Indoor bonsai are bonsai which are cultivated for the indoor environment. Traditionally, bonsai are temperate climate trees grown outdoors in containers.[1] Kept in the artificial environment of a home, these trees weaken and die. But a number of tropical and sub-tropical tree species will survive and grow indoors. Some of these are suited to bonsai aesthetics and can be shaped much as traditional outdoor bonsai are.
Note that bonsai and similar practices like penjing, hòn non bộ, and saikei all involve the long-term cultivation of small trees in containers. The term bonsai is generally used in English as an umbrella term for all miniature trees in containers or pots. In this article bonsai should be understood to include any container-grown tree that is raised indoors and regularly styled or shaped, not just one being maintained in the Japanese bonsai tradition.
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The largest difference between indoor and traditional bonsai is, of course, the enjoyment of an attractive, fully leaved plant in winter instead of a dormant, leafless tree. Other differences include the faster growth rate of tropical plants, which accelerate all steps of the bonsai evolution. Moss covering, a common soil covering for outdoor bonsai, will not survive indoor conditions.
Compared to the usual potted house plant, bonsai are rooted in a much smaller amount of soil. Consequently, they require more frequent watering and feeding.[2] This form is therefore best suited for drought-resistant species. Compared to usual house gardening, bonsais require a lot more pruning, both of branches and roots. This often requires a significant shift in attitude for house gardeners.
The spiritual benefits of bonsai cultivation, in Japanese bonsai no kokoro[3] are available equally to classical and indoor bonsai gardeners.
Many of the techniques used to grow and shape outdoor bonsai apply equally to indoor bonsai. For example, shaping techniques like pruning, wiring, and grafting work much the same for both types of bonsai. But indoor bonsai also have some special requirements for cultivation and care.
An indoor room comfortably lit for human use provides too little light for most species of tree to grow.[4] Few species will thrive with less than 500 lux available several hours per day. Successful indoor bonsai cultivation requires either selecting from the short list of low-light-tolerant trees, or providing additional lighting for the trees. Insufficient light may not kill some species outright, but will make their growth so slow that the bonsai shaping techniques cannot be used: the plant will not grow back after pruning or leaf trimming.
The simplest way to provide extra light is to place the bonsai close to an outside window. Care must be taken not to harm the plant either with cold air entering through the window, or with high radiated heat from direct exposure to the sun. More controllable light, and more flexibility in situating the bonsai, can be obtained using artificial lighting. Fluorescent lighting (preferably with bulbs radiating growth-friendly spectra) and light-emitting diode lighting can give sufficient light to support a significant number of indoor bonsai species. These lights also have the advantage of blending with other indoor lighting, so that the plants can be grown in normal living quarters. For plants needing the highest amount of light, or for large numbers of bonsai being maintained indoors, a space dedicated to bonsai cultivation can support high-intensity lamps and optionally the special ventilation or cooling often needed for their use.
Suitable temperatures for indoor bonsai extend from standard room temperature downward. The best temperature range for a tree is determined by its species and, less directly, by its normal range in the wild. Tropical trees are usually tolerant of room temperature year-round but cannot tolerate temperatures approaching freezing, as might occur near an open window in cold weather. Semi-tropical and Mediterranean-climate trees often grow better when temperatures drop well below room temperature during winter months. The lower temperature, combined with shorter periods of daylight, triggers an expected annual dormancy which many non-tropical species need in order to thrive. These non-tropical trees need a cool location in the winter, such as a cool window ledge or "cold room" area in the house. In addition to the need for seasonal temperature variation, many non-tropicals grow better when there is a distinct difference between day temperatures (warm) and night (cooler).
Indoor conditions, particularly in homes outside the tropics, imply very low humidity. Both air conditioning and room heating reduce air humidity significantly. Some tree species, such as ficus sp. with their waxy leaves, are tolerant of low humidity. Many species, however, require additional humidification to survive indoors. As with lighting, some humidification solutions can be integrated into the regular living area and some require a dedicated space. Local humidity can be raised by locating the bonsai containers over a tray of water, or by placing them in a bed of dampened sand. For better effect, the bonsai can be placed in enclosures, such as terrariums, that are humidified from within. For the maximum humidity, a dedicated room with high-capacity evaporative or misting humidifiers can support the most sensitive bonsai.
The creation of bonsai is limited only by the imagination and talent of the gardener, although some species are much more suitable than others. Members of the genus Ficus are among the most versatile, while many succulents can be grown in a similar fashion. Here is an incomplete list of the most popular species.
Small succulents may be used as accent plants:
With proper care, a number of non-tropical plants can also thrive as indoor bonsai.[8][9][10][11][12]