The art of bonsai involves growing aesthetically pleasing trees in containers that mirror their full-sized counterparts. There are no height requirements. Bonsai trees can be any size, from very small to quite large. Heights of the bonsai are dependent upon the bonsai's natural growth rate, as well as the growers' desires.
Trees that grow naturally upright and tall will do so as bonsais. The types of trees that you select for bonsai will greatly determine its growth characteristics. The Japanese maple, for instance, reaches natural heights up to 30 feet and will attempt to grow as vigorously for the bonsai grower.
Potting containers also help to determine the size of your bonsai. Trees such as Japanese maple tree require deeper, narrow pots to accommodate their height and downward growth of the root system. However, conifer bonsais, such as the Japanese black pine require wider, slimmer containers to accommodate the natural spread of the root system. Adjusting the depth or width of these containers helps to control height.
The pruning process helps to keep the bonsai healthy while allowing you control its height and shape. Hard pruning involves removing stems, branches and foliage from throughout the tree, as well as trimming back the central leader, if so desired. Hard pruning also includes root pruning which involves pruning down the root system so that the system is balanced with the bonsai tree.