Bonsai is a work of art, a creative process which has evolved over centuries and which focuses on the natural beauty of the plant.
However, as opposed to other forms of art, this can never be considered as complete. The tree is a living organism which is continually growing and must be periodically shaped. To obtain the best results constant care is necessary, together with knowledge of styles and techniques of cultivation, an artistic sense, harmony and understanding between grower and plant.
The start of this journey should always be with what you cannot see, the roots of bonsai can spread! to fill its container completely in a few years, so it is important to transplant the tree before they start to grow out of the drainage holes or when they begin to emerge above the surface of the soil.
Before repotting, prune off about a third in volume of the root system and shorten the long, thick roots to promote the growth of feeder roots. All large cuts should be sealed with a waterproof wound sealant. Carefully remove as much of the old soil as possible from the container and replaced with a well draining mixture.
The frequency of transplanting depends on the training plan of the bonsai but in general young trees should be repotted more often than older trees. Fast growing species that produce abundant roots, such as boxwood or elms, may be transplanted in alternate years, whereas less vigorous old pines may be transplanted every three to five years.
The best time to transplant a tree is when the leaf buds (not the flower buds) are swelling and about to open. Flowering Bonsai like azaleas, wisterias and forsythias should be transplanted after flowering. Remove all decaying blooms at the same time. Fruit bearing bonsai such as quinces, apples and apricots should be transplanted in autumn, while conifers should be transplanted, for preference, in spring.