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What is “Bonsai?”

The cultivation of bonsai began more than two thousand years ago in China. An emperor of the Han Dynasty created a representation of his kingdom in miniature. Landscapes were called penjing or pen-sai. The earliest documented proof of penjing is a painting found in the tomb of Prince Zhang Huai of the Tang Dynasty, who died in the year 206 A.D. When the Japanese invaded China in the nineteenth century, they were so fascinated by the miniature trees in pots that they began to practice the art in Japan. The Japanese word for ‘tree in a pot’ is “bonsai” (pronounced ‘bone-sigh’). Bonsai cultivation in the United States became prominent after the second World War.

Bonsai is the miniaturization of trees and shrubs that occurs by regular pruning of the roots and branches. A mature look is desired; therefore the tree might be planted in the ground to help the diameter of the trunk reach a desired thickness before placing in a carefully selected pot that will show the tree off in a harmonious way. Further enhancement to achieve a mature look is done by altering the shape of the trunk and branches. Wiring the trunk and branches is the preferred technique, but there are other ways of achieving shape.

Out Door vs. Indoor

Outdoor Bonsai
Outdoor bonsai are those trees and shrubs that are accustomed to living in subtropical, temperate, and cold climates. All conifers, such as junipers, pines, firs, spruce, etc., almost all deciduous (those that drop their leaves part of the year), and evergreens such as holly, rhododendron, camellia, etc. should spend all of their time outdoors. In cold climates, bonsai must be protected from cold winds and bitter cold temperatures by being stored in a cold frame, greenhouse or unheated garage. It is common to see junipers sold as indoor bonsai, but this is a misconception. Some books even suggest that one can bring an outdoor bonsai into the house for a day or so, but it is not recommended unless one is displaying the tree in a show, which happens infrequently.

Indoor Bonsai
A few semi-tropical and all tropical species of trees and shrubs that live in the warm climate regions of the world are suitable for indoor bonsai. Figs, aralias, sheffleras, serissas, and miniature boxwood are good candidates. It is possible to keep the trees indoors year round if they are placed by windows that give adequate light or have supplemental lighting over them. Extra lighting is highly recommended if growing indoor bonsai in places that receive less than twelve hours of daylight. One should provide as close to the trees’ original environmental qualities as one can. Indoor bonsai are sensitive to cold drafts and should never be place on top of fireplace mantels or near heat sources. All indoor bonsai will enjoy the warmest part of the summer in an outdoor placement that protects them from the hot sun.


Bonsai are ‘styled’ to give them a mature look and to give the illusion of a tree that has been shaped by the forces of nature. Wiring the trunk and branches is the usual technique employed, but there are other methods, such as using weights and clamps. Wires to pull branches downward are also used. The Chinese and Japanese have created many styles and bonsai source books give the enthusiast many different ideas to try. Click here for more on styling.

Water and Fertilizing

Of all the tasks to master in the cultivation of bonsai, watering is the most challenging. There are as many ideas about how to water as there are trees. One recommendation is to set the bonsai in a tub of water and let i soak, removing all the air bubbles. Another is the three-times method: water all the plants once, then again, and then a third time. A general rule of thumb is to give enough water so that it runs out the drainage holes of the pot in a steady stream. Do not let the water stand in a pot’s tray and do not water so little that there is no drainage. The best time of the day is in the morning or evening. Some bonsai like to have a more moist soil, other prefer a drier soil. It is good to ge in the habit of checking the trees every day. Feel the soil with a finger and judge if the tree needs water. Look at the leaves. Wilted, soft leaves mean too much water; browning, dry wilted leaves mean more water is need. Listen to the trees-they will tell you what they need!

This is another aspect of bonsai maintenance that must be approached as a science. There are two categories of fertilizer: Chemical and Organic. Chemical fertilizers can come in powder, pellets, or liquid form. Powdered forms must be mixed with water to be used. The greatest concern in using chemical fertilizers is that most directions for use result in too strong a solution that can burn the roots of bonsai It is recommended to use a weaker solution than is called for. Organic fertilizers reduce the worry of root burning. One drawback to organics is that some have an unpleasant smell and may not be desirable for use on indoor bonsai. Some organics are large pellets that are placed on the outside of the pot and take away from the aesthetic view of the bonsai. Even so, organic fertilizers are more eco-friendly for the bonsai and the environment as a whole. Fertilizing is generally done during the tree’s growing season, usually applied as often as every week to every two weeks for outdoor deciduous trees and conifers, and can be weakly applied year round every two weeks to indoor bonsai. Outdoor trees are usually not fertilized during the dormant period or at very least once a month. Some bonsaiists fertilize every time they water with a very weak solution. The watering is done fist then the fertilizer is applied. Always remember: Never fertilize a tree that is weak. This does more harm than good.

Pruning and Wiring

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Pruning is done to reduce the size of branches and leaves, and the roots are pruned to encourage more root growth to strengthen the tree. Roots are usually pruned by one-third to one-half their original length. Special pruning shears and clippers are used that come in various sizes. Prune above leaf nodes to chart the direction the next branch should take. Pruning is usually done on deciduous trees in the fall after leaf drop or early spring before the buds break. Spring is a good time for most evergreens, when new candles appear on conifers, or new growth appears on leafy varieties.

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Anodized aluminum wire is the most common choice when it is time to shape the bonsai. Care must be taken when wrapping the wire around the trunk and branches. Wrap the wire at a forty-five degree angle and watch out for leaves and nodes. Start with the trunk then wrap the largest branches, and finally the secondary twigs. Bend the trunk and branches gently to avoid breakage. For outdoor bonsai, wire should generally be left on the tree from six months to two years depending on the species and growth rate of the tree. Wiring is usually done during the growing season. The tree should be checked to make sure that the wire is not cutting into the bark. Ugly scars will be the result. Indoor bonsai can be wired at any time, but summer is preferred.


Bonsai is achieved by the confinement of the tree in a pot. The size of the tree will depend on the size of the pot. Mame bonsai are so small that the pot can have the diameter of a quarter! Reporting not only provides the tree with the chance to stay small, but also to grow larger. If it is desired that the tree grow larger, a pot’s length that is two-thirds the height of the tree is recommended. The primary reason that one repots is not only to give the tree a new home, but also new soil. Watering leaches out the minerals and nutrients that the soil provides. There are many bonsai soil mixes on the market but many bonsaiists like to make their own. Repotting also provides the opportunity to prune the roots but this does not have to be done every time one repots, especially if the tree is moving into a larger training pot. Repotting is usually done every year on young trees and every two to three years on older trees. Illustrated below is the process of repotting.

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Monthly Care

Eugene, Oregon is located in the Southern Willamette Valley between the Coastal Range and the Cascade Mountains. The average rainfall for Eugene is forty-four inches annually, and most of this rain falls from October to June. The summer months, from mid-June to mid-September receive little to no rain. Temperatures range from low 30’s in December to mid 90’s in July. The Monthly Care Guide is presented on four pages, in quarterly fashion. Some of the advice is provided by author Herb Gustafson.