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**When dealing with bonsai soil, we each have our pet mix. You would do well to talk with people in your area to determine what is working for them. Some soil mixes will not work in your area. This information is presented as is. It may not be relevant for your location and trees.
How’s Your Soil Mix?
by Jack Wikle, February 2001
"More has been said and written about soil with less understanding than any other bonsai subject," the words of Bruce Baker, well-known, Michigan, bonsai artist, who has a talent for cutting to the essence of a complex issue with a simple statement.
A bonsai-growing-doctor-friend, Greg Cloyd, tells me, "In medicine, when many different remedies are being used in treating a problem, you can be sure none of them works really well." Isn’t that the state of our bonsai soil struggle too?
I don’t consider myself a soil scientist, but I have been interested in soil mix issues and have read whatever I could get my hands on the subject for a long time. My Master's thesis almost 40 years ago was, "Selected Moisture Relationships and Irrigation of Container-grown Nursery Stock." But frankly, the more I learn, the more I realize how incomplete our soil mixing insights really are. Having said all that, I have an idea to offer here. The concept, in a nutshell, is that making some quick and simple porosity measurements can help us in refining our soil mixes. (See
instruction sheet which follows.) Basically, this approach is a modification of methods recommended by Dr. Carl Whitcomb, the container nurserymen's guru, in the 1998 revision of his book Plant Production in Containers and in his article in the Spring, 1991, Journal of the American Bonsai Society.
Admittedly, this focus on porosity and moisture retention is a bit narrow in that it ignores soil pH; it ignores cation exchange capacity; it ignores the "edaphon" (a word Greg Cloyd uses a lot that's not my dictionaries; meaning life in the soil) and it ignores a host of other factors in the soil equation. But, everything I've read, seen and heard supports the idea that space in our soil mixes is very important—space to let water in, space to let excess water escape and space to let air in after drainage. We may not agree on how to get there, but I'm guessing most successful bonsai growers will agree that a porous, open mix is our goal, and if we don't have that, we have a problem. The dirt gardeners' say it well,"moist but well drained," that's what we really want.
Back in the “dark ages” when I was in college, soil scientists were saying the ideal farm soil is 50% space; and, after draining, half of that space (25% of the soil volume) will be full of air and half (25% of the soil volume) will be full of water. Those numbers have been repeated again and again in soil and soil mix literature—even in bonsai soil articles. As recently as the Oct.-Dec., 1998, issue of Hort Technology, published by the American Society for Horticultural Science, Dr. Wm. R. Argo still cited these same percentages for field soil, in his review entitled "Root Medium Physical Properties."
Now how about container mixes? Are porosity and moisture retention targets for them the same as for field soil? Notes, for a talk I gave on soil for bonsai ten years ago, included this summary of my understanding at the time: "Good standards are not available, but your goal is as much water space as you can obtain without reducing air space too much. [The] evidence is that 10 to 20% of the total volume as air space [after drainage] is adequate for most of the plants we are interested in." My view today is that my thinking was exactly upside down. A better statement would have been, your goal is as much air-filled space as you can obtain without reducing water retention too much. In case you are thinking I was already behind on my reading, page 232 of Dr. Whitcomb's 1998 revision of his book, put it this way . . . air-filled space "values of 10% to 15% [percent by volume for fresh mix] are optimum . . . "
Less than two years ago, the big surprise, at least to me, came in measuring the porosity of Japanese akadama soil samples from Greg. Wow! This stuff really is different! It was like someone just lifted the bar I'd been trying to jump to twice its previous height. In my mind, this is the new standard: 60% plus total porosity, 30% air- filled space and 30% water-filled space after drainage in a 3.5" deep container. "More space than substance!"
It's interesting that since Greg and his akadama soil opened my eyes, I am now seeing other information supporting this new insight. Buried in the translation of a Japanese article ("Commonly Misunderstood Notions Concerning Watering." in Bonsai Magazine [BCI], Mar./Apr. 1994, page 43.), I found this statement: "A standard proportion recommended by professional bonsaiists consists of 40 percent solids, 30 percent liquid and 30 percent air." I'd never seen porosity numbers for Japanese soil mix ingredients before!
Then there was the statement by Ohio State University's Dr. Harry Hoitink in his June 1995 publication "Properties of Materials Available for Formulation of High Quality Container Media," "The air capacity of media used in nursery containers should exceed 20% for most crops and 25% for crops sensitive to Phytophthora root rots."
So, how do you know how porosity measurements for your personal mix compare with any of these “standards”? Let me assure you that you can't tell what you have by looking. You can't tell what you have by feeling the soil. You can't tell what you have by thinking about what's likely. You can tell by making some simple measurements.
One more bit of information captured in my notes. As Dr. Art Spoomer, who has written extensively on horticultural soil mixes, suggested at the 1980 American Bonsai Society Symposium at Michigan State University, it is very easy in mixing a variety of ingredients to come up with a mix inferior to any single ingredient used alone. Be wary of the "Witch's Brew” soil mix. Here's another case where less can be more.
Note: A percent by volume figure can be calculated by dividing a fluid ounce measurement, obtained following the instructions, by 8.5 and then multiplying the result by 100.
HOW'S YOUR SOIL MIX?
Quick and simple measuring of total porosity, water retention (after-drainage) and air- filled space (after-drainage)***
by Jack Wikle
Needs:
skeptical of any mix that does not accept
4 or more ounces of water (5 ounces and
even more is a better goal).
Air-filled space (after-drainage) is equal
to the amount of drainage water
collected. Drainage of less than 1.5
ounce or more than 2.5 ounces is reason
for concern too. Too little air-filled space
is a problem because it limits the
availability of oxygen to plant roots.
(Oxygen diffuses 10,000 times faster
through air than through water!)
Water retention (after-drainage) is equal to "water accepted" minus drainage. This is an indication of water available for plant use; but, unfortunately, this is not absolute because some of the water retained will be held so tightly on and within individual soil mix particles that it will not be available to plants.
- · Dry soil mix
- · Common 8.5 oz. "foam" coffee cup
- · Measuring cup calibrated in fluid ounces
- · Water to fill measuring cup
- · Tool (pocket knife?) for slashing drain holes in foam cup
Procedure:
- · Fill foam cup completely with dry soil mix.
- · Pour water slowly into soil mix adding as much water as possible; stop just short of overflowing.
- · Allow to set for 15 minutes and add more water if possible to bring back to almost overflowing level.
- · Record amount of water used then empty measuring cup.
- · While holding foam cup of saturated soil mix over the empty measuring cup, slash 3 or 4 openings in the bottom edge of the foam cup and catch the water that drains out in the measuring cup.
- · Record the amount of drainage water collected.
Interpreting results:
· Total porosity is equal to the volume of water accepted by the soil mix. Be very skeptical of any mix that does not accept 4 or more ounces of water (5 ounces and even more is a better goal).
·Air-filled space (after drainage) is equal to the amount of drainage water collected. Drainage of less than 1.5 ounces or more than 2.5 ounces is reason for concern too. too little air-filled space is a problem because it limits the availability of oxygen to plant roots. (oxygen diffuses 10,000 times faster through air than through water!)
·Water retention (after drainage) is equal to "water accepted" minus drainage. This is an indication of water available for plant use; but, unfortunately, this is not absolute because some of the water reqined will be held so tightly on and within individual soil mix particles that it will not be available to plants
*** Soil depth has a dramatic impact on the amount of water retained and air admitted after a thorough watering. To make valid comparisons between soil mixes, use containers equal in size and filled with soil mix to the same level.
BASIC SOIL MIX
BASIC SOIL MIX
by Brent Walston http://www.EvergreenGardenworks.com
QUESTION: I am interested in getting into bonsai. I see references to a "basic mix". Could someone tell me what goes into a basic soil mix?
RESPONSE: I am constantly experimenting with soil mixes and monitoring what others do. There is one generalization that keeps coming to the fore: A mix that is approximately half organic with no fines, such fir or pine bark, and half inorganic with no fines, such as lava, pumice, perlite, coarse sand, etc. I am convinced you can grow just about anything in a mix that has this as a base. You can add small amounts of other amendments to suit your climate and the species you grow. For example, you can add a small amount of peat for more water holding capacity or incorporate Osmocote“ to fertilize for the first season. I add a little native soil to inoculate the mix with hopefully good critters and for trace elements.
In general, I advise against using native soils or garden soil in amounts greater than about 5%. There are just too many fines and often clay that just turns container mix to muck. I have a lot of experience with mucky container soils and have vowed to only use materials that are long lasting, that is, they don't break down at all, or only slowly in the case of organic amendments. I am a firm believer in the merits of fresh fir bark. I smell it to make sure that all those good volatiles are still in there.
The drawback to such mixes is that they don't hold much in the way of nutrients, so you must monitor them very closely for fertilizer. You definitely cannot be lackadaisical about the feed. The result of neglect will soon be evident in the form of chlorosis.
I tinker and tinker with my soil mix, but the latest formula which has been giving me pretty good results for the last year is as follows. I use this to pot newly rooted cuttings and for bonsai as well. Remember that you can replace the organic and inorganic amendments with anything similar. There is nothing magical about any component. By the way, I don't use Superthrive“ or B1, or any thing of that kind of thing. It is much more important, in my opinion, to pay close attention to the principles of horticulture, rather than the hype of manufacturers.
Transplant Mix
- · 6 parts perlite
- · 4 parts fir bark
- · 1 part medium vermiculite
- · 1 part peat moss
- · Osmocote (medium rate of incorporation, see the label)
·
2 cups CLEAN soil (I use creek bed silt)
· 1/8 cup Gypsum per 2 cubic feet
· 1/8 cup Sulfur flour per 2 cubic feet
· 1/8 cup Ferrous sulfate per 2 cubic feet
The last three are rather whimsical, but I would recommend incorporation of some form of calcium and magnesium. If you live in hard water areas, use gypsum; if
in acid rain areas, use dolomite. Microorganisms love sulfur, and a little shot of iron never hurts.