Basically, there are three main varieties of trees that are appropriate for cultivation as bonsai - namely coniferous trees, deciduous trees and ornamental shrubs. A brief discussion on each of these varieties is presented below.
Coniferous trees have been named so because of their cones or distinctive fruits. Nearly all conifers are evergreen trees and this helps them to maintain a steady form, notwithstanding the season. However, when we say that conifers are mostly evergreens, we do not mean that they never shed their "leaves", which are generally needles. However, these leaves or needles are continually and instantly substituted by new growths. This is the main reason why conifers always remain evergreen.
Conifers are excellent for growing as bonsai trees. They adapt themselves to bonsai treatment easily. Most importantly, pines readily accept the pruning of their branches. In addition, you can easily wire their branches and trunks to give them an arching form. Pines can also develop into stunning specimens in a very brief period - only a few years.
Usually, conifers are very resilient trees and, hence, they need minimum after care. This is one reason why conifers are excellent trees for a novice bonsai grower. In several instances, the only thing that growers need to do is just pinch out the shoots and buds in spring and remove the dead needles during autumn. Conifers have a performance for sunlit positions. However, you need to ensure that the root ball of the tree does not become dehydrated. It is worth mentioning here that since majority of conifers have their origin in the relatively arid regions of the world, you do not require watering them often or much.
Here is one thing that you should never forget. Scrape the bark of older conifer trees. This is important because such trees usually harbour various types of parasites. One parasite that is commonly found on the bark of most old conifers is the egg of over wintering greenfly.
Like the trees found in temperate forests, deciduous trees are also very familiar. These trees shed their leaves in autumn after an active growing season, which begins with the onset of spring or in mid-spring, subject to the species.
It has been proved that nearly all types of deciduous trees can be developed as bonsai. However, some are more suitable than the others. The most suitable deciduous trees include beeches, elms, horn beams and maples. These deciduous trees readily accept pruning of their leaves and shoots. In addition, most of these deciduous trees have their origin in the Far East and by nature they have an additional advantage - their leaves are very small. All deciduous trees change their color during autumn, creating a magnificent effect. Their color changes from different shades of green to anything ranging between gold and scarlet. This is considered to be an additional bonus of growing deciduous trees as bonsais and, to some extent, this compensates for their nakedness during the winter months.
When deciduous trees become habituated to the temperate climatic conditions, it becomes easier to grow them, depending on whether or not you are watering them properly and keeping the trees sheltered from the sun's heat. When a tree shows robust growth, it becomes necessary to keep its shoots within limits. This can be achieved by undertaking repeated pinching out of the buds and shoots to make sure that the tree has a bare minimum of leaves necessary for its survival as well as aesthetic beauty. Undertaking skilful pruning of the shoots during when the trees are in their dormant stage will help to give them your desired shape.
Precisely speaking, deciduous trees are ideal for use in a variety of group arrangements - they can be arranged in trays or even on any large stone slab. They are perfect for a quiet as well as graceful way of exhibiting bonsai trees.
All shrubs are ornamental trees, thanks to their beautiful leaves, blooms or fruits. Their decorative value makes them dear to many bonsai growers. Species belonging to the ornamental shrub group may be significantly different. This is because the only attribute that is necessary for them or that should be common to all the species is their decorative look. Therefore, we need to distinguish between shrubs that flower during spring, summer and winter; shrubs bearing fruits like those produced by any normal fruiting tree like the apple; and the shrubs that produce vividly hued, merely showy berries.
Even the growing techniques involved in developing these ornamental shrubs may be significantly different. This is also true for the pruning methods adopted to keep them in precise shape. Generally speaking, shrubs that flower early in the season - for instance, some shrubs produce flowers before the appearance of the leaves need to be pruned immediately when their flowers start wilting. On the other hand, shrubs blooming later in the season (either toward the end of spring or in summer) need to be pruned during the winter months. They can also be pruned prior to the commencement of new growths in spring. When a bonsai tree bears flowers and/ or fruits, it looks magnificent - mainly owing to the abundance of small flowers and fruits, as well as their diminutive size. However, the flowers and fruits of such trees are not as noticeable as their leaves.
Nearly all types of ornamental bonsai shrubs are of the outdoor variety. However, it is essential to protect the ornamental shrubs that have their origin in the Mediterranean region from frosts during the winter months.