Zeolite, perlite, biochar, or expanded clay – what does your garden really need?

You're standing in front of the shelf at the garden center or scrolling through an online shop and you see: zeolite, perlite, biochar, expanded clay. All of them somehow promise the same thing - better soil, healthier plants, more yield. But what's the actual difference? And what exactly do you need for your raised bed, your pot, your lawn?
That's exactly what we're going to clarify today. Without jargon - just an honest explanation.

First, why use soil additives at all?

Good soil isn't a given. Many garden soils are too sandy (water drains through, nutrients leach out), too clayey (compacts, waterlogging), or simply depleted after years of intensive use. And even in a pot with fresh potting soil, things can go wrong after a few months: the soil compacts, nutrients are washed away when watering, and roots get too little air.
Soil additives - i.e., additives like zeolite, perlite, biochar, or expanded clay - are designed to solve precisely these problems. Each has its own character, its own strengths. None is universally the best. And many work best in combination.
Let's get started.

1. Zeolite - the all-rounder with deep impact

Zeolite is a natural volcanic mineral that forms when volcanic ash reacts with alkaline groundwater. The result is a crystalline structure with countless tiny pores - a natural molecular sieve that can actively bind and release water, nutrients, and even pollutants.

What zeolite can do:

• Store water and release it buffered - not just hold it, but release it when needed
• Bind nutrients - nitrogen, potassium, magnesium, calcium remain in the root zone instead of being washed away by the next rain
• Promote soil life - the porous surface provides an ideal habitat for microorganisms
• Bind pollutants and ammonia - particularly valuable in compost and heavily fertilized soils
• Act long-term - zeolite is a mineral, it does not decompose. Once incorporated, it remains active for years

Which zeolite for which application?
Not all zeolite is the same — and that also applies to our two Steinkraft products:

BODENKRAFT ZEOLITH 0.5–1 mm is a natural zeolite granulate. The granulation makes it ideal for incorporation into garden soils, beds, raised beds, and lawns. It distributes evenly, is easy and clean to apply, and remains active in the soil permanently. The grain size is optimal for the root zone - not too coarse, not too fine.

BODENKRAFT ZEOLITH PULVER PUR is tribomechanically ground zeolite with a grain size of 100 µm - fine powder. The tribomechanical pulverization process keeps the internal crystal lattice structure intact (and this only applies to this process), which increases its effectiveness many times over. This product is particularly suitable as a foliar fertilizer, for soil activation in case of poor soil life, and wherever a particularly fine, rapid distribution is desired.

Where zeolite works best: Vegetable beds, raised beds, lawns, potted plants, when planting shrubs and trees, in compost. In short: almost everywhere.

Where caution is advised: For acid-loving plants such as blueberries, rhododendrons, or azaleas. Zeolite can slightly raise the pH value — these plants do not like that.

💡 Our tip: Zeolite unfolds its full effect in combination with active microorganisms. The AM+PLUS mother solution from Steinkraft revitalizes soil life and works hand in hand with the storage structure of the zeolite - minerals provide structure, microorganisms bring dynamism. This combination is significantly more effective than zeolite alone.

The difference to the other materials mentioned: Zeolite is the only one of the four materials that actively stores and releases nutrients (high cation exchange capacity!). The others primarily improve the physical soil structure - zeolite does that too, but much more besides.

2. Perlite - the aerator

Perlite is volcanic glass that is "popped" at extreme heat (over 1000°C) - similar to popcorn. The result: ultra-light, white spheres with an open pore structure.

What perlite can do:

• Improve aeration - perlite keeps the soil loose and ensures air reaches the roots
• Promote drainage - excess water drains faster, preventing waterlogging
• pH-neutral - does not chemically affect the soil
• Very light - ideal for pots and containers that need to be moved

What perlite cannot do: Store or release nutrients. Perlite is chemically inert - it purely improves the physical structure but has no active effect on nutrient supply.

Where perlite works best: In substrate mixtures for houseplants, cacti, succulents, orchids. Anywhere where drainage and aeration are paramount and the plant prefers drier conditions.

A small catch: Perlite breaks down on its own after about 5 years and disintegrates into dust. So it's not a permanent solution and needs to be replaced regularly. It also gets dusty when mixing - it's best to moisten it slightly beforehand.

3. Biochar - theoretically interesting, but with an important caveat

Biochar (also known as charcoal) is produced through pyrolysis - heating wood or other organic materials in the absence of oxygen. The result is highly porous carbon with a very large internal surface area: up to 500 m² per gram, compared to 30-60 m² for zeolite.
On paper, this sounds impressive. In practice, however, there is a caveat that we do not want to hide.

⚠️ The heavy metal problem - how it arises
Every plant naturally absorbs traces of heavy metals from the soil through its roots. This is normal. The problem arises during the pyrolysis process itself: during pyrolysis, the organic mass is reduced to a fraction, but the heavy metals remain completely and concentrate on much less total mass. What was previously harmlessly distributed is then crammed into a small space. While heavy metals in good biochar are bound and, according to current research, not directly plant-available, science cannot yet say with certainty how permanent this binding is.
It becomes particularly critical if the starting material is already contaminated: treated old wood, green waste from roadsides or industrial areas, or sewage sludge. In these cases, the contamination in the finished charcoal is significantly higher.
In addition, there is a second problem: improper pyrolysis can produce polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic compounds that can settle on the charcoal surface. Only industrially and correctly produced biochar from controlled facilities is free of these.

What biochar can do - if the quality is right:

• Very large internal surface area as a habitat for microorganisms
• Long-term carbon storage in the soil (Terra Preta principle)
• Build soil structurally over decades - it does not rot

What biochar cannot do: When used fresh from the bag, it has little effect - it is initially an empty reservoir that must first be loaded with nutrients. This takes weeks to months. Anyone who incorporates biochar in spring and expects a good harvest immediately will be disappointed. Too much or unloaded charcoal can even draw nutrients from the soil and inhibit growth.

Where biochar makes sense: Only where its origin is completely traceable, heavy metal-free and PAH-free status are proven - and as a long-term measure for soil building, not as an immediate solution.

Zeolite vs. Biochar - the direct comparison

This is a question we get asked a lot. And the answer depends on what you need - immediate effect or long-term soil building.

Start of effect: Zeolite works immediately. As soon as it is incorporated, it begins to store water and bind nutrients. You will see effects in the first season - less watering, more stable nutrient supply, healthier plants.
Biochar needs time. When freshly introduced, it is practically empty - an empty reservoir that must first be filled. This takes weeks to months, depending on how active the soil life is.

Application: Zeolite as granules (0.5-1 mm) can be easily and cleanly incorporated into the soil - no dust, no discoloration, no sticking. The powder (100 µm) is finer and can be easily washed in with water or integrated into substrate mixtures.
Biochar is deep black, very dusty, and stains everything - hands, clothes, tools, light patios. This is not an exclusion criterion, but it is much more cumbersome in practice.

Safety for food plants: Zeolite is a pure natural mineral of volcanic origin - without organic starting materials, without heavy metal risk from the manufacturing process. The safety of biochar depends heavily on the quality of the raw material and the pyrolysis process. For vegetables, herbs, and fruit plants, zeolite is the clearly safer choice.

Conclusion of the comparison: If you want to make an immediate impact, zeolite is the right choice. If you want to build soil for the next 20 years and the quality of the biochar is completely verifiable, it can be a useful addition - but only as an addition, not as a substitute.

4. Expanded clay - the classic for drainage and hydroponics

Expanded clay (also called LECA - Lightweight Expanded Clay Aggregate) is produced when low-lime clay is fired at over 1200°C. The small clay balls expand and get a porous structure.

What expanded clay can do:

• Drainage - as the bottom layer in the pot, it reliably prevents waterlogging
• Aeration - keeps cavities open, roots get air
• Water storage - stores some water and releases it slowly
• Structurally stable - does not decompose, can be reused for years
• Ideal for hydroponics - expanded clay is the classic substrate for soilless plants

What expanded clay is not good at: Storing and releasing nutrients - it does this significantly worse than zeolite. It is also comparatively heavy, which can be a problem with large pots.

Where expanded clay works best: Drainage layer in pots, hydroponics, heavy garden soils with waterlogging problems. Less suitable as a soil improver in beds - zeolite or perlite are more effective there.

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A look behind the scenes: What about energy and sustainability?

Anyone who gardens truly sustainably doesn't just think about what goes into the bed — but also what happened before to produce the product. And here, the four soil amendments differ considerably.

Expanded clay - the energy hog
The production of expanded clay is very energy-intensive: The clay is fired at over 1200°C. The primary energy demand is approx. 700 to 3500 MJ (megajoules) per cubic meter, depending on the density, and the greenhouse gas potential is around 96 kg CO₂ equivalent per cubic meter. In addition: The special clays for expanded clay are only available in limited quantities as exploitable deposits in Central Europe - raw material scarcity is emerging in the long term.

Perlite - energy plus long transport routes
For production, raw perlite rock is expanded to 20 times its original volume at about 1000°C. The energy demand is about 9 MJ (megajoules) per kilogram. Of this, transport costs account for up to half, as the raw material mainly comes from the Greek island of Milos and reaches Central Europe by sea. Perlite is therefore doubly burdened: by thermal expansion and by long supply routes.

Biochar - climate-positive, but with conditions
Well-made biochar from residues such as green waste or wood waste can indeed be climate-positive: The pyrolysis process generates excess heat that can be used for energy and sequesters CO₂ in the soil long-term. This sounds convincing - and it is, if the entire production chain is right.
But: This only applies to industrially produced, certified biochar from traceable residues with proven freedom from harmful substances. What the end customer actually gets in the bag at the garden center is difficult to verify. The climate calculation is only correct if the starting material, pyrolysis process, and transport are meticulously documented.

Zeolite - the most gentle method
Zeolite forms without human intervention - it is a natural volcanic mineral that has been stored in the earth for millions of years and is simply mined. No firing process at 1000°C, no thermal expansion, no chemical process. Mining, processing, and transportation cost energy.
Our raw material comes from eastern Slovakia and is processed in Austria - short distances compared to Greek perlite or clay from Eastern Europe. The tribomechanical pulverization process for BODENKRAFT ZEOLITH PUR is more elaborate than simple sieving, but a fraction of the energy required for expanded clay or perlite. And the result remains permanently in the soil - once incorporated, zeolite works for decades without renewal.

Sustainability comparison at a glance:

	Energy for production	Raw material availability	Climate balance	Durability in soil
Zeolite	✅ Low	✅ Abundant	✅ Neutral	✅ Decades
Perlite	⚠️ Medium + long transport routes	✅ Sufficient	⚠️ Negative	⚠️ ~5 years
Biochar	✅ Low (from residues)	✅ Biomass available	✅ Positive (only if certified)	✅ Centuries
Expanded clay	❌ Very high	⚠️ Raw material is becoming scarcer	❌ Negative	✅ Permanent

The great property comparison at a glance:

	Zeolite	Perlite	Biochar	Expanded Clay
Origin	Volcanic mineral (natural)	Volcanic glass (popped)	Carbonized biomass	Fired clay
Water storage	✅ Very good	⚠️ Low	✅ Very good	✅ Medium
Nutrient storage	✅ Very good (active)	❌ None	⚠️ Passive, only after loading time	⚠️ Low
Immediate effect	✅ Yes	✅ Yes	❌ No (weeks–months)	✅ Yes
Aeration/Drainage	✅ Good	✅ Very good	✅ Good	✅ Very good
Promotes soil life	✅ Very good	❌ Hardly any	✅ Good (if clean)	⚠️ Medium
Durability	✅ Permanent	⚠️ ~5 years	✅ Centuries	✅ Permanent
pH influence	⚠️ Slightly alkaline	✅ Neutral	✅ Neutral	✅ Neutral
Heavy metal risk	✅ None	✅ None	⚠️ Depending on origin	✅ None
Application	✅ Easy, clean	✅ Slightly dusty	⚠️ Black, very dusty	✅ Easy
Organic approved	✅ Yes	✅ Yes	⚠️ Quality dependent	✅ Yes
Ideal for	Beds, lawns, pots, raised beds	Houseplants, substrates	Long-term soil building (only certified quality)	Drainage, hydroponics

What fits when?

You have a vegetable patch or raised bed: → Zeolite is your first choice - immediate effect, safe for food plants, no heavy metal risk. Always combine it with AM+PLUS Active Microorganisms for maximum effect in the soil.

You have houseplants or potted plants: → BODENKRAFT ZEOLITH 0.5-1 mm as an admixture (10-20%), expanded clay as a drainage layer at the bottom of the pot. Also, add AM+PLUS Active Microorganisms and leonardite to the watering water - this keeps the soil life in the pot active and healthy.

If you want to improve your lawn: → Sprinkle and brush in zeolite. Perlite and biochar are less suitable here. Afterwards, pour in AM+PLUS – this additionally activates the soil under the lawn.

If you are building a raised bed or a garden for the long term: → Zeolite as a base, plus AM+PLUS microorganisms and good compost. Biochar can be added – but only if its origin, heavy metal-free status, and PAH-free status are fully verified. And, of course, also basalt rock dust and if the raised bed is in a southern location, water-storing pellets made from vermiculite are absolutely essential.

If you have hydroponics or want to drain pots: → Expanded clay as a substrate or drainage layer.

If you have acid-loving plants (blueberries, rhododendrons): → Perlite instead of zeolite – this does not raise the pH value. AM+PLUS microorganisms are still suitable.

Do I have to choose one?

No – and that is perhaps the most important thing in this article. These four materials are not competitors; they are complementary. And we would like to highlight one more supplement that is just as important as the mineral itself: active microorganisms.
Zeolite creates the structure – cavities, storage, buffer. But without active soil life, zeolite only operates at half power. Microorganisms are the ones that break down nutrients, transport them, and make them available to plants. That's why we always recommend combining zeolite with AM+PLUS Active Microorganisms.

A good substrate mix for a raised bed could look like this:

• 60% good compost soil
• 25% BODENKRAFT ZEOLITE 0.5-1 mm (nutrient buffer, water storage)
• 15% Perlite (aeration, drainage)
• AM+PLUS Microorganisms in the watering can – from the beginning and regularly

Conclusion

Zeolite, perlite, biochar, and expanded clay — all four have their raison d'être. But they are fundamentally different in what they do:

• Zeolite is the active storage – immediately effective, actively stores water and nutrients, safe for all plants and food cultivation. The universalist among soil conditioners.
• Perlite is the aerator – light, structure-improving, chemically neutral. Ideal as a supplement, less as a main product.
• Biochar is the long-term idea – interesting for soil building over decades, but only if quality, heavy metal-free status, and clean production are fully ensured. Not an immediate solution, and not without risk.
• Expanded clay is the classic – structurally stable, ideal for hydroponics and drainage, but not a nutrient store and energy-intensive to produce.

If you could only choose one? For most garden and pot situations, it would be zeolite – because it is the only one that actively buffers nutrients, works immediately, is safe, is sustainably produced, and simultaneously stores water and promotes soil life.
And the best zeolite is of little use without living soil. Therefore, the rule always applies: add AM+PLUS microorganisms.

Frequently Asked Questions (FAQ)

Which is better – perlite or zeolite?
It depends on what you need. Perlite primarily improves aeration and drainage – it is chemically inert and does not store nutrients. Zeolite can do both: It improves soil structure just like perlite, but also actively stores water and nutrients and releases them as needed. For most garden and potting applications, zeolite is therefore the more active and versatile choice. Perlite is particularly suitable where maximum drainage is paramount – e.g., for cacti, succulents, or orchids. For vegetable beds, raised beds, and lawns, zeolite is clearly superior.

Which is better – zeolite or biochar?
Zeolite works immediately – from the first watering, it stores water and nutrients and releases them in a buffered manner. Biochar takes weeks to months to charge and exert its effect. Zeolite is also safe for food plants – it is a pure natural mineral without organic starting materials. With biochar, safety heavily depends on the origin and production process. For immediate use in the garden, zeolite is the better choice. Biochar can be useful as a long-term supplement – but only from a certified, fully traceable source.

Which is better – expanded clay or zeolite?
For different purposes. Expanded clay is ideal as a drainage layer in pots and for hydroponics – it maintains structure, is stable, and prevents waterlogging. Zeolite can do this too, but also actively stores nutrients and water. In beds or raised beds, zeolite is significantly more effective than expanded clay. Combining both – zeolite in the soil, expanded clay as the bottom drainage layer in the pot – gives you the best of both worlds.

Can zeolite and perlite be used together?
Yes, and it is even a very good combination. Zeolite handles nutrient and water storage, while perlite ensures aeration and quick drainage. A proven mix for raised beds or potted plants: 60% compost soil, 25% zeolite, 15% perlite – plus AM+PLUS microorganisms in the watering can.

How long does zeolite work in the soil?
Zeolite is a mineral – it does not rot or degrade. Once incorporated, it remains active in the soil permanently. In contrast, perlite disintegrates into dust after about 5 years. Zeolite therefore does not need to be renewed regularly – a single initial treatment works for decades.

Can you use too much zeolite?
Zeolite is considered very safe to use. The recommended amounts (0.5-1 kg per m² in the garden, 10-20% in potting substrate) are guidelines – a little more won't hurt. The only exception: For acid-loving plants like blueberries, rhododendrons, or azaleas, zeolite can slightly raise the pH value – here, use sparingly.

Is biochar really sustainable?
Well-made biochar from residual materials can be climate-positive – it sequesters CO₂ in the soil long-term. But this only applies to industrially and certified manufactured products from traceable residues. Uncertified biochar can concentrate heavy metals and contain polycyclic aromatic hydrocarbons (PAHs). Without full proof of origin, biochar is not recommended for vegetable gardens.

Can zeolite be used as a drainage layer in pots?
Yes. A 1-2 cm layer of zeolite at the bottom of the pot works as drainage – with the advantage that zeolite simultaneously buffers nutrients and water instead of simply letting them run off. Even better: expanded clay as the bottom drainage layer, with a substrate mix containing zeolite above it.

Do I still need fertilizer after incorporating zeolite?
Yes. Zeolite is not a fertilizer – it is a nutrient store. It holds nutrients in the soil and releases them as needed, but it does not supply them itself. So you continue to fertilize, but need less, because less is leached out. And combined with AM+PLUS microorganisms, your fertilizer works even more efficiently.

What is the difference between BODENKRAFT ZEOLITE and BODENKRAFT PUR?
BODENKRAFT ZEOLITE (0.5-1 mm) is a natural zeolite granulate – ideal for incorporating into beds, raised beds, and lawn areas. Easy to handle, clean, and permanently effective. BODENKRAFT PUR is tribomechanically ground zeolite with a grain size of 100 µm – fine powder. The tribomechanical grinding process preserves the internal crystal lattice structure and thereby increases effectiveness. It is particularly suitable as a foliar fertilizer, for rapid soil activation, and for fine substrate mixes.

Sources

On Zeolite:

• Polat, E., Karaca, M., Demir, H., & Onus, A. N. (2004). Use of natural zeolite (clinoptilolite) in agriculture. Journal of Fruit and Ornamental Plant Research.
• Mumpton, F. A. (1999). La roca magica: Uses of natural zeolites in agriculture and industry. Proceedings of the National Academy of Sciences (PNAS).
• Ramesh, K., & Reddy, D. D. (2011). Zeolites and their potential uses in agriculture. Advances in Agronomy.
  
• Duenger-und-erde.de. Zeolite — Additive for garden soil. duenger-und-erde.de
• STEINKRAFT Zeolite Online Shop (2026). Correctly applying zeolite in the garden. steinkraft-naturerocks.com
• STEINKRAFT Zeolite Online Shop (2026). 7 mistakes when using zeolite in the garden. steinkraft-naturerocks.com
• Kraut & Rüben (2025). Soil conditioners: Advantages of zeolite in the vegetable bed. krautundrueben.de

On Perlite:

• FARBIO (2025). Using perlite for plants. farbio.com
• Gartenjournal.net (2025). Perlite or expanded clay — Differences and application tips. gartenjournal.net
• Samenhaus Gartenblog (2024). Perlite, expanded clay and other granules. samenhaus.de
• Nachhaltiges-bauen.de. Life cycle assessment of perlite. nachhaltiges-bauen.de

On Biochar:

• Swiss Federal Office for the Environment / FOEN (2022). Fact sheet: Biochar in Swiss agriculture — Risks and opportunities for soil and climate. bafu.admin.ch
• IfLS / Landwirtschaftliche Rentenbank (2022). Use of biochar in agriculture: Opportunities and challenges. ifls.de
• Bundesinformationszentrum Landwirtschaft (2024). What potential does biochar have for agriculture and climate? landwirtschaft.de
• terrABC / Hubert Würsch (2021). Pyrolysis fundamentals 3: Open questions / Risks. terrabc.org
• Fraunhofer Innolab (2023). TCR Pyrolysis — Heavy metals and biochar. websites.fraunhofer.de
• Wikipedia DE. Biochar. de.wikipedia.org
• GaLaBau Beschaffungsdienst (2024). Biochar: the new generation of sustainable soil improvers. soll-galabau.de
• Gaertner-und-florist.at (2025). Biochar in horticulture. gaertner-und-florist.at
• Keep it grün (2024). Biochar — everything you need to know. keep-it-gruen.de
• Ithaka Journal (2011). Opportunities and risks of biochar. ithaka-journal.net
• Deutsche Schreberjugend (2025). Statement on the article by the Federal Environment Agency on the private production of biochar. deutsche-schreberjugend.de

On Expanded Clay:

• Duenger-und-erde.de. Expanded clay — Substrate for drainage and hydroponics. duenger-und-erde.de
• Nachhaltiges-bauen.de. Life cycle assessment of expanded clay. nachhaltiges-bauen.de

General / Comparison:

• Schicker Mineral (2025). Climate-friendly gardening: How to bind CO₂ and store water. schicker-mineral.de
• COMPO (2024). Mineral substrate — ideal for houseplants? compo.de