- Roots need moisture and air to be healthy.
- Bonsai mix must drain well and supply constant level of moisture. Not too wet, not too dry.
- Soil mixes vary from grower to grower. Some people use a totally inorganic mix such as APL (Acadama, Pumice & Lava) and control the supply of nutrients with fertilizer similar to hydroponic growing. This type of soil needs to be watered 2-3 times a day without fail. I use a three part mix: One part organic material, one part drainage material, and one part moisture retention such as baked clay. This mix retains more moisture so it only needs to be watered once a day. Bonsai soil is sifted to remove fine particles that interfere with drainage.
- Placing different sizes of soil in layers as is recommended in some old books is now regarded as unnecessary. It creates a perched water table that interferes with capillary action and soil drainage.
- Types of organic soil components:
- Peat moss - Not recommended, acidifies soil, particles too small, breaks down too quickly.
- Ground bark/landscape mix - Best alternative, higher percent of useful sizes. Found at all nursery supply stores.
- Compost - If you make your own it's great but make sure it has reached sufficient temperature to kill diseases and weed seeds.
- Types of baked clay material:
- Expanded shale/Hadite - What concrete blocks are made from. Great material. Doesn't break down in soil. Found at gravel companies.
- Baked clay - Surface-Baked clay used for putting greens in golf and on running paths in baseball diamonds. Sometimes hard to find.
- Oil/Dry - I no longer recommend this product. It is no longer fired at a high enough temperature and breaks down quickly into fine clay.
- Water retentive stone:
- Kanuma - Soft pumice, traditional Japanese material. Very expensive.
- Agricultural pumice - Perlite that hasn't been fired yet. Heavier weight than perlite, not so prone to floating or blowing away.
- Drainage material:
- Lava sand - Sharp edges promote root branching. Contains iron that acidifies soil. Good material.
- Blasting sand/natural aquarium gravel - Already size sorted, so no sifting needed, very heavy, particles rounded so doesn't provide as much drainage as lava sand.
- Decomposed granite - Basically the same material as blasting sand, but contains a large variety of sizes. Much more waste.
- Starter chicken grit - Crushed granite. Hard to find now.
- Perlite - Pumice that has been quickly fired to pop it similar to how popcorn pops. White color is unattractive to some. Light weight. I use it more for plants under development. Easily found at plant nurseries.
- Root systems should be rejuvenated by periodically bare rooting a wedge of soil in the pot. Keep track of where you took the wedge out on a diagram in your potting notes, because you will have forgotten where it was when the next time to re-pot comes around. Next re-potting, bare root a wedge of soil from the side opposite where it was done before. After several re-pottings, the entire root ball will have been replaced with new soil and fresh roots.
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