The first bonsai appeared in China more than a 1,000 years ago when gardeners grew large-size trees in small containers. Today, bonsai has evolved into an art form that involves miniaturising trees by confining their roots. Specimen trees such as Japanese maple typically are kept outdoors. But with a tropical tree such as an orange you can carry on the practice of bonsai in the home.
Grow a miniature orange tree that is already known for performing well indoors. Calamondin oranges are good specimens for bonsai culture. The trees have been used as bonsai by many bonsai artists. It is notable for producing blossoms year-round. Calamondin bonsai orange trees will produce full-size fruit.
Remove the calamondin from its container. Wash the soil away from the root system. Gently untangle the roots so that they hang loosely from the trunk of the tree. Prune away opposite branches, and cut back long branches so they are the same length as the shorter branches. Make a cut just in front of a bud. Remove one-third to one-half of the roots, using a bypass pruner.
Place the orange tree in a standard garden container with potting soil to let it grow and develop new roots. Wrap the trunk and branches loosely from the soil line to the tip of the branches with copper bonsai wire. Use anti-clockwise turns, keeping the wrapping loose so that the wire does not cut into the tree's bark. Bend the wire so that the tree forms the desired shape. If the tree won't fully bend, bend the wire as far as possible without breaking the tree. Bend the wire again once the tree heals into this shape. Citrus trees have a naturally compact, ball-shaped canopy and upright growth. Remove branches or wire the tree to maintain this form. Allow the tree to grow for a year before transplanting it to the bonsai tray.
Prune most of the new top growth from the calamondin orange tree one week before transplanting it into its new bonsai tray.
Prepare a container for the bonsai tree. Most bonsai artists prefer a shallow tray to confine the roots of their tree. Cover the bottom of the tray with galvanised wire screening. Sift the soil into grades by passing it through increasingly smaller wire screens. Cover the screen in the bottom of the tray with the largest grade of soil, which is soil that is caught when passed through a wire screen with three strands per 2.5 cm (1 inch). Add a layer of peat moss followed by coarse soil that is trapped by a wire screen with eight strands of wire per 2.5 cm (1 inch).
Remove the calamondin citrus from the container. Rinse the soil from the root ball. Gently untangle the roots so that the structure of the root system is visible. Cut the roots back to the main horizontal roots and the feeder roots. Work quickly so that the roots do not dry out.
Spread the roots over the potting soil on the tray. Position the plant so that it looks attractive. Pass insulated electrical wire over the roots and through holes in the bottom of the tray. Twist the wire around the roots to anchor the tree. Do not make the wire so tight that it cuts into the bark of the tree.
Work soil into the air pockets between the roots of the calamondin orange tree, using toothpicks. Add a layer of soil over the roots that is trapped by a screen with 14 wires per 2.5 cm (1 inch). Cover this soil with a layer of moss. Saturate the soil with water and leave in a sunny windowsill out of direct sunlight until new growth appears.
Remove the bonsai wire when the tree holds its shape on its own.