I’m often asked about the soil I use for my bonsai. Here’s a short blog about how I do it. There are countless formulas for bonsai soil, and the subject is one of the most hotly debated out there. My advice: find out what works for you. Here’s what works for me, and how I go about making it.

First things first. A bonsai soil must do a few things well. Here’s the short list:

  • Water retentive (the roots need water)
  • Aeratible (can help provide adequate air pockets; the roots must have air)
  • Free-draining (the water must not pool on the soil surface when you water – if it isn’t gone in one-Mississippi, you’ve got problems)
  • Not weigh a ton (there’s a limit to how light you can make your soil, and how light you should make it)

The photo at left is the larger-mesh of the two screens I use when making bonsai soil. Simple construction: a 1 x 4 x 8 cut into four equal lengths, assembled with deck screws. A piece of 1/4″ hardware cloth cut to fit and nailed to the underside with staples.

The smaller mesh screen. This one utilizes 1/16″ window screen. So that gives you an idea of the particle size soil I’m after. I use the larger-mesh screen to remove the chunks bigger than 1/4″, and the smaller one to remove the “debris” smaller than 1/16″ (which is sure to contribute to packing of the soil and water-logging plus anoxia for the roots).

If you make your own screens, the small-mesh screen needs to have a trim strip covering the window screen. If you don’t do this, it’ll rip away when you overload it with soil components.

Component 1: pine bark mulch. I buy it in bags from Home Depot. You can make a lot of bonsai soil with one bag of this stuff.

Here I’ve stacked the two screen, large mesh on top of small mesh. In goes a slug of pine bark mulch. It’s gotten wet from all the rain we’ve had lately, so I need to get it dried out.

Spread out on a nice warm day. It’ll dry pretty quickly. Then I lift the top screen and shake out some of the good stuff onto the bottom screen.

Here’s the good stuff, what stays on the small-mesh screen. I pick out any long but narrow pieces, spread it to dry, then shake it until I don’t see any significant small stuff coming through the bottom.

Component 2: Riverlite expanded clay lightweight aggregate. I use a 3/16″ coarse grade. I don’t know of anywhere you can buy this material in small quantities (I don’t sell it, so please no inquiries). You can use Turface(TM) as a substitute. I have used their All Sport(TM) product in the past. If you have a local landscape or sports park supply shop they should have it.

This is still wet from the rain, too, so I spread it out to let it dry.

Dried and ready to have the fines shaken out. This and the pine bark are mixed roughly 50:50.

The final product.

Water-elm #40 is starting to push buds now, so today was an ideal time to put it in a bonsai pot. Am I rushing things? Since I don’t have a lot of work to do in creating a tapering transition in the apex, the branch development work will go quickly even though the tree will now be in a bonsai pot. I know the tree is well-rooted, so the risk is low.

I’ve had this beautiful Chuck Iker pot for several years now. It was one of his first successful pieces sporting this particular glaze, which he calls “ancient jasper.” The color matches the new growth on a Water-elm very nicely.

The tree placed in the pot, and tied down.

And the soil all packed in tight. This tree should be in full leaf in about two weeks. Our weather had warmed up a few weeks ago, but then we had a cold snap that set many trees back a bit. Now it’s warmed up again, and I don’t think we have more than a few cool nights left this season.

I’ll post updates on this tree as it develops this year.

Let me know what you think of this composition. The pot may be a bit heavy for the specimen, but I’ll know better once I get some branch development.