When buying a tree from a store during the summer, be sure to give it at least 2 weeks outside, avoiding heavy rain and high winds before displaying it indoors. If purchasing in winter, however, do not allow it to be exposed to frost for the rest of the season, as it will probably have begun to shoot. This is most important with deciduous trees, and while varieties of junipers are very hardy it is as well not to take any chances.
Most bonsai are hardy trees and shrubs whose natural habitat is out in the open. They are not permanent houseplants; and even semi-tropical trees should be placed outside when weather permits. During the summer the plant must be able to carry out the process of photosynthesis, and during winter it is resting and building up its strength for the coming spring. Too long in a warm room will persuade it that spring has arrived early and it will start budding. If this happens more than once, the tree will simply die of exhaustion.
Sunlight, especially the ultra-violet ray, affects the growth of trees. Therefore, except in special cases such as immediately after repotting, extensive trimming, etc, bonsai should be placed in a sunny location. Bright light will also work well but the tree should not be placed more than 12" away from the direct light source. An east, west or southern exposure works best. A northern exposure will require the use of "grow lights" which should remain on up to 16 hours each day and the lamp should not be more than 2 inches from the top of the tree. Incandescent light is too hot and will not provide the various spectrum of light that is required to maintain your bonsai tree. If you do not have a window or light source that provides an east, west or southern exposure, be sure to select a bonsai tree that does well in lower lighting conditions.