It's like this- TREES WANT TO GROW! Just like animals want to eat, breathe... Trees want tog row new leaves, branches... ROOTS! Our job in caring for them on it's most basic level is to provide a soil medium that they can grow in. It is EASY as most will grow in almost anything!
Regular old Miracle grow potting soil? Hell YEAH! They will grow like weeds... But they will likely fill a small pot up with bpig old thick roots pretty fast and not develop a fine, ramified root system we desire for Bonsai...
"Pro mix" is very similar to Miracle a Grow- basically Peat, Pearlite, nutrients.. And most any potting soil of a similar constructions I'll give you similar results... Not bad for growing a tree out in a larger pot.. Inexpensive, makes happy trees!
Turface- more of a free draining component. Almost no ability to absorb and store nutrients, small particle size but- again trees WANT TO GROW- it produces solid results for most who use it, you can get a big ole 50 pound bag for like $15 if you find the right source... Not a great component to use by itself, but when mixed with some pumice and a little pine bark... Makes a great BONSAI mix. Napa oil dry a and the RIGHT KINDS OF KITTY LITTER ( composed of larger particles of diatomacious Earth, identical to Napa Oil dry...) are an ok substitute for Turface I suppose, but IMO are not as good. They don't hold up as well, have a lot of dust that turns to a muck when wet... You really need tow ash it out a bunch and let it dry before using...
Akadama- the holy grail! Boon's mix is basically a 1-1-1 combo of Akadama, pumice and lava rock. This produces a fast draining mix with very pourous material with lots of lagged edges- Akadama absorbs some nutrient and water, but not too much water, lava draines well but has lots of surpface area due to the jagged eves and this is where some water is retained... Makes a solid mix from what I can tell but only been usi it myself for about 2-3 months maybe so hard to tell much yet. Just can tell the mix looks good, drains GREAT, has enough weight not to float or wash out of the pot easily... Can't say anything but good stuff so far! According to most, this is the best mix, but is COSTS A LOT!
A Bag of Akadama apron half the sicze of the 50lb turface bag will run you around $40 or more... Pumice is comparable, maybe about $25-30, and lava rocks in size we want is just plain hard to find! If you can afford and can accumulate the Boon's mix ingredients, give them a try.
If you want something cheap that "works" but doesn't have the amount of air in the soil you can get from Akadama and larger grains like lava and Pumice... Give the turface/ Oil dry mixes a try... It is all about your needs, how many trees you have and how much you can or are willing to pay...
There are dozens of other ingredients people use- I have used chicken grit some as well. It is a good weighted ingredient but doesn't have the texture of lava and some people don't like the extra weight for larger trees... Mentioned pine bark- there is a very small grained type you can find at Lowes called "soil conditioner"- good stuff if you are using an organic component! Usually not well composted and you might have to pick so e chunks of wood out.. But it is good stuff!
Many many more options out there! Use what is available to you when you are repotting trees! Remember, unless you use something toxic, you probably won't kill the tree... Might affect the growth rate if you use a crappy mix though. A quote I love is: "you can grow a tree in marbles if youc are for it properly"- intended as a joke I guess then Anthony seems to be taking it too far! Lol. I don't reccommend 3 mm glass marbles.. Where doe you FIND THAT first off? Second though is the lack of texture/ porosity to the needs.. Limits drainage, air, has no BENEFIT for the soil the way an ingredient like Lumice or Lava rock would... He is basically cutting his "compost" with a grit that has not function except to take up space! Doesn't mean the trees won't like it- they LOVE growing in compost! Just seems a strange ingredient to me!
Good luck!
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