Indoor vs. Outdoor Bonsai
There are many different species of plants that can be used for Bonsai, but not all have species require the same growing conditions. As a result there are Bonsai that must be grown outdoors, can be grown indoors, and should be grown indoors (depending on your geographic location and climate).
There are many varieties of plants that do well as indoor bonsai such as ficus, aralia, azalea, norfolk pine, serissa, gardenia, and boxwood. Note that these are all woody-stemmed plants and can have their limbs wired to direct the growth. Tropical and subtropical varieties can not tolerate temperatures below 40 - 50 degrees F; these plants can be left outside when the temperatures stay above this. Light inside the house should be by filtered sunlight from an east, south, or west window. Grow lights 12 hours per day work well. During the summer, these species can be placed outside in partial shade.
There is a wide choice of trees for outside bonsai. The winter dormant period is essential to the general good health of a bonsai. In northern climates winter protection from freeze-drying winds is necessary. Trees should be kept in an unheated area. An unheated garage, shed, breezeway, or cold frame can provide this. Check the root system for moisture and water as necessary while in winter storage. Unless the root ball is frozen they will need to be watered every week or so. In the summer water more often as weather conditions demand. Never let the tree go dry but do not keep it soaked either. Some of the trees suitable for outdoor bonsai are, junipers, maples, elms, pines, ginkgo, hawthorn, and flowering crab apple. For the most part, all evergreens are to be considered outdoor bonsai.