The frequency of Repotting depends largely on spesies, size and the age of each individuel tree; however, the technique is identical, regardless of any of these factors.

The best time to repot a tree is at the end of the dormant season, just before the buds begins to swell. Even through there is no dormant season as such, the growth slows down in winter and surges again as the days lengthen in spring. Spring flowering apples and cherries should be repotted in early fall, and azaleas and quince immediately after they have finished flowering.

Bonsai soil:

What is ideal for one may not be for the another. Fortunately trees are mostly rather adaptable and compromise readily. It follows from the foregoing that the soils used for bonsai culture should contain some sand, some organic matter, and some liquid retaining material. A good mix suitable for nearly all bonsai would be:

25 to 35% sand - particle size 1mm to 2mm;
65 to 75% coarse compost, which contains a small amount of silt

Some trees prefer acid soils with a ph below 7, whilst other thrive in alkaline conditions with a ph above 7. If it is known that a tree likes acid soil, peat may be added to the soil mix. Compost or leaf-mould should not be replaced by peat as peat is a sterile medium and contains no microorganisms infact it is not even supportive to microorganisms.     Other additions to soils may be substances such as bone, or hoof and horn meal, which is a slow acting phosphate. Care needs to be exercised when adding rich nitrogenous material such as animal manure or urea as they may burn the roots. Care should also be exercised when adding undecayed wood products such as bark or wood shavings as they use nitrogen in the process of breading down and may deplete the soil to the detriment of the bonsai.

The addition of charcoal may be helpful in the absorption of harmful gasses, and provide a sweet soil.

In order to accurately define the mineral content of soil the various sizes will be tabled as follows:

-Gravel 2mm or longer
-Sand 0.5mm to 2.0mm
-Silt 0.02mm to 0.5mm
-Clay 0.00mm to 0.02mm




If the particle in a soil mix is too fine, they clog and displace all air making it difficult for trees to survive. Some of the elements required by trees are taken up in the form of gasses through the roots or through the leaves. For most purposes, therefore clay is unsuitable.  The only exceptions is when a third layer of clay may be used to cover the roots of a newly planted rock clinging design tree, or where clay is used to confine the soil of a planting on a piece of slate or flat rock.  Due to the nature of clay it is difficult, when dry, to wet it, or once wet, it packs tightly, and spells a slow but definite deterioration to the tree.

Sand, as such, is usually a sterile medium, and water passes through at a very fast rate leaching out any nutrients it may contain. Some sand may contain elements, which dissolve slowly and alter, for example the pH.  Usually river sand is stable, whereas sea sand would contain salts, which could be harmful to trees.

Decaying organic material improves the friability and moisture retentiveness of the soil.  This organic material is a great source of nutrients for the microorganisms present in the soil and for the trees directly, both as macro and microelements.  In addition it provides such elements as vitamins and hormones, which are necessary to support life.

Loam is a mixture of silt, decaying vegetative and animal matter, trace elements and nutrients.  Loam is however an inaccurate description as it gives no clear indication of each constituent.  It also assists with moisture retention.

The removal of fine particles ensures good drainage (no clogging) and air capacity, and provides the roots with easy access.  The absence of coarse particles enables the soil to be worked in between the roots easily.

Make sure your bonsai soil provide stability for the tree, hold water and nutrients for the roots, and be sufficiently open to allow free passage of roots, water and air.  It must also be free draining.