Select a seedling from a Japanese maple variety that has small leaves, attractive bark and a branching habit that suggests an interesting form. Dwarf varieties are ideal for bonsai because their growth is easier to control and the foliage will remain more proportional to the trunk size. Lace-leaf or bamboo Japanese maples also are good choices because of their interesting foliage.
Prune the Japanese maple to remove opposite branches. Cut back any long branches to limit the tree's size. The two lowest branches should face in opposite directions. The third branch should extend toward the rear of the plant.
Cut back the root ball by one third to one half. Do not disturb the main roots near the trunk of the tree or the threadlike feeder roots growing from them.
Plant the tree in a container to develop the tree's root system and girth. Wrap the tree loosely with annealed copper wire in a spiral up the trunk and around the main branches and gently bend the tree into shape. Rewire the tree as its girth expands to avoid scarring the bark. Leave your tree in the smaller container for a year before transplanting.
Select a flat, shallow container for your bonsai. In bonsai tradition, a bright Japanese maple with red foliage traditionally requires an unglazed container colored with muted greens or blues. Cover the bottom of the container with galvanized wire screening.
Create a potting soil for your bonsai tree by sifting dry garden loam, clay subsoil and peat moss separately into distinct mixtures through three sieves: a coarse sieve with 4 wires per inch, a medium sieve with 8 wires per inch and a fine sieve with 14 wires per inch. Discard any particles that pass through the fine sieve.
Place a drainage layer of soil on the bottom of your tray using 1 1/2 part coarse sand and 1/2 part loam, 1/2 part clay and 1/2 part peat moss from the coarse sieve.
Prune your Japanese maple one week before transplanting by removing most of the new top growth. Prune the roots as you transplant the tree. Cut the roots back to the horizontal members and feeder roots. Work quickly so the roots do not dry out.
Place the tree onto the drainage layer of the soil so the trunk is slightly off-center. Wire the tree to the tray through the holes at the bottom of the tray with insulated electrical wire. Add rocks or any large features.
Hold the tree in place with one hand. Add soil from the medium sieve with the other. Work the soil around the roots to remove air pockets with a chopstick. Then add a layer of fine soil over the top of the roots. Cover the planting with moss. Saturate the soil with water and place the bonsai outdoors in a shady, protected spot. Repot a young Japanese maple twice yearly. Mature Japanese maples that do not grow quickly will only need repotting every three to five years.
Move your tree into a location where it will receive three to five hours of sunlight daily with afternoon shade.
Water your maple daily with a water dropper. Use a water-soluble (20-20-20) fertilizer once every two weeks according to package directions in spring and summer. Do not fertilize in fall and winter.
Prune bonsai trees to direct the growth of the tree. Bonsai trees require constant pruning to help shape the form. Trim upper branches by removing part of them and leaving only one or two leaves to allow light to reach lower branches. This will encourage closer set twigs on the crown, which is a characteristic of mature trees.
Trim a tree's leader back and wire the tree to make a new leader from one of the shoots that emerges as a result. Repeat this process every few years to develop a strong, tapering trunk. Control the direction new branches go by pruning just ahead of buds that face the direction you desire.