonsai. It is an extremely hardy and adaptable tree, able to adjust to extreme heat or cold. A bit of frost protection may be offered in very cold temperatures – a layer of mulch around the soil and pot will do. This tree thrives on full sun except on the hottest of summer afternoons when a bit of light shade could be provided to protect it from scorch.
Red Maple loves moisture and is adaptable to any condition in which it grows naturally, whether that is a swamp or a dry western climate. Most days a single watering will suffice but for very hot and dry days you may want to offer an afternoon watering as well. This tree is so flexible when it comes to watering that if you are going to be away for a few days you can even leave your bonsai in a container of water so that it receives consistent moisture while you are gone.
Fertilize bi-weekly with an all-purpose formula, beginning in spring just after budding commences. A dose of slow-release bone meal and blood meal in the early spring can supplement the tree's nutritional needs. Continue fertilizing through autumn.
Common Styles – slanting, informal upright, literati, multi-trunk, forest, root-over-rock, windswept, exposed root.
Large branches should be pruned at least a couple of months before spring budding occurs, in order to minimize bleeding. The Red Maple is a syrup tree and as such may experience profuse bleeding if pruned at the wrong time, which can be disastrous for a bonsai. Smaller branches can be pruned at any time.
Acer rubrum has large internodes in its natural growth setting, so encouraging ramification on a bonsai means that in early spring you may have to constantly cut shoots back once they reach four to five internodes. This will stimulate smaller, dormant buds to pop out along the branches. Remove those buds that are growing from the bottom of shoots. Leaf pruning can be used in summertime to encourage the growth of smaller leaves.
Red Maple bonsai may be wired, and it should be done late in autumn when the branches are still flexible enough – due to their sap content – to reposition without fear of breaking them. Wiring at this time also minimizes cutting in of wire because the tree is not going through a growth spurt.
The typical method of propagation for Acer rubrum is by sowing seeds. These can be obtained from the tree in spring and should be planted as soon as they are ripe. Cuttings can be used in late summer, after new growth has turned half-hard.
Red Maples can be repotted every two to three years. This bonsai has a hearty root system which can withstand aggressive pruning. At the time of repotting, roots can be gently coaxed to the surface to encourage the formation of nebari. This tree is not finicky about soil – it will grow fine in nearly any blend. It should be well-draining, and some clay content will help to restrict the size of the tree.
Insects, Pests & Diseases:
As a bonsai, Red Maple is remarkably resistant to disease and many pests. There is a possibility of attack by spider mites, aphids, leaf miners, or cottony maple scale. Mites, aphids, and leaf miners may usually be rinsed off in a jet spray from the hose.
Cottony maple scale, which look like little cotton balls underneath the branches, may need to be removed by hand or by the application of oil or rubbing alcohol. A regular insecticide routine is recommended for prevention.
Rainy weather may sometimes bring anthracnose fungus. Resembling scorch, this condition causes brown or tan areas on foliage. Fungicide may be applied in the spring in order to prevent and/or control this issue. Overall though, the Red Maple is typically a healthy tree.