The art of bonsai cultivation involves growing miniature trees in containers, intentionally styling them to resemble mature trees found in nature. This practice is a horticultural technique that relies on root pruning, branch pruning, and wiring to restrict growth. Not every tree species can withstand the rigorous training and container life required for this art form. Selecting a suitable tree depends on its inherent biological traits and natural environmental needs.
Essential Characteristics for Bonsai
A tree’s suitability for bonsai is determined by four primary biological characteristics that allow it to be successfully miniaturized and styled. The first is the plant’s ability to naturally produce small leaves or reduce leaf size through specialized pruning techniques like defoliation. If the leaves cannot be reduced proportionally, the miniature tree will not look realistic.
Another element is the internodal distance, the space between buds or points of growth along a stem. Species with naturally short internodes, or those encouraged to produce them through cultivation, result in denser, more compact foliage pads consistent with a mature canopy. Long internodes create a sparse appearance that is difficult to style.
The third characteristic is the tree’s tolerance for aggressive pruning, particularly the ability to “back-bud” on old wood. Back-budding occurs when dormant buds along the trunk or older branches sprout new growth after a hard cut, which is necessary to create a dense ramification of fine branches. Trees must also endure regular and substantial root pruning during repotting to maintain the tree’s small size and ensure a healthy, compact root system. Finally, a desirable species will develop bark that quickly becomes thick, fissured, and textured, giving the miniature tree the illusion of great age.
Hardy Species for Outdoor Bonsai
Hardy species are temperate trees that require a period of cold dormancy to complete their annual growth cycle, meaning they must be kept outdoors year-round. These trees are the traditional subjects of bonsai and are separated into conifers and deciduous varieties.
Conifers
The coniferous group includes species like the Japanese Black Pine (Pinus thunbergii), prized for its rugged, dark bark and ability to withstand harsh conditions. Pines have naturally long needles, but techniques like decandling can induce a second, shorter flush of growth, reducing the overall needle length. Spruces (Picea species), such as the Norway spruce, are also popular, known for their dense, short needles and conical shape. Unlike many deciduous species, conifers generally do not back-bud on old wood, making careful planning of their structure important.
Deciduous Trees
Deciduous trees are popular for their seasonal changes, offering displays of flowers, autumn color, and the fine branching structure revealed in winter. Maples (Acer species), particularly the Japanese Maple (Acer palmatum), are favored because their leaves reduce well in size and they offer brilliant fall foliage. Elms, such as the Chinese Elm (Ulmus parvifolia), are forgiving and tolerate aggressive pruning and a wide range of climates, making them a common choice for beginners. The European Beech (Fagus sylvatica) is sought after for its smooth gray bark and its ability to hold its small, dried brown leaves through the winter, a feature known as marcescence.
Tropical and Subtropical Indoor Options
For enthusiasts who live in climates with harsh winters or prefer to keep their trees indoors, tropical and subtropical species provide excellent alternatives because they do not require cold dormancy. These trees thrive in the consistent temperatures and lower light levels typical of an indoor environment.
Popular Indoor Species
A popular choice is the Ficus (Ficus species), which is robust, tolerates low humidity, and back-buds readily on old wood. The Hawaiian Umbrella Tree (Schefflera arboricola) is another forgiving indoor species, recognized for its glossy, compound palmate leaves that can be reduced in size with consistent pruning. This species is also notable for its ability to produce aerial roots in high-humidity environments, allowing it to be styled in the banyan-tree form.
The Fukien Tea Tree (Carmona microphylla) is admired for its tiny, dark green, glossy leaves and its tendency to produce small white flowers and berries year-round when kept in a warm, bright location. Dwarf Jade (Portulacaria afra) is a succulent that is resilient and forgiving of missed waterings, making it an ideal choice for a low-maintenance indoor bonsai. These tropical varieties are grown in temperatures above 60°F and must be protected from cold drafts or temperatures below 40°F.