BONSAI (2)

Cultivation

Bonsai can be created from nearly any perennial woody-stemmed tree or shrub species which produces true branches and remains small through pot confinement with crown and root pruning. Some species are popular as bonsai material because they have characteristics, such as small leaves or needles, that make them appropriate for the compact visual scope of bonsai. 

Sources of Bonsai Material

All bonsai start with a specimen of source material, a plant that the grower wishes to train into bonsai form. Bonsai practice is an unusual form of plant cultivation in that growth from seeds is rarely used to obtain source material. To display the characteristic aged appearance of a bonsai within a reasonable time, the source plant is often partially-grown or mature stock. A specimen may be selected specifically for bonsai aesthetic characteristics it already possesses, such as great natural age for a specimen collected in the wild, or a tapered, scar-free trunk from a nursery specimen. Alternatively, it may be selected for non-aesthetic reasons, such as known hardiness for the grower's local climate or low cost (in the case of collected materials). 

Propagation

While any form of plant propagation could generate bonsai material, a few techniques are favored because they can quickly produce a relatively mature trunk with well-placed branches.

Cuttings. In taking a cutting, part of a growing plant is cut off and placed in a growing medium to develop roots. If the part that is cut off is fairly thick, like a mature branch, it can be grown into an aged-looking bonsai more quickly than can a seed. Unfortunately, thinner and younger cuttings tend to strike roots more easily than thicker or more mature ones. In bonsai propagation, cuttings usually provide source material to be grown for some time before training.

Layering. Layering is a technique in which rooting is encouraged from part of a plant, usually a branch, while it is still attached to the parent plant. After rooting, the branch is removed from the parent and grown as an independent entity. For bonsai, both ground layering and air layering can create a potential bonsai, by transforming a mature branch into the trunk of a new tree. The point at which rooting is encouraged can be close to the location of side branches, so the resulting rooted tree can immediately have a thick trunk and low branches, characteristics that complement bonsai aesthetics. 

Commercial Bonsai Growers

Commercial bonsai growers may use any of the other means of obtaining starter bonsai material, from seed propagation to collecting expeditions, but they generally sell mature specimens that display bonsai aesthetic  qualities already. The grower trains the source specimens to a greater or lesser extent before sale, and the trees may be ready for display as soon as they are bought. Those who purchase commercially-grown bonsai face some challenges, however, particularly of buying from another country. If the purchaser's local climate does not closely match the climate in which the bonsai was created, the plant will have difficulties surviving and thriving. As well, importing living plant material from a foreign source is often closely controlled by customs regulations and may require a license or other special customs arrangement on the buyer's part. If a local commercial bonsai grower does not exist, buying from a distant one may be unsatisfactory. 

Nursery Stock

A  plant nursery is an agricultural operation where (non-bonsai) plants are propagated and grown to usable size. Nursery stock may be available directly from the nursery, or may be sold in a garden centre or similar resale establishment. Nursery stock is usually young but fully viable, and is often potted with sufficient soil to allow plants to survive a season or two before being transplanted into a more permanent location. Because the nursery tree is already pot-conditioned, it can be worked on as a bonsai immediately. The large number of plants that can be viewed in a single visit to a nursery or garden centre allows the buyer to identify plants with better-than-average bonsai characteristics. According to Peter Adams, a nursery visit "offers the opportunity to choose an instant trunk". One issue with nursery stock is that many specimens are shaped into popular  forms, such as the standard or half-standard forms, with several feet of clear trunk rising from the roots. Without branches low on the trunk, it is difficult for a source specimen to be trained as bonsai. 

Collecting

Collecting bonsai is the process of finding suitable bonsai material in its original wild situation, successfully moving it, and replanting it in a container for development as bonsai. Collecting may involve wild materials collected from naturally treed areas, or cultivated specimens found growing in yards and gardens. Mature landscape plants which are being discarded from a building site can provide excellent material for bonsai. In Great Britain, hedgerow trees that have grown for many years but have been continually trimmed down to hedge height provide heavy, gnarled trunks for bonsai growers.

Some regions have plant material that is known for its suitability in form. In North America, for example, the  California Juniper and Sierra Juniper found in the Sierra Mountains, the Penderosa  pine and Rocky Mountain Juniper found in the Rocky Mountains, and the  Bald Cypress found in the swamps of the Everglades. In Western Canada near the Rocky Mountains, wild larch are widely collectible and well-suited to bonsai cultivation.

The benefit of collecting bonsai specimens is that the collected materials can be mature, and will display the natural marks and forms of age, which makes them more suitable for bonsai development than the young plants obtained through nurseries. Some of the difficulties of collecting include getting permission to remove the specimens, and the challenges of keeping a mature tree alive while transplanting it to a bonsai pot.

Techniques

The practice of bonsai development incorporates a number of techniques either unique to bonsai or, if used in other forms of cultivation, applied in unusual ways that are particularly suitable to the bonsai domain. 

Leaf Trimming

This technique involves the selective removal of leaves (for most varieties of deciduous tree) or needles (for coniferous trees and some others) from a bonsai's trunk and branches. A common aesthetic technique in bonsai design is to expose the tree's branches below groups of leaves or needles (sometimes called "pads"). In many species, particularly coniferous ones, this means that leaves or needles projecting below their branches must be trimmed off. For some coniferous varieties, such as spruce, branches carry needles from the trunk to the tip and many of these needles may be trimmed to expose the branch shape and bark. Needle and bud trimming can also be used in coniferous trees to force back-budding or budding on old wood, which may not occur naturally in many conifers. Along with pruning, leaf trimming is the most common activity used for bonsai development and maintenance, and the one that occurs most frequently during the year.

Pruning

The small size of the tree and some dwarfing of foliage result from pruning the trunk, branches, and roots. Pruning is often the first step in transforming a collected plant specimen into a candidate for bonsai. The top part of the trunk may be removed to make the tree more compact. Major and minor branches that conflict with the designer's plan will be removed completely, and others may be shortened to fit within the planned design. Pruning later in the bonsai's life is generally less severe, and may be done for purposes like increasing branch ramification or encouraging growth in non-pruned branches. Although pruning is an important and common bonsai practice, it must be done with care, as improper pruning can weaken or kill trees. Careful pruning throughout the tree's life is necessary, however, to maintain a bonsai's basic design, which can otherwise disappear behind the uncontrolled natural growth of branches and leaves. 

Wiring

Wrapping copper or aluminiium wire around branches and trunks allows the bonsai designer to create the desired general form and make detailed branch and leaf placements. When wire is used on new branches or shoots, it holds the branches in place until they lignify (convert into wood), usually 6–9 months or one growing season for deciduous, but several years for pines (which maintain their branch flexibility through multiple growing seasons). Wires are also used to connect a branch to another object (e.g., another branch, the pot itself) so that tightening the wire applies force to the branch. Some species do not lignify strongly, and some specimens' branches are too stiff or brittle to be bent easily. These cases are not conducive to wiring, and shaping them is accomplished primarily through pruning. 

Clamping

For larger specimens, or species with stiffer wood, bonsai artists also use mechanical devices for shaping trunks and branches. The most common are screw-based clamps, which can straighten or bend a part of the bonsai using much greater force than wiring can supply. To prevent damage to the tree, the clamps are tightened a little at a time and make their changes over a period of months or years. 

Grafting

In this technique, new growing material (typically a bud, branch, or root) is introduced to a prepared area on the trunk or under the bark of the tree. There are two major purposes for grafting in bonsai. First, a number of favorite species do not thrive as bonsai on their natural root stock and their trunks are often grafted onto hardier root stock. Examples include Japanese red maple and Japanese black pine. Second, grafting allows the bonsai artist to add branches (and sometimes roots) where they are needed to improve or complete a bonsai design. There are many applicable grafting techniques, none unique to bonsai, including branch grafting, bud grafting, thread grafting, and others. 

Defoliation

Short-term dwarfing of foliage can be accomplished in certain deciduous bonsai by partial or total defoliation of the plant partway through the growing season. Not all species can survive this technique. In defoliating a healthy tree of a suitable species, most or all of the leaves are removed by clipping partway along each leaf's petiole (the thin stem that connects a leaf to its branch). Petioles later dry up and drop off or are manually removed once dry. The tree responds by producing a fresh crop of leaves. The new leaves are generally much smaller than those from the first crop, sometimes as small as half the length and width. If the bonsai is shown at this time, the smaller leaves contribute greatly to the bonsai esthetic of dwarfing. This change in leaf size is usually not permanent, and the leaves of the following spring will often be the normal size. Defoliation weakens the tree and should not be performed in two consecutive years. 

Deadwood

Bonsai growers use deadwood bonsai techniques called jin and shari to simulate age and maturity in a bonsai. Jin is the term used when the bark from an entire branch is removed to create the impression of a snag of deadwood. Shari denotes stripping bark from areas of the trunk to simulate natural scarring from a broken limb or lightning strike. In addition to stripping bark, this technique may also involve the use of tools to scar the deadwood or to raise its grain, and the application of chemicals (usually lime sulfur) to bleach and preserve the exposed deadwood.