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Where to buy Bonsai Soil Ingredients
Shelmerdine Garden Centre sells a pre-mixed, pre-sifted, 4 litre pail under the brand name Borealis. This is the classic 1/3, 1/3, 1/3 recipe described here.
The three individual ingredients are also available in small quantities at regular club meetings but you'll have to sift these ingredients before you can use them.
If you require larger amounts of bonsai soil, you can buy the ingredients in bulk which you can sift and mix as needed.
Crushed Quartzite is available in a 50 lb. bag from feed mills that supply Turkey grit to poultry farmers. Cherrystone Brand has the least amount of dust.
Turface is available in a 50 lb. bag from I.C.E Marketing on Keewatin Street. Ask for Turface MVP to get the correct particle size.
Bark chips are available from garden centres and come in a two cubic foot bag called Mini Bark Mulch. One bag of Mini Bark will yield less than 20% of its volume in the correct particle size. Be prepared for a lot of sifting.
1/3 crushed quartzite (turkey grit, no. 2 medium) provides ballast and helps to develop fine roots by providing hard, sharp points for the roots to grow around.
1/3 Turface, a fired clay that absorbs liquid water and slowly releases is as water vapour, a form preferred by the roots.
1/3 bark chips
Beginners must not be tempted to try using the rich, black loamy earth in which the trees in the yard are growing. For bonsai, loam results in a compacted growing medium which is difficult to water properly and thus can lead to tree mortality.
Before using any soil, you must sift out the very fine and the very coarse particles. Anything so fine that it falls through a sifting screen of 1/16 inch, (window screen size mesh), must be discarded as it will compact and prevent water from draining quickly. Any particles larger than 1/4 inch, that is, particles that will not pass through a 1/4 inch screen, must be discarded. Use whatever is left for your bonsai.
This 1/3, 1/3, 1/3 soil mix is a good general mix and most trees will thrive in it. Experienced bonsai artists sometimes adjust the mix to better suit individual trees with more specific requirements. Various bonsai books may recommend various other components or somewhat different proportions because their authors live in different climates or have different materials available to them. The above recipe works well in Manitoba!
At club meetings, beginners may hear members discussing extreme mixes, such as 80% shale in pines, or 100% Turface in figs. They may be getting favourable results, but beginners should not try these until well accomplished at keeping trees alive and healthy. The seasoned bonsai grower can detect and correct problems long before a beginner. These extreme mixes are unforgiving. Listen, learn, but wait.