This post is intended as a heads-up to newbies, who are just getting started and are looking for a good soil for their trees.
I got my first bonsai trees earlier this year. My wife bought me a little ficus bush for my birthday (which I’ve recently air layered, post HERE), and I bought a small Japanese boxwood from Eastern Leaf. I also bought a bunch of Chinese Elm saplings from an online vendor.
When choosing a bonsai soil for the repots I performed on the ficus and boxwood, I only had a month or two of experience watching Mirai videos, and watching and reading other content online. At that point, the idea of growing a plant in “rocky” material like akadama, pumice, lava, etc, seemed a little wild to me. So when I saw an “Organic Blend Bonsai Soil Mix,” it seemed like a nice compromise. Some organic material (like what most people think of for soil), some “bonsai” soil. So I bought a bag and repotted my plants in it.
Six months later, and I can officially report that this soil is GARBAGE. When you water it, the soil compacts like cement. It literally never dries out. I keep my trees on an open window sill, with a small fan constantly blowing to create gentle air circulation. Even being next to an open window with a fan, this soil stays wet for over THREE WEEKS!
Going back to Eastern Leaf to read the description more carefully, I see it literally has sand as one of the components! The photo on their website looks nice and airy, with lots of pumice:
But in reality it looks like this:
Sorry the photo is a little out of focus. Honestly, the main components feel like sand and Turface. I know now that sand as a soil component was used very commonly, decades ago, and was even encouraged by bonsai greats such as John Naka. But in modern day practice sand is completely avoided because it is an extremely fine particle that compacts and eliminates air in the soil, hindering root growth and health.
I’ve also learned that Turface seems to be disliked by most bonsai practitioners today. The particles are small and flat, packing down like little bricks, and retain water for way too long.
This soil just compacts into a rock-solid mass. It has zero aeration, and never, ever, ever, dries out.
Eastern Leaf is a great company, but please stay away from this soil mix (unless, perhaps, you are in the hottest, driest desert environment and are only home to water your plants like once a week). To be fair to the company, they do say “ideal for good water retention and dryer climates.” But they also say it is their “best selling bonsai soil mix,” which would make one think it’s probably okay for most climates. It is not.
In conclusion, a word to beginners (which I still am, but far more educated six months later):
The single thing Ryan emphasizes above all else while discussing soil is maintaining a balance of water and oxygen. The main reason akadama (and pumice and lava) are used as bonsai potting media is they don’t compact (there are other important reasons, but this reason is fundamental). The particles maintain their integrity, which means tiny air spaces will always exist in and around the roots, alongside the water. Roots actually breathe. They need oxygen. Without it, they languish.
So please, avoid soils with components like sand and turface, which both compact and allow little-to-no air to exist around the roots, and which stay dry for weeks on end.
Also, please avoid the mistake I made of assuming organic components (such as peat moss and pine bark) are necessary. Bonsai trees do need a wide variety of nutrients, but supplemental nutrition is easily achieved with the use of organic fertilizers. Some organic material in your soil mix is fine, but the main body of the mix should be non-compacting components.