Comparing common components

Shop for properties you can describe

Two growers recommend different ingredients, and both grow healthy trees. That does not make substrate choice arbitrary. It means more than one combination can provide the required functions, and the growers may have different pots, climates, budgets, and watering arrangements.

Begin with what you want a component to contribute: accessible water storage, persistent larger pores, weight, chemical behavior, or a locally repeatable supply. Then ask whether the particular product provides it. A familiar name is a useful introduction, not a specification.

Six illustrated sample dishes: pumice, dark lava, and brown akadama across the top; fired clay, bark pieces, and pale mineral grit below. — Illustrated component library. Appearance helps describe a sample; it cannot establish the grade, chemistry, or wet durability of a product.Illustration

Mineral components are not interchangeable

is porous volcanic rock. A graded horticultural product can offer internal water storage while helping preserve gaps between particles. It is often relatively light. Source differences matter: one batch may contain more dense particles, fines, or very large pieces than another. Ask what remains after preparation, not only how large the bag is.

, often sold as scoria, is another volcanic material, usually denser and relatively durable. Graded particles can contribute lasting structure and weight. Their pores and mineral composition vary, so “lava” does not mean zero water storage, chemically identical stone, or the same performance in every region.

is a Japanese granular clay-like material. It is valued for water-related properties and how roots develop through a granular medium. Grades and hardness differ. Some batches break down sooner under repeated wetting, root activity, or local weather. Budget for usable volume and future maintenance, not merely the purchase price. Its usefulness does not make it compulsory.

has been processed by heating. Other fired or expanded clay products differ in manufacture, hardness, pore structure, and size. A horticultural clay granule, an industrial absorbent, and a clumping pet product are not equivalents because all mention “clay.” Verify intended use, additives, particle grade, and wet stability before considering a substitute. Unknown additives or particles that turn to paste are reasons to reject a batch.

The Arnold Arboretum's published account of its bonsai collection describes a specific use of akadama and calcined clay. It is evidence of a collection's practice, not proof that the same ingredients or proportions suit every site. Arnoldia's account of the collection.

Organic materials have useful roles and limits

Horticultural bark is not the same product as fresh wood chips scraped from a woodworking bench. Aged or can contribute water retention, particle structure, and chemical exchange sites. Fine bark behaves differently from chunky bark. Processing and further decomposition change its behavior over time.

comes from coconut husks and can be sold as fine pith, fiber, or chips. Those forms are not physically interchangeable. Processing also matters: a horticultural product should have appropriate salt specifications. Peat and coir can hold substantial water, but adding a finely textured fraction to a coarse mix changes the spaces between particles as well as the ingredient list. UMass describes these distinctions in its discussion of media components. Effects of growing media on water and nutrient management.

Compare the tradeoffs, not a leaderboard

The tendencies below assume suitable horticultural material in a comparable particle grade. They are questions to verify for a batch, not laboratory ratings.

Component	Potential contribution	What to verify	Cost and sourcing question
Pumice	Internal water storage and an open granular structure	Grade, density, dust, consistent wetting	Is a regional supply available, and how much usable material remains?
Lava or scoria	Persistent particles and added weight	Pore structure, grade, mineral source	Does shipping heavy material erase a low bag price?
Akadama	Water retention in granular clay-like particles	Hardness, breakdown, consistency	Can you obtain the same grade again, and afford renewal when needed?
Processed clay	Potentially porous, repeatable granules	Manufacturing, additives, wet stability	Is the exact horticultural product reliably available?
Horticultural bark	Organic water storage and structure	Particle size, maturity, decomposition	Is there a consistent local by-product source?
Regional mineral grit	Weight and durable particle structure	Rock identity, size, dust, chemistry	Is it suitable and accessible without substituting an unknown material?

Exercise

The component comparison bench

Choose two samples, predict how to evaluate them, then wet and drain the illustrated trays. Switch to sourcing to examine the practical tradeoffs.

The substrate workbench

Compare function before reputation

A material can hold water inside its grains while leaving air between them.

Pumice

Lava / scoria

Akadama

Other clay products

Prepared pine bark

Regional alternatives

Compare these properties

Water, air & durabilityCost & sourcing

Sample A

Look inside the pale particles: internal pores matter as well as the gaps between grains.

Water: Water can enter connected internal pores.
Air space: Spaces between appropriately sized particles can reopen after drainage.
Durability: Usually durable; crushing and fines still vary by batch.

Sample B

Trade names and hardness grades describe products, not a single fixed pore system.

Water: Often useful water retention within and around the granules.
Air space: Intact screened granules create gaps; fines and breakdown can change them.
Durability: Grade, handling, roots, and conditions affect how quickly granules soften or break.

Observation 1 of 4

Inspect dry grains

Observation stageInspect dry grains

Reduced motion: Play advances one still observation. Back, Next, and the slider are always available.

Make a prediction

What would give the strongest basis for choosing between these samples?Compare the actual grade, wetting, and durabilityUse the better-known trade name as the deciding evidenceChoose whichever drains fastest, regardless of care

Water: solid blueAir / gas: dotted

Text description

Two trays show selected substrate components, with an enlarged example grain. Choose from pumice, lava, akadama, other clay products, prepared pine bark, and regional alternatives. Water is solid blue; intact particle surfaces and internal cavities remain visible after free drainage.

Advance through dry inspection, wetting, drainage, and comparison. Each sample has a complete observation and property card. A final question asks which evidence can support a component choice. No material receives an overall best score.

Illustrated example samples, not measured comparisons. Water retention, connected air space, and durability vary with particle grading, product, mixture, container, and conditions. Sourcing notes describe considerations, not live prices.

Choose two materials in the workbench. Explain one reason to include each and one uncertainty you would check. If you cannot name a function, the ingredient may be present only because a recipe said so. Likewise, excluding a material needs a contextual reason, not a slogan about “organic” or “inorganic.”

Price per usable batch

A cheap bag with a large discarded fraction may cost more per usable liter than a cleaner graded bag. Add transport, preparation, storage, and repeatability to the comparison. Do not assign a fixed global price ranking: pumice can be economical near a source and expensive where it must be imported.

Sourcing also includes extraction, processing, transport, and the use of regional by-products. Local does not automatically mean suitable or environmentally superior; imported does not automatically mean better. Favor a known, consistent supply that meets the required functions and avoids unnecessary waste. A small test is cheaper than discovering an unknown product changes character inside a valuable tree's pot.

The bonsai decision

Evaluate a replacement ingredient

Starting point

When a familiar material is unavailable, identify its job in the mix and compare a documented horticultural substitute in a small unplanted trial.

This assumes

You know the substitute's source, additives, grade, and intended use; you are preparing for future work rather than improvising during root exposure.

Change course if

Reject unsuitable additives or wet disintegration. Reassess proportions if retention, wetting, or usable volume differs from the original ingredient.

Practice check · not scored

A local fired-clay product costs less than imported akadama. What is the best next step?

Use the same volume immediately because both are clay.

Reject it because a bonsai must contain imported ingredients.

Check its specifications and wet durability, then compare a small batch in the intended container depth.

Optional · not required for completion

Write an ingredient specification

Choose one material and record its source, grade, processing, claimed properties, and unanswered questions. Do not collect material from protected land or assume unknown construction waste is horticulturally suitable. No-tree alternative: use the table and the workbench to write a three-question message you would ask a supplier; sending it or buying material is optional.

Back to the question

How can you compare ingredients without turning a trade name into a promise?

Compare the actual product by water storage, pore structure, durability, chemistry, consistency, and usable cost. Trade names help identify candidates; the batch and the growing situation determine whether they work.

Key takeaways

Pumice, lava, akadama, and processed clays have different possible roles.
Bark, peat, and coir must be described by form and processing, not only origin.
A material's grade and wet stability can matter as much as its name.
Compare cost after preparation, transport, and expected maintenance.