Potting Soils for a Bonsai

Important Soil Qualities

• The material you use to make a bonsai planting mix is crucial to the health of the plant. Traditional potting mixes or container soils are not suitable for growing bonsai. Any bonsai growing medium must provide ingredients that allow the trees to absorb water without remaining excessively wet, yet be loose enough to allow plant roots to breathe. Small bonsai dishes and pots inhibit overall growth because it is part of the process of keeping the trees small.

Homemade Planting Medium

• A good homemade bonsai planting mixture requires clay, clay gravel or grit, loam or sand, and humus, including peat or sphagnum moss, ground up leaf mulch or compost. You need a source of organic nutrition, something to help hold in the water, and something to provide proper drainage. The organic material breaks up the clay, gravel or sand to ensure air flows around the roots. You should be able to find all these ingredients at large home improvement stores, garden centers or plant nurseries.

Different Planting Mixtures

• A good all-purpose bonsai mixture should consist of equal parts of clay; humus or other organic matter, such as leaf mold or compost; and an inert substance, such as perlite, sand or crushed stone or granite grit. This all-purpose mixture is suitable for flowering trees or indoor bonsai.
  For evergreen trees, the planting medium should consist of 2 parts sand, 1 part peat moss and 1 part loam. Deciduous trees, or trees that lose their leaves, do best in a bonsai mixture that is made up of 1 part loam, 1 part peat moss and 1 part sand. Both conifers and deciduous trees can grow outside all year, and they naturally go dormant during the winter.

Repotting a Bonsai

• Bonsai need regular root pruning, and this is done when plants are repotted at regular intervals. To grow bonsai, you must prevent the plant from growing too quickly, and maintain the desired shape of the plant. The best time to repot a bonsai is in early spring before any new plant growth is visible.
  After removing the plant from the container, remove 1 inch of material, including roots and soil. You will be cutting into the root ball to remove both soil and roots. Use a sharp, sterile garden knife to remove 1 inch from the bottom and all around the sides.
  Remove any roots whose diameter is larger than that of a pencil. Radical root pruning encourages new root growth while preventing the large, killer girdling roots from growing. Repot the plant in the same container with fresh planting mix.