Small trees grown in containers, like bonsai, require specialized care. Unlike houseplants and other subjects of container gardening, tree species in the wild, in general, grow roots up to several meters long and root structures encompassing several thousand liters of soil. In contrast, a typical bonsai container is under 25 centimeters in its largest dimension and 2 to 10 liters in volume. Branch and leaf (or needle) growth in trees is also large-scale in nature. Wild trees typically grow 5 meters or taller when mature, whereas the largest bonsai rarely exceed 1 meter and most specimens are significantly smaller. These size differences affect maturation, transpiration, nutrition, pest resistance, and many other aspects of tree biology. Maintaining the long-term health of a tree in a container requires some specialized care techniques:
- Watering must be regular and must relate to the bonsai species’ requirement for dry, moist, or wet soil.
- Repotting must occur at intervals dictated by the vigour and age of each tree.
- Tools have been developed for the specialized requirements of maintaining bonsai.
- Soil composition and fertilization must be specialized to the needs of each bonsai tree, although bonsai soil is almost always a loose, fast-draining mix of components.
- Location and overwintering are also species-dependent, and it is important to note that few of the traditional bonsai species can survive inside a typical house.