Repotting and Wiring

Repotting

An uprooted bonsai, ready for repottingBonsai are generally repotted and root-pruned every two years around springtime, just before they break dormancy. Bonsai are often repotted while in development, and less often as they become more mature. This prevents them from becoming pot-bound and encourages the growth of new feeder roots, allowing the tree to absorb moisture more efficiently.
Pre-bonsai material are often placed in "growing boxes" which are made from scraps of fenceboard or wood slats. These large boxes allow the roots to grow more freely and increase the vigor of the tree. The second stage after using a grow box is to plant the tree in a "training box;" this is often smaller and helps to create a smaller dense root mass which can be more easily moved into a final presentation pot.

Wiring
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Bonsai wiring is one of the most powerful tools to control the shape of the tree.[4] The best time to wire a tree is in spring or fall when there is not as much foliage and the tree will not be too stiff. (Trees become stiff in winter while dormant because the sap pressure of the trunk and branches is much lower.)
One method of wiring the tree is to wrap the trunk. Then each branch is wrapped in spirals of bonsai wire so that the branch may be bent. The tree will then train the branch to grow in the desired direction. Another method of wiring involves attaching weights to the branches, causing them to sag and creating the impression of age.
Generally, wire is left on for one growing season. The tree should not be allowed to outgrow the wire, since this could cause the bark to become bound to the wire, making removal traumatic. When the time comes to remove the wire, it should be cut away in small pieces (rather than unwinding it), as this will cause less damage to the foliage.
The thickness of the wire used should be in proportion to the size of the branch — larger branches will require lower-gauge wire. Two pieces of thinner wire paired together can be used in lieu of heavier wire. It is bad form to let any wires cross; this is most readily accomplished by starting from the base of trunk and working up.
When bending the branches, one should listen and feel for any sign of splitting. When bending a branch near the trunk extra caution should be used, as the branch is generally most brittle near the trunk. It is possible to gradually bend a branch little by little over the course of several months.
When working with the branches, consideration should be given to the style desired.

Size Classifications, Techniques and Watering

Size Classifications
Additionally, bonsai are classed by size. Sizes of bonsai include:

Mame - tiny bonsai
Keshi-tsubu, up to 2.5cm
Shito, 2.5-7.5 cm tall.
Shohin - small bonsai
Gafu, 13cm-20cm
Komono, up to 18cm
Myabi, 15cm-25cm
Kifu - medium bonsai
Katade-mochi, up to 40cm
Chu/Chuhin - medium to large, 40-60 cm tall
Dai/Daiza - large bonsai
Omono, up to 120cm
Bonju, over 100cm tall
Note that sources disagree on the exact range of sizes given for a category.

There are a number of specific techniques and styles associated with mame and shito sizes, the smallest bonsai. These are often small enough to be grown in thimble-sized pots,[citation needed] and due to their minuscule size, require special care and adhere to different design conventions.

Techniques
Bonsai at the "Foire du Valais" (Martigny, Switzerland, oct 2005)Shaping and dwarfing are accomplished through a few basic but precise techniques. The small size of the tree and the dwarfing of foliage are maintained through a consistent regimen of pruning of both the leaves and the roots. Various methods must be employed, as each species of tree exhibits different budding behavior. Additionally, some pruning must be done seasonally, as most trees require a dormancy period and do not grow roots or leaves at that time; improper pruning can weaken or kill the tree.[3]

Most species suitable for bonsai can be shaped by wiring. Copper or aluminum wire is wrapped around branches and trunks, holding the branch in place until it eventually lignifies (converts into wood) and maintains the desired shape (at which point the wire should be removed). Some species do not lignify strongly, or are already too stiff/brittle to be shaped and are not conducive to wiring, in which case shaping must be accomplished primarily through pruning.[3]

To simulate age and maturity in a bonsai, deadwood features called "jin" and "shari" can be used to good effect with coniferous bonsai, especially. "Jin" are created by removing the bark from an entire branch to create a snag of deadwood, while "shari" involves stripping bark from areas of the trunk, simulating natural scarring by limbs being torn free. Care must be taken when employing these techniques, because these areas are prone to infection, and removal of too much bark will result in losing all growth above that area. Bark must never be removed in a complete ring around the trunk as it contains the phloem and will cut off all nutrient flow above that ring.

Watering
Because of limited space in the confines of a bonsai pot, bonsai care can be quite difficult. The shallow containers limit the expanse of the root system and makes proper watering somewhat difficult. Watering techniques vary, with some growers preferring to water with a fine rose on a watering can or hose, while others immerse their trees in a water-filled basin to the height of the container lip. [citation needed] While some species can handle periods of relative dryness, others require near-constant moisture. Watering too frequently, or allowing the soil to remain soggy, can promote fungal infections and "root rot". Sun, heat and wind exposure can quickly dry a bonsai tree to the point of drought, so the soil moisture should be monitored daily and water given copiously when needed. The soil should not be allowed to become dry, even for brief periods. The foliage of some plants cultivated for bonsai, including the common juniper, do not display signs of drying and damage until long after the damage is done, and may even appear green and healthy despite having an entirely dead root system.

History, Cultivation and Common styles

History

At first, the Japanese used miniaturized container-grown trees for decorating their homes and gardens.

During the Tokugawa period, landscape gardening attained new importance. Cultivation of plants such as azalea and maples became a pastime of the wealthy. Growing dwarf plants in containers was also popular, but by modern bonsai standards the container plants of this period were inappropriately large.[2] The then-term for dwarf potted trees was "a tree in a pot" (???, hachi-no-ki?).

Cultivation

Bonsai are not genetically dwarfed plants. They are created from nearly any tree or shrub species and remain small through pot confinement and crown and root pruning. Some specific species are more sought after for use as bonsai material. This is because they have characteristics that make them appropriate for the smaller design arrangements of bonsai. [citation needed] There are many different ways to acquire, cultivate and grow bonsai. Several of the most common include:

Growing from seed
Cuttings
Air layering
Grafting

Common styles

Bonsai Garden at the pagoda Yunyan Ta (Cloud Rock Pagoda; Suzhou, China)
Bonsai Trees showing a variety of different styles in Sydney, Australia.
A Pine bonsai in the informal upright style. This tree is more than 30 years old, in the Hidden Lake Gardens CollectionMany different styles of bonsai exist. In English, the most common styles include: formal upright, slant, informal upright, cascade, semi-cascade, raft, literati, and group/forest.

The formal upright style, or Chokkan, is characterized by a straight, upright, tapering trunk. The trunk and branches of the informal upright style, or Moyogi, may incorporate pronounced bends and curves, but the apex of the informal upright is always located directly over where the trunk begins at the soil line.
Slant-style, or Shakan, bonsai possess straight trunks like those of bonsai grown in the formal upright style. However, the slant style trunk emerges from the soil at an angle, and the apex of the bonsai will be located to the left or right of the root base.
Cascade-style, or Kengai, bonsai are modeled after trees which grow over water or on the sides of mountains. The apex, or tip of the tree in the Semi-cascade-style, or Han Kengai, bonsai extend just at or beneath the lip of the bonsai pot; the apex of a (full) cascade style falls below the base of the pot.
Raft-style, or Netsunari, bonsai mimic a natural phenomenon that occurs when a tree topples onto its side (typically due to erosion or another natural force) and branches along the exposed side of the trunk, growing as if they are a group of new trunks. Sometimes, roots will develop from buried portions of the trunk. Raft-style bonsai can have sinuous, straight-line, or slanting trunks, all giving the illusion that they are a group of separate trees -- while actually being the branches of a tree planted on its side.
The literati style is characterized by a generally bare trunk line, with branches reduced to a minimum, and typically placed higher up on a long, often contorted trunk. This style derives its name from the Chinese literati, who were often artists, and some of whom painted Chinese brush paintings, like those found in the ancient text, The Mustard Seed Garden Manual of Painting, depicting pine trees that grew in harsh climates, struggling to reach sunlight. In Japan, the literati style is known as bunjin-gi (???, bunjin-gi?). (Bunjin is a translation of the Chinese phrase wenren meaning "scholars practiced in the arts" and gi is a derivative of the Japanese word, ki, for "tree").
The group or forest style, or Yose Ue, comprises a planting of more than one tree (typically an odd number if there are three or more trees, and essentially never 4 because of its significance in Japan) in a bonsai pot. The trees are usually the same species, with a variety of heights employed to add visual interest and to reflect the age differences encountered in mature forests.

The root-over-rock style, or Sekijoju, is a style in which the roots of a tree (typically a fig tree) are wrapped around a rock. The rock is at the base of the trunk, with the roots exposed to varying degrees.
The broom style, or Hokidachi is employed for trees with extensive, fine branching, often with species like elms. The trunk is straight and upright. It branches out in all directions about 1/3 of the way up the entire height of the tree. The branches and leaves form a ball-shaped crown which can also be very beautiful during the winter months.
The multi-trunk style, or Ikadabuki has all the trunks growing out of one root system, and it actually is one single tree. All the trunks form one crown of leaves, in which the thickest and most developed trunk forms the top.
The growing-in-a-rock, or Ishizuke style means the roots of the tree are growing in the cracks and holes of the rock. There is not much room for the roots to develop and take up nutrients. These trees are designed to visually represent that the tree has to struggle to survive.