Bonsai is a horticultural art form that uses rigorous training techniques to cultivate a tree in a container. The word translates to “tree in a pot,” emphasizing the method of cultivation over the plant’s genetics. Bonsai size depends entirely on the artist’s intent and cultivation style, ranging from a few inches to several feet tall. This wide spectrum necessitates a formal classification system to standardize the art form.
The Traditional Size Classifications
The most widely accepted classification system uses traditional Japanese names based on the tree’s height, measured from the soil line to the top of the canopy. These categories provide a framework for understanding the scale, from miniature desk pieces to massive garden specimens.
- Shito or Keshi-Tsubu: Under 5 centimeters (2 inches). These “fingertip” bonsai require specialized care due to limited soil volume.
- Mame: 5 to 15 centimeters (2 to 6 inches). These are small enough to be lifted with one hand.
- Shohin: 15 to 25 centimeters (6 to 10 inches). This popular scale allows for high detail while remaining easily manageable for viewing and transport.
- Kifu or Komono: Up to 46 centimeters (18 inches). This is the largest size that can still be easily handled by a single person.
- Chuhin or Chumono: 41 to 91 centimeters (16 to 36 inches). Often called “two-handed” bonsai, they require two people to safely lift and move them due to their weight.
- Omono or Dai-Mono: 76 to 122 centimeters (30 to 48 inches). These are large garden display specimens.
- Hachi-Uye and Imperial: Exceed 152 centimeters (60 inches). These grand trees require significant effort and multiple people to relocate.
Factors Influencing Final Size
The final size of a bonsai is a controlled outcome achieved through specific horticultural techniques that induce a state of environmentally-induced dwarfism. The process begins with the initial selection of the tree, where species genetics play a foundational, yet limiting role. While virtually any woody-stemmed tree can become a bonsai, species with naturally small leaves, such as certain varieties of Japanese Maple or Juniper, are preferred because their foliage scales down more realistically to the miniature size.
The primary technique for restricting growth is regular and aggressive pruning of both the canopy and the root system. Canopy trimming is used to interrupt apical dominance, the natural process where the terminal bud suppresses lower and side growth. By removing the growing tips, the artist redirects energy to lateral buds, promoting denser, more compact branching.
Root pruning is performed during repotting, typically every one to five years, where up to two-thirds of the root mass is removed. This procedure is the most direct way to limit the tree’s size, as the reduced root system can only support a smaller amount of above-ground biomass. The stress from root reduction also affects the production of growth hormones like Gibberellins, further slowing overall growth. This restriction results in leaf miniaturization.
The limited volume of the container itself is the final, constant constraint on the tree’s growth. The shallow pot physically restricts the root ball, forcing the tree into a sustained state of limited resource availability. The selection of a fast-draining, mostly inorganic soil mix helps the artist control the precise amount of water and nutrients, allowing for careful management of the tree’s growth rate to maintain the desired size and proportion.
Size and Scale in Display
Beyond physical measurements, the size of a bonsai is defined by its aesthetic relationship to its container and its intended viewing environment. The concept of proportion dictates that the tree must appear visually balanced and natural within its pot. A general guideline suggests that the length of the pot should be approximately two-thirds the height of the tree, ensuring the container supports the visual weight of the canopy without overwhelming it.
The depth and shape of the container also contribute to the composition’s perceived size and stability. For instance, a shallow, oval pot is often paired with a delicate, feminine-style tree to enhance its elegance, while a deep, rectangular pot is used for masculine, rugged styles to convey strength. Taller pots are also necessary for cascade styles, where the tree’s growth extends below the base, to achieve a stable center of gravity.
The size classification determines where the tree is appropriately displayed. Smaller Shohin and Mame trees are ideally suited for indoor viewing on a desk or small shelf. Medium to large Chuhin and Omono trees are typically displayed outdoors on benches, or in a tokonoma, a traditional Japanese display alcove. The goal of the display is to create a harmonious scene where the tree, pot, and stand work together to evoke a sense of age and natural majesty at a carefully controlled scale.