Bonsai Soil – Part 2 – Major Soil Components

In the last blog posting we provided an introduction to bonsai soil and brief excerpts from Bonsai literature to give some history on the subject.  Here in Part 2 where we review the major components now widely used for bonsai potting soil.  In Part 3 in a future blog post, we will review some of the science, physics, chemistry and biology involved in potting soil composition and the culture of living trees in pots.

Watford Akadama – (from Bonsai Today Masters’ Series buy Latuda online canada Pines.)

Literally translated, akadama means red clay balls.  Akadama is the standard soil for most conifers, including pines.  It is excavated from quarries (between an upper layer of topsoil and a lower level of sand) in Akagi-yama in Honshu, 75 miles north of Tokyo.  The excavated akadama is not fired, but dried in hothouses.

Akadama has a pH of 6.5 to 6.9, slightly acidic to neutral.  Many enthusiasts use 100% akadama, particularly for pines and other conifers.  You can also use akadama as an ingredient in your current soil mix, as it works well in combination with other soil components.

Akadama drains extremely well, retaining only optimal amounts of water.  This encourages maximum root vitality and discourages root rot.

Akadama has a low cation exchange capacity, meaning it does not hold nutrients as well as some soils.  Because ongoing access to essential nutrients is so important, it is a good idea to use slow release fertilizers with akadama.

Akadama comes in soft, medium and hard granules, and in various sizes.  Generally, the larger the tree and pot, the larger the granules should be.  Because akadama is imported from Japan, cost can become an issue, especially if you have a large conifer collection.

A domestic mix

Turface or Haydite, bark, coarse sand and a small amount of mycorrhizal fungi medium is a fairly common mix used by American bonsai enthusiasts and professionals.  Some Bonsai mixtures utilizing Bonsai Grade Haydite are:

Deciduous: 55 – 65% organic material blended with 35 – 45% Bonsai Grade Haydite

Conifer: 25 – 35% organic material blended with 65 – 75% Bonsai Grade Haydite

Tropical: 65 – 75% organic material blended     with 25 – 35% Bonsai Grade Haydite

Haydite

Bonsai Grade Haydite is a specially sized and graded, highly durable ceramic-like material characterized by a microscopic, non-connecting, internal void system. The micro porous internal structure of the Haydite particles helps to maintain optimum moisture levels for vigorous, healthy plants.

Bonsai Grade consists of tiny sponge-like ceramic particles about ½ to 1/4th the size of a pencil eraser. Each of these tiny ceramic sponge-like particles possesses the unique ability to absorb excess water, and then slowly release the water back to the plant. Each particle becomes a tiny time-release capsule metering life sustaining water.

Those who practice the fine art of Bonsai have known for years that Haydite also offers excellent drainage and helps provide free passage of air and water to the root system which promotes vibrant, healthy plant growth while significantly reducing soil compaction.

Haydite is produced by expanding and vitrifying selected shale in a rotary kiln at temperatures in excess of 2000°F. This process makes Haydite sterile and environmentally inert. It is a natural, non-toxic, highly absorptive ceramic granule with a generally neutral pH. It is dimensionally stable and will not degrade or compress like other amending products.

Bonsai Grade Haydite should be mixed with the appropriate amount of organics and loam. Local climactic conditions will dictate what type of soil blend you should use for successful bonsai propagation.

Turface

Turface is widely available and reasonably priced.  It is a calcinated clay product.  If you get it for your bonsai mix be sure to get the variety MVP.

Turface is primarily used in athletic fields.  It is designed to shed water and, as to water retention, it is most like sand.  If Turface is used, I advise it not be used as the sole component in potting any plant.  But it does have value giving structure and drainage to a mixture if used in minor portions, (I would suggest never more than 33% of the mix).  Turface has no nutritional value.  Turface is dusty. I wash mine in water before use in a mix.  Although it is best if the potting mixture is dry when potting, damp Turface works as it doesn’t clump.

Sand

Many growers use or recommend sand in their mixtures.  Sand does help give structure and aids drainage.  Avoid fine sands, and especially ocean beach sands because of their salt content.  I get a coarse sand from a local landscape supply company.  After I wash and sift out the fines, I can use only about half the volume I bought.  I never exceed about 20% of the mix, usually less.

An excellent alternative, #12 grit, is used in construction.  It is not easy to find.  Its chief value is that it is sharp and rough and a little more coarse than the sands that are generally available.  Most available sand is smooth.  The coarse and sharp characteristic of grit holds moisture better, but still drains well.

Vermiculite

Vermiculite holds and releases moisture, and is valuable in giving texture.  Vermiculite, like all the other mineral components, brings no nutritional value to the mix.  Vermiculite is very light and does not give any mechanical weight to the soil mix, and thus does not contribute to the ‘foundation’ values of the soil mix for holding the tree upright in the pot.  Relatively small in size, vermiculite is a good mineral component for small shohin or mame bonsai.

Perlite

I have preferred perlite to vermiculite primarily because it is available in several larger particle sizes than vermiculite which is relatively small.  Otherwise its general characteristics are similar to vermiculite.

NOTE:  The dust from perlite, reportedly, is as dangerous as asbestos dust.  Whether true or not, I use great caution when handling perlite.  I wash it rather than sift, to clean out the dust particles so they don’t float about in the air.

Lava rock and pumice

Both lava and pumice are volcanic in origin and have similar properties.  They are porous, so hold some water in a soil mix.  They have no nutritional value.  They are fairly cheap, especially if you can find a bulk source.  Sometimes several people can get together and buy a half yard and split it.  That makes it pretty cheap.  Both come in several sizes.  A small, about 3/8”, particle size pumice is sold at the feed stores.  It is used as a bedding material for horse stalls and is called ‘Dry Stall’.  It is cheap and good, although quite dusty.  Again I wash mine rather than sift it.

Small lava rock is available from some Bonsai nurseries.  Lava rock comes in several usable sizes.  Small dark or black lava rock 1/8” or 3/16” is available and is sometimes used as a topping both for appearance and to protect the roots.

Pumice, like akadama, may be used as a specialty soil for sick trees or trees with root problems.  But great care must be taken that the tree and soil do not dry out and that adequate fertilization is maintained.  If used to plant a tree with poor or weak roots, in a short period strong vigorous roots may develop as in akadama.  Pumice requires greater attention to watering.  For this purpose akadama, in spite of its greater cost, may be a better choice.  

Other mineral components

Poultry grit is used by some. It is easily available and economic.  If you get poultry grit, be sure it is not crushed sea shells.

Cat litter

Cat litter is a calcinated clay product.  It is fairly small in size, but not fine.  If you get cat littler be sure it is unscented.

Crushed granite 

In the high Sierras you can almost always find piles of crushed granite off of little side roads where you can gather a few gallons.  It is good stuff, giving structure and weight to the potting mix.  Wash it, dry it in the sun, then sift it to get the sizes you’ll want for your mix.

Most landscape supply stores carry crushed granite, and it is not very expensive.  Crushed granite is heavy and may be best used with smaller or medium sized pots as it will make large trees heavier and more difficult to move.

A final note on mineral, i.e. non organic, soil components

They do not have or contribute significant nutritional elements to the soil mix, but they will release small amounts of their chemical makeup over time.  This is not adequate to meet the needs of living trees and is so marginal, it should be discounted when considering fertilizing requirements.  Mineral components give important structure to the potting soil, keeping it more porous than just organic material or fine soils.

Organic components

Many bonsai enthusiasts now use akadama as the sole component of their potting soils for pines and junipers.  I live in the Diablo Valley with very hot and dry summers and prefer some organic material in my mixes to help with moisture retention and soil temperature control.  The organics do not heat up, or (in our mild winters) get as cold as swiftly or as much as mineral components.  Tree roots are adapted to the more moderate ground temperatures and may be stressed by large temperature swings and the significantly higher and lower temperatures of the small bonsai pots.  Organic components in the soil mixture help to moderate both water loss and temperature swings.  But pure akadama mixes works well in the more moderate climates of the communities around the San Francisco Bay, and some enthusiasts in the inland valleys have good results using only akadama.

Many sources recommend either pine bark or fir bark.  Both are good organic components.  Availability and price may be the deciding factor.  Organic material breaks down over time in the pot environment, and that provides needed nutrients to the roots.  That break down also creates acidic by-products that increase the soil acidity (decreases the pH).  This is generally very moderate, depending on the local water characteristics.  East Bay Water is generally very slightly acidic.  Contra Costa Water District tends to be slightly alkaline.

Fir bark is more readily available in the San Francisco Bay Area than pine bark.  Some folks swear by one and swear at the other.  I know of no factual data to go one way or the other.

Other components now easily available include coco-chips and Oak Leaf Mold. Some composted materials are also available.  Be careful of Oak Leaf Mold or composted material as they may contain insect eggs or larvae.  If you use these, the old Japanese tactic of spreading it out in the sun for a week to ten days is a good option.  I bake my potting soil mixes for about 40 minutes either outdoors on the barbeque or in the oven at about 325 degrees to kill any obnoxious residents.  Solar is more economic and environmentally friendly.  Since we generally repot here in the winter months, if you choose to do the solar sterilization, you may need to start in October or November to have your soils ready for potting.

 

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