How to Make Bonsai Soil? | Mix Ratios That Work

A good bonsai soil uses a fast-draining, mostly inorganic mix of akadama, pumice, and lava rock, usually in equal parts, adjusted by species.

For the full breakdown, see our best Potting Soil For Bonsai guide.

Figuring out how to make bonsai soil comes down to one principle: roots need oxygen as much as they need water. Ordinary potting soil stays wet too long and collapses around the roots, which is why growers build their own substrate from coarse, porous particles. The goal is a mix that drains freely while still holding enough moisture for the tree’s needs, and that balance changes depending on what you’re growing.

The Common Mixes: What Goes In And Why

The three ingredients that show up in most bonsai mixes are akadama, pumice, and lava rock. Akadama is a fired clay that holds water and slowly breaks down over time; pumice provides aeration and moderate water retention; lava rock adds structure and fast drainage. The reference ratio used as a starting point is 1:1:1, then adjusted for the species.

The table below shows the ratios that appear repeatedly across reliable bonsai guides, including Bonsai Empire and Bonsai Tonight.

Deciduous trees like maples and elms prefer a wetter mix, so the higher akadama share works well. Pines and junipers want sharper drainage, which the equal-part mix delivers. Some growers in hot, dry climates lower the akadama and raise the pumice, since pumice releases moisture more slowly than akadama.

Making The Mix: Steps That Work

You don’t need fancy equipment to make bonsai soil at home, but you do need to prepare each ingredient before blending. The process is consistent across sources: sift, measure, mix, test.

1. Sift each ingredient. Pass akadama, pumice, and lava rock through a screen to remove dust and fine particles. Bonsai Empire notes that fines clog pore spaces and strangle roots.
2. Measure by volume in a clean bucket or container. Use a scoop or cup so the ratios stay consistent, and mix by hand until the particles are evenly distributed.
3. Test the drainage. Water the mix and watch how fast it flows through. If water pools on top, increase pumice or lava rock. If it runs through almost instantly and dries too fast, add more akadama or a small amount of organic material.

When the mix is right, water passes through the pot within a few seconds and the surface dries at a reasonable pace. One adjustment worth knowing: if you want more water retention, some sources suggest adding a small amount of potting soil, bark, or peat moss — but keep it to no more than 20% of the volume at first, and adjust based on how the mix drains.

Common Mistakes To Skip

The biggest error is using standard potting soil on its own. It’s too fine, holds too much water, and compacts easily, which leads to root rot. The second is skipping the sifting step, which lets dust fill the air gaps roots need. Another mistake is adding a gravel drainage layer at the bottom of the pot — a gardening guide from Gardening Know How explicitly warns against it, saying it can actually raise the water table inside the pot and keep roots wetter. If you live somewhere humid, lean toward a coarser mix; in warm, windy conditions, add slightly more water-retentive material.

For the pH side of things, bonsai soil should generally be near neutral. Mixes using akadama, pumice, and lava rock naturally land close to the ideal range, so pH adjustment is rarely needed for most home growers.

Once you’ve made your own mix a few times, you’ll build a feel for how your trees respond. If you’d rather start with a proven commercial blend instead of tracking down the three ingredients separately, our tested potting soil for bonsai picks list covers solid options for different budgets and experience levels.

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