Now there’s some pretty soil. 
With all the partisan political divisiveness of late, I figured that I’d introduce a calm, nuanced, and non-controversial subject into the æther. Try to, you know, relax the dialogues on the interwebs and facebooks a little, so to say. This is a safe subject. Indeed. It’s time to make the soil!
In that spirit, let’s talk about soil a little…..no one argues about soil, right? Before I begin, here are three links on soil from Da’ Blog: The epic one, The personal one, The update. Read them. There’ll be a test.
Let’s see now, we have lava (the pointy heads call it scoria. What do scientists know, right?) 
Lava is my go to, I’ve used nothing but it at times. It’s great for Florida, it doesn’t fall apart, has good shape and porosity, doesn’t hold too much water. Unfortunately, it doesn’t hold much nutrients either (this is called “cation exchange capacity” abbreviated henceforth as CEC. It is a measurement of the electrostatic charge of a particle in reference to fertilizer molecules. How much fertilizer sticks to a soil component. This is important in the coarse, granular soils we use because, startlingly, 75-80% of all fertilizer drains right out of the bottom of our pots. It helps for the soil particles to be able to hold a little between applications. At least I think so, there’s enough fertilizer pollution in Florida’s groundwater as it is now without me contributing to it too much more).
This next is expanded slate, a newer product that’s almost a ceramic, marketed by the Espoma company (and American Bonsai Tools too, I might add). It holds only about 10-15% of its weight in water and about zero CEC. I use it to improve drainage; in Florida we have rain, it being the Sunshine State and all. We can have more rain in a few hours than most places have in a month. This aggregate is basically to help keep my mix drier. 
Funny story, we once had a British gentleman (aren’t all British men, gentleman? Well, not really, I know one guy….likes to call other bonsai people names, not very “propah” at all, come to think of it….) visit the Orlando club and claimed that England had a lot of rain. Granted, it rains a lot in the United Kingdom of Great Britain, but it’s more like drool as opposed to the explosive projectile deluges we get here. Anyway, the funny thing is he kept asking if we had hawthorn yamadori and if we knew of a bloke called Tony Tickle. I said, “Mr. Tickle? Isn’t that a character in a children’s book? ” Hi Tony! Owe you a pint for that one.
Moving along, I have a pumice source now (the aforementioned American Bonsai Tools). I still don’t like the look of it but I’m liking most of the properties. Well, except for one: see, it doesn’t have a high CEC (because of the silica composition) but does, the way the pores work, (called index solution trapping) hold nitrogen in the surface matrix. What I’m learning and not liking is, when it’s relatively dry, it holds those nutrients and is very stingy in sharing with the plant, but in times of saturation, it will leach them excessively (as opposed to the way cation exchange happens). Here’s the scenario: in the summer, we have the flooding rains and then the heat dries the soil out pretty quickly. I’ll need to water again the next day if it doesn’t rain, ( I call this the “Wet/Heat/Dry Cycle”, it’s one reason why akadama doesn’t hold up well here). But, in the winter, the soil will stay wet for days, and pumice will give off too much fertilizer during these periods of saturation. Not good for trees that we don’t want to be actively fertilized at that time. I should add, this is mainly an American pumice problem (or what could be called a new pumice problem). The older the pumice or the more degraded it is, the higher the CEC will be. But that’s some high level stuff right there (go Here to read an abstract of a study done in Oregon on pumice, there are definitely some 25¢ words to learn) conversely, my favorite characteristic of pumice is it’s crushability by the roots. The roots need something to hold onto, to embrace and, much like the way your Aunt Joanne does when greeting you at the family Christmas get together, crush. Pumice should be soft enough for this (there are several grades of pumice. Everything from those stones you grind the callouses off your heels you get from wearing what my uncle used to call “come-hump-me-pumps, to horticultural grade. Which is really the cheapest grade. It’s soft, often floats, and works great in bonsai soil).
Since the pumice isn’t good at holding nutrients, my soil additive for that is pine bark, sifted, partially composted and ph controlled. I use Fafard organic soil conditioner. It holds water and fertilizer very well and the roots love it. And it’s a perfect medium for growing the microbes we need in a bonsai pot. I’ve written about mycorrhizal and bacterial symbiosis before, and every time I research it, there’s new information expanding our knowledge. The fauna down below is good for the flora up above.
I also use a calcined clay aggregate (OH NOOOOO!! The dreaded Turface!). It too has a relatively good CEC and holds water. It works good in Florida, much the way akadama performs but without the rapid breakdown that turns akadama into a brick. I don’t understand the vehemence that is shown towards this product. It’s not bad as a component in a soil mix. It could be this for one statement I overheard someone say “I’ve never deigned to even think of using a cheap product like that on my trees” that is the real antipathy. Take that as you will. In some parts of the country, turface is more expensive than akadama.
I will usually use an expanded shale product, but I’m out of it at the moment.
In case you haven’t figured it out yet (from this post and those linked above), I’ve done a lot of research and put a lot of thought into my soil. I don’t take someone’s word or use “traditional” soils just because they’ve been used for generations (For hundreds of years it was believed that bathing washed off the natural defenses that a body produced against disease. Before we discovered the germ theory of disease. And that bloodletting worked too, before we stopped believing in the “humours”. No one asked why though, did they?)
So here is this springs soil mix recipe. Notice that when I do my measurements, they’re a little heavy on some ingredients and lighter on others. Here you go:
One part lava (usually its two but I’m using pumice this time, an almost identical component)
One part pumice (and if you’re not pronouncing it “pooomice” you’re just not cool)
One part expanded slate (ignore the leaves and twigs, they don’t count)
One part bark (a little lighter on it).
One part calcined clay (and its “calcined” not “calcinated”)
This batch should get me through the next few weeks of repotting. Hopefully. A full batch fills an 18 gallon plastic bin. Like I said, isn’t that pretty? I should be a hand model.
Next few posts, I’ll be immersing myself in the wonderful world of the sugarberry tree.
Sweet.