Guidelines For Creating Bonsai Soil
by Randy Clark, Charlotte, NC
The following are some general guidelines for the preparation of
bonsai soils. Unfortunately there are no hard and fast rules about what exact components should be included in a good potting mix,
but only about the particle
size of whatever components are selected by you. The
components of any mixture will vary from region to region and from garden to
garden. The exact composition will be dependant upon: 1. The types of materials which are available in
the area; 2. The local growing conditions
and, 3. The type of plant material.
Making Spaghetti Sauce!
The right composition for bonsai soil is like the right recipe for spaghetti
sauce. Everyone has a slightly different idea of what it should go into it. That's fine. Variety is the spice of life, but regardless
of what is included in a soil mix, it must always comply with two basic requirements. First and
most important,
the mixture should drain water quickly. Second, it should be
essentially pH neutral... that is, neither wildly acidic or basic.
A pH value somewhere in the 6.5 to 7.5 range seems best. There are all kinds of
pH testing kits available on the market. We suggest you get one and use it
to test your soils.
The objective for all the sifting and sorting of soil components discussed
below is that it produces a well draining, aerated soil mixture.
This is not rocket science. Don't get so caught up in selecting and
blending components for the world's most ideal bonsai soil that you forget the
main objective... drainage.
The logic of a good, well draining bonsai soil mixture should be
obvious if you just think about it for a moment. We are asking the tree to
grow roots in what is essentially an unnatural environment... the small confines
of a bonsai pot. When God created little green apple trees, he/she put them
in the ground and gave them root systems designed for that location. We
were the ones who came up with the idea of stuffing them into containers and
taking them to bonsai shows. The bonsai pot may suit our purpose and
vision, but it is an alien environment insofar as the trees roots are
concerned. Because the growing space in a pot is limited, we attempt to
gradually trim away heavier roots, thereby making more space for the
growth of fine feeder roots. It is the development of these fine feeder roots
that a good bonsai mixture is designed to promote.
It is a fact that the easiest
environment for development of fine rootage is a soil mixture which drains water
and aerates well. As proof, consider the mediums required for the rooting
of cuttings... sand or perlite. Both are substances which have a uniform
particle size and drain water well. Vigorous root growth in the limited space of
a bonsai container usually translates as vigorous top growth as well. Thus
a well draining and aerated soil mixture is an essential requirement for the
proper growth and development of your bonsai. Water must flow through the container easily and
not stand on the surface for any length of time. The things you put in
your soil mixture certainly are important, but regardless of the components,... if
the final mix does not have good drainage, it is wrong.
Der ain't no soil in bonsai soil!
The term "soil" is really somewhat of a misnomer. The
components normally used to create a good potting mixture are, in fact,
soilless. They are designed to
provide an ideal environment for root growth. In creating this
"perfect" environment we also create a few problems
for ourselves. First, it should be obvious to even a rank beginner that
the rocky concoction described below will dry out a
heck of a lock quicker than the sticky black potting soil which most people have been using
for years. Secondly, most of the components in the soil mix really are one
kind of "rock" or another, which means there is virtually no
nutrients in a properly prepared bonsai potting mix. Both of these aspects
are unfortunate, but necessary if our soil mixture is to have the success we
hope for.
Let's deal with the water issue first. Yes, bonsai soil will dry out a
lot faster than other soils. That does not mean you must quit
your day job and stay home to water the trees. There is no set formula for
how often a bonsai should be watered. Common sense should be the guide. The
primary objective is to keep the soil mass evenly moist, but not
soggy. Soggy soil results in root rot, which quickly results in dead
trees. Use the end of your finger. Insert it into the soil.
The answer should come automatically and naturally. Some people use
toothpicks or bamboo skewers inserted into the soil. It is interesting to
note that one of the advantages
of a properly prepared soil mixture is a soil mass which dries out uniformly,
... i.e., if it looks dry on the top, it's probably also dry on the bottom and
in the center.
With regard to the question of whether bonsai
should be watered on an hourly, daily, weekly, or monthly basis, the answer is...
Yes! For most beginner bonsaists the single most difficult thing
to learn is proper watering technique. By contrast, the secret to
proper watering technique is quite simple. Water the tree when it is
thirsty. If they would all dry out at the same time, we would not have a
problem. However, trees will dry out at different rates depending upon the
variety of plant; the time of the year (spring/winter/etc.);
the amount of roots in the pot: the depth of the pot; the
kind of pot (plastic or ceramic); the amount of wind and whether its
location is mostly sun or shade. A tree planted in the
ground and covered with grass or mulch would not dry out as quickly as the same
plant in a ceramic bonsai container sitting on a bench in the sun.
Considering the variables, there is no way to formulate a useful watering
schedule that suits everyone. It will change on a daily basis. Remember that common sense is the key.
You want the soil mass to stay pleasantly moist and not constantly rocking back
and forth between dead dry and sopping wet. You should apply water
accordingly.
Feed! Feed! Feed!
Secondly, the soil mixtures used in bonsai don't contain much in the way of
nutrients. If the tree is going to grow and be happy it must be kept on a regular fertilization schedule.
Take the time to learn a little about fertilizers and how they work with
plants. When you do you will discover there is no such thing as a special
bonsai fertilizer. Bonsai are plants and will eat the same things that
ferns and tomatoes do... nitrogen, phosphorus and potash. Whether
you choose a chemical or an organic fertilizer is your business. There are
advantages to both. (We will not discuss fertilizers in depth here, but
you should see our page on fertilizers). Just remember that a good potting
mixture does not retain fertilizer for very long and so it will be necessary to to
fertilize your trees at least every other week.
Bonsai Soil Composition.
A good bonsai mixture should be composed of about 75 per cent inert aggregate
and 25 per cent organic materials. What aggregate and what organic material is a
matter of some debate between bonsai people. Our suggestion is to use
materials that are available in your area to keep the costs and hassle to a
minimum.
Inorganically Speaking
Look around you and find the inert drainage
material (rock) locally. As you travel around the country you will
discover that soil components change by region based upon what is easily
available for that location. People in Florida use a
lot of sand in their soil mixtures. That's because they have got a lot of
it. Colorado bonsaists can obtain all the
decomposed granite they want from the sides of their mountains. In Hawaii
the primary inert component in a soil mixture is... you guessed it... crushed
lava rock. The inert ingredient(s) can vary greatly.... and that's OK. Here are a few
more:
Akadama - Akadama and Kanuma are particles
of pellitized clay which the Japanese use extensively for potting their
bonsai. Purists in the art of bonsai will tell you it is the only way to
go and that if you are not dropping $60 plus dollar per bag for this
product, you are not really doing right by your trees. Personally, I have
never been that impressed with akadama and kanuma... but I am certainly
impressed by Japanese trees, so perhaps I have more to learn. The bottom
line is that I have a lot of trees. If I were to start using akadama,
I would need a second mortgage on my house to afford it.
Turface - Looks a lot like akadama, but is
not. This product is used for the aeration of grass on golf courses
and baseball diamonds. It sometimes has chemicals added to it and is used
to soak up oil spills or for use as cat litter. Don't use either of these
products. Turface is usually only available in fifty pound bags, from turf
supply companies and generally not available at places like WalMart or
Home Depot. Essentially it is clay that has been heated in a fire until it
becomes hard and will not decompose (turn into mud) with prolonged exposure to
water. If you were to take a terra cotta pot and crush it up, you would have
essentially the same thing. Each particle is full of tiny holes which
absorb water and release it back to the plant slowly and its pH is relatively
neutral. Proper sifting of a 50 pound bag will net you about 25 pounds of
usable material for bonsai. Use the rest to aerate your garden.
Haydite - Haydite is the rock equivalent of
turface. It goes by a variety of different names (haydite, permatill,
staylite, etc.) and comes in different colors (brown or gray mostly) depending
upon what local you obtain it from. Historically, it is the primary ingredient
used in the manufacture of concrete blocks to make them lighter. Only in
recent years has its value as a soil amendment been discovered. Haydite is
actually expanded pieces of shale or slate. The term "expanded"
means it has been heated to over 2000 degrees which causes this already
porous rock to become even more porous. Like the turface it is full
of tiny holes which absorb water and release it back to the plant. Some
research even indicates haydite releases water more readily than does the
turface. Depending upon where it comes from, haydite can be slightly pH
acidic, which can be easily corrected by adding a little bone meal to your soil
mix.
Chicken Grit - We've used this substance for
years and swear by it. You can purchase it by the bag from your
local feed or farm supply store already separated into the correct grades.
Chicken grit is composed of fragments of crushed granite which farmers feed to
their chickens to help them grind up corn. (As it turns out, chickens have no
teeth). The particle size in any given bag will vary depending upon
whether it is intended for baby chicks or full grown turkeys. Unlike the
turface or haydite, crushed granite absorbs no water. It is, however, completely
inert, neutral in pH and has sharp edges on each particle which cause fine
feeder roots to split and divide when they hit them. A word of
caution. Make sure the chicken grit you are buying is granite. We
have found certain brands that are composed totally out of crushed sea shells,
which would be highly pH basic and disastrous in a bonsai mixture.
We have also seen chicken grit which is pink granite with white flecks. It
works fine mechanically, but is not aesthetically pleasing in a pot.
Construction Gravel - This is the substance most
often included in a good bonsai soil mix. It is basically river rock
and is the ingredient usually mixed with cement to make concrete.
You can find it "down by the riverside;" or at your local
construction site; or at the local concrete manufacturer; or in bags from places
like Home Depot or Lowes. If you purchase it by the bag make sure it is
all rock and not a rock/cement mix which would only compound drainage problems
the first time you watered. Seriously,... river rock, a.k.a. -
construction gravel, is an excellent addition to your soil mix. It's
inert, pH neutral and readily available in most areas. Don't
get it confused with the children's play sand and the blasting sand also
available at these home centers.
Organically Speaking
There are some bonsai growers who believe a good
bonsai soil mix need not contain any organic ingredients whatsoever. They
maintain that drainage and aeration are the two single most important aspects of
a good bonsai mix and that you, as the grower, have the responsibility for
putting in all the organic and chemical components your bonsai may
require.
This sounds a little too much like hydroponics to
us, although we are sure there is some merit to the argument.
The preference among most bonsai growers is to include something in
the finished soil mixture which, at least, looks a little like
"dirt." The organic component in an average soil mix is
usually about 25 percent of the total. This organic will decompose
gradually and release nutrient for the trees to use. In addition, it
will retains a bit more moisture than the inert components and will also absorb
fertilizer for the plant's use. The exact nature of the organic component
used is largely up to the grower. We use pine bark because it is
inexpensive and easily obtainable in fifty pound bags from our local garden
center. One bag yields about 25 pounds of usable material after it has
been passed through three sets of screens. Some people use oak leaf mulch,
some garden soil and some old compost, some decomposed sawdust. The list
can get quite long. Remember that the organic component is
simply a vehicle for dispersing nutrient and moisture and that it should be pH
neutral. You should also avoid using anything that might be too
"hot" (too much nutrient) for tender young roots, such as cow
manure or fresh compost.
Look Before You Leap
All components in a bonsai soil MUST be
screened. You will need a variety of screens ranging from half inch
through one/sixteenth. You can purchase ready made bonsai sieve sets from
your local bonsai supplier or visit the hardware cloth section of your local
building supply store. For a normal sized bonsai container (about 11" wide by 1 or 2 "
deep) the components described above should be screened to provide particles
which are about a quarter inch or less in diameter. Mixes for smaller bonsai (shohin
and mame class plants) should be screened to produce particles which are between
one eighth and one quarter inch.
A little common sense is the best approach when deciding what soil mixture is
right for you. The recipe above will produce a general soil mixture which is
good for all evergreens and most types of deciduous bonsai. However, sometimes
varying the mixture for particular types of plants can be a good idea. For
instance, plants such as azalea, which
prefer an acid soil would be benefit from the addition of an acidic
component such as peat moss. Likewise, if the plant prefers a damp
soil mixture (larches and bald cypress are a good example) more organics may be
called for. If the tree prefers a dry soil, (pine, ficus, juniper)
more inorganic may be advisable.
Take a look at the growing conditions in your back yard. If you have a shaded
location you may have problems with pots staying continually wet. In such a case
it might be wise to increase the aggregate content of your soil mix and thus
cause it to dry out more quickly. On the other hand, if your yard is
exceptionally sunny, you might want to add more organic ingredients which will
cause the soil to retain more moisture.
A Couple Of Tips
Moss - Decorative ground covers such a moss can add a great deal to a bonsai's
appearance. They can also be dangerous. Dry moss will actually shed water away
from the plant. If you use moss on your bonsai make sure that the moss does not
cover the entire surface of the pot and that you are always able to inspect the
condition of the soil. There is a Japanese rule which says moss may be
permitted to touch only three sides
of the container.
Removal of old soil - Try to insure that as much of the old soil
as possible is removed when transplanting. Incompatible soil mixtures can
cause problems in maintaining adequate moisture levels and fool you into
thinking the soil is completely saturated when it is not. If the old soil mass hold on to more moisture than the new
soil mix it may remain too wet and a condition of root rot will set in. This is
usually only a problem with plants collected from the wild. Trees that have been
grown in a proper bonsai soil mixture for a number of years normally
"release" most of their old soil particles upon transplant.
Soil Composition Protocol
Below is the soil mixture recommended by The Bonsai Learning Center. They
are what we have found to give good results over the years, but are by no means
the only mixture or combination possible. You
may wish to amend these ingredients to suit your own specific growing
conditions.
Standard Bonsai Mix
Components should be screened to produce particles of about 1/4 inch diameter
or less. Eliminate dust.
Haydite - 1 part
Granite or River Rock - 1 part
Turface - 1 part
Pine Bark - 1 parts
Shohin & Mame Bonsai Mix
Components should be screened to produce particles of 1/8 inch to 1/4 inch.
Eliminate dust.
Haydite - 2 parts
Turface - 1 part
Pine Bark - 1 part.
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This article has been reproduced with permission from Randy Clark of The Bonsai Learning Center.
You may visit his web site at "http://www.bonsailearningcenter.com/", or contact him at:
Randy T. Clark
Bonsai Learning Center
4416 Beatties Ford Road
Charlotte, NC 28216
Phone: 704-392-9244
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