Wabi-Kusa Substrate & Material Ratio Calculator

Wabi-Kusa Substrate Calculator

Enter your ball diameter, the number of balls and a recipe, and the calculator returns the total mix to prepare, the volume of each component and the sphagnum wrap area. It works with the recipes in our substrate recipe guide and with the full build process in how to make a wabi-kusa. All ratios are by volume.

How to Use the Calculator

1. Measure the ball. Decide on a finished diameter. Beginners usually build 5-7 cm balls, which are easy to wrap and keep moist.
2. Enter the count. For a multi-ball display, enter the number of balls of the same size.
3. Pick a recipe. Use the baseline for most builds, the keto-free bentonite binder where keto soil is unavailable, the low-mold recipe for humid rooms and enclosed domes, and the traditional keto recipe if you can source keto soil.
4. Read the outputs. Total mix, per-component volumes and wrap area update together. Switch to imperial to see fluid ounces, cups, teaspoons and square inches.
5. Measure with one scoop. Convert the millilitre results to kitchen measures with the conversion table, then measure each pre-moistened component with the same set of measures.

The Squeeze Test: Hydration Check Before Shaping

The calculator gives volumes, but the final texture depends on hydration. After mixing, rest the substrate for 20-30 minutes and test it.

1. Take a handful of the mix and squeeze it firmly in your fist.
2. Open your hand. A good mix holds together as a clump that keeps the impression of your fingers.
3. Check for water. No more than a few drops should escape. A stream means the mix is too wet; add dry akadama or coir fines in small volume increments.
4. Poke the clump. It should crack into a few large pieces rather than crumble to dust. Crumbling means it is too dry: add dechlorinated or RO water a little at a time while kneading.
5. Repeat the test after any adjustment, then shape the ball.

A ball that passes the squeeze test stays aerated, which limits the oxygen starvation and surface wetness that drive mold. See the wabi-kusa mold prevention guide for the follow-up care.

Choosing the Right Recipe Preset

• Baseline Starter (60/30/10): the reliable default for beginners and for species such as Hydrocotyle tripartita, which roots readily in a nutrient-rich, moisture-retentive mix.
• Keto-Free Bentonite Binder (45/30/20/5): imitates the stickiness of keto soil using rinsed coir and a small dose of dry bentonite. Keep bentonite at 5-8% of total volume.
• Aerated Low-Mold (40/40/10/10): adds pumice or perlite for pore space. It is the best choice for sealed domes and humid climates, but it is less cohesive, so use a firm sphagnum wrap.
• Traditional Keto (50/30/20): the most cohesive hand-shaped result, but keto soil is hard to source outside Japan.

Handling Bentonite Swelling

Bentonite swells many times its dry volume when wetted. The calculator gives the dry powder volume, so measure it dry with a teaspoon, mix it into the dry or slightly damp akadama and aquasoil fines first, and only then add the hydrated coir and water. Let the mix rest 20-30 minutes so the clay hydrates fully before the squeeze test. Do not add extra bentonite after hydration to fix a loose ball, as late additions clump and seal pore space. Use only additive-free, unscented powder.

Scaling Multi-Ball Projects

Enter the ball count and the calculator multiplies the total, so you can mix one batch for the whole project. This keeps every ball identical and saves time. Mix in a tray no larger than your arm span can reach, and cover the bowl of unused mix with a damp cloth while you shape. Use batches the same day, since pre-moistened organic mixes start to sour after 24 hours. For plant palettes across several balls, see the wabi-kusa plants guide; taller stem plants such as Rotala rotundifolia work best on larger balls of 7 cm or more.

Limits of the Estimate

The calculator assumes a perfect sphere and a 15% allowance. If you flatten the base so the ball sits in a dish, build an oval shape or press the ball into a mold, the real volume will differ. If your mix is more tightly packed than usual, increase the allowance by weighing in a little extra. Leftover mix can be stored for up to 24 hours in a covered container in the refrigerator, and surplus dry components should be stored dry.