Using expanded clay correctly: tips for gardening, construction & hydroponics

Expanded clay - small balls, big effect. Anyone who loves plants should know it. Whether as a saviour against waterlogging, a helper for sensitive roots or a secret weapon in raised beds: expanded clay is a real all-rounder - and completely underestimated. In this blog, we'll show you what's behind the fired clay, how to use it correctly and where you can get it best. Whether for the garden, houseplants or hydroponics - here you'll find out everything you need to know.

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What is expanded clay actually - and what is it good for?

At first glance,expanded clay looks like a pile of small, brown marbles - inconspicuous, almost boring. But if you take a closer look, you will soon realise that there is more to these clay balls than meets the eye. Expanded clay is made from natural clay that is fired at over 1,000 degrees Celsius. The material literally expands due to trapped gases - similar to popcorn. The result is light, porous balls with a hard outer shell. And it is precisely this structure that makes expanded clay so versatile.

Where is expanded clay used?

Most people know it as a substrate for plants, especially in hydroponics or as a drainage layer in flower pots, but expanded clay can do much more:

• In horticulture, it provides airy, well-drained soil and prevents waterlogging - which is particularly valuable for sensitive roots.

• In house building, it is used as a lightweight aggregate in concrete or as an insulating material - lightweight, fireproof and mould-resistant.

• In decoration, it is often used as a design element in modern living concepts - minimalist, natural, functional.

In short: expanded clay is a real all-rounder - robust, reusable, environmentally friendly and quite underrated. No wonder it is constantly in use in so many areas without you really noticing it.

Expanded clay in the garden: how it works with drainage, substrate & co.

Anyone who has ever seen the water standing in the bed after a heavy downpour or pooling at the bottom of a flower pot knows that waterlogging is the arch enemy of healthy plant roots. This is exactly where expanded clay comes into its own - not just as a pretty gap filler, but as an active problem solver.

In the garden, expanded clay is valued above all for its open-pored, air-permeable structure. The clay pellets store water, release it slowly and at the same time ensure that excess moisture can drain away easily. Sounds simple, but it's brilliant - especially for sensitive plants or heavy soils.

This is how you can use expanded clay in the garden:

• As a drainage layer in planters: simply add 2-5 cm of expanded clay under the soil - this will prevent waterlogging in the pot or balcony box.

• In raised beds: Add expanded clay to the bottom of the bed before the soil is added - for better aeration and moisture management.

• For mixing with potting soil: A mix of soil and expanded clay makes the soil looser and more airy, especially in loamy or very dense soils.

• As a mulch layer: A layer of expanded clay on top of the soil keeps the moisture in the soil for longer and protects it from drying out.

• For herbs and Mediterranean plants: Rosemary, lavender & co. love dry feet - expanded clay is almost mandatory here.

• As a soil conditioner for heavy soils: Simply bury it or work it in when digging - for better soil structure in the long term.

A little practical tip: Although expanded clay is not biodegradable, it is extremely durable. If you don't throw it away in the compost at the end of the season, you can simply rinse it off and reuse it - this saves money and protects the environment.

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Houseplants love expanded clay - especially in combination

Indoors is where it gets really exciting: when plants in the home turn yellow, the soil turns mouldy or fungus gnats spread, it is often due to watering behaviour. Either too much, too little or simply the wrong substrate. And this is exactly where expanded clay comes into play as a good roommate: inconspicuous, easy to care for and always there when it matters.

Expanded clay shows its strengths particularly in combination with soil or as a pure hydro substrate - and not just for professionals, but also for anyone who likes things to be uncomplicated.

How you can use expanded clay for houseplants:

• As drainage in the flower pot: A layer of expanded clay at the bottom of the pot prevents roots from standing in water - this drastically reduces the risk of root rot.

• Mix with soil: A mixture of soil and expanded clay provides more structure and better aeration, especially for plants that prefer airy conditions (e.g. succulents or palms).

• As a pure substrate in hydroponics: Here, expanded clay completely replaces the soil. Many plants thrive wonderfully in a planter with a water level indicator - without any soil and with significantly fewer pests.

• As a top covering layer: A thin layer of expanded clay on top of the soil not only looks neat, but also prevents mould and fungus gnat infestation.

• During relocations or breaks in care: Plants that have to do without water for longer periods benefit from the expanded clay storing moisture and gradually releasing it.

Particularly practical: expanded clay is pH-neutral, does not mould and does not store fertiliser residue - a real haven of peace for stress-stricken roots. And if you're wondering whether this really works: yes, even demanding plants such as alocasia or calatheas will thank you for switching to a more permeable substrate with healthier growth and less drama.

Expanded clay for Monstera, hydroponics & co.: special cases at a glance

If plants were personalities, the Monstera would clearly be the hip city dweller with tropical roots. Beautiful, sensitive and a bit peculiar - especially when it comes to their substrate. This is precisely why many plant lovers swear by expanded clay for Monsteras (and similarly sensitive houseplants): either as drainage, in a soil mixture or completely in hydroponics.

Expanded clay not only helps against waterlogging, but also against common indoor problems such as mould or root rot, and makes care more predictable - especially if you don't get around to watering for a few days.

Possible applications of expanded clay for special indoor plants

Plant	Recommended application	Why expanded clay makes sense
Monstera	Drainage + soil mix or pure hydroponics	Prevents root rot, improves air circulation at the roots
Orchid	Mix expanded clay with some bark	Provides an airy, loose substrate that dries quickly
Ficus	Drainage layer + soil mixture	Reduces the risk of overwatering
Cactus & succulents	Mix expanded clay with mineral soil	Increases permeability, prevents waterlogging
Alocasia/Calathea	Expanded clay in hydroponics or soil mix	Airy roots = less root rot, better nutrient absorption
Hydroponic plants	Pure expanded clay culture with water level indicator	No dirt, easy care, even water distribution

Important: Expanded clay alone does not contain any nutrients - so anyone working with hydroponics or permeable substrates should fertilise regularly. A liquid fertiliser in the irrigation water is particularly useful for heavy eaters such as Monstera or Ficus.

What also helps: Rinse the expanded clay well before using it for the first time - this will remove dust and any residue. Then you can start moving your plants!

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Buying expanded clay: OBI, Thomas Philipps or online?

When it comes to buying expanded clay, the choice today is greater than ever - and also a little confusing. In DIY stores it is often found between potting soil and clay granules, at discounters such as Thomas Philipps it is sometimes found seasonally next to balcony boxes, and online? There's everything - from fine hydroclay to XXL balls for raised beds.

But where can you get the best quality at the best price and when is it worth stocking up?

Here is a brief overview to make your decision easier:

Comparison: Buying expanded clay - suppliers & differences

Supplier	Price level	Packaging units	Special features	Ideal for..
OBI / Bauhaus	Medium	5-50 litres	Mostly coarse-grained, own brands also available	Garden, raised beds, large pots
Thomas Philipps	Inexpensive	5-10 litres	Seasonal goods, occasionally on the special offer shelf	Price-conscious hobby gardeners
Amazon / online shops	Variable (from cheap to premium)	1-50 litres or more	Large selection of grain sizes, organic expanded clay also available	Houseplants, hydroponics, special requirements
Garden centres / plant markets	Medium to high	2-25 litres	Advice possible, often high-quality branded products	Demanding plant lovers
Discounters (Lidl, Aldi)	Very favourable	Usually small quantities (3-5 litres)	Only seasonal, quickly sold out	Occasional purchase, beginners

Tip: Pay attention to the grain size when buying. A fine expanded clay (4-8 mm) is usually suitable for houseplants, while a coarser version (8-16 mm) can be used for gardens or raised beds - it is more stable and better suited for larger quantities of water.

Another plus point: Expanded clay can be stored forever, so if you get a good deal, you can take a few more bags with you - the balls won't lose their shape or function.

Alternatives to expanded clay - when are they really worthwhile?

As practical as expanded clay is, it is not the ultimate solution for everyone. Some are bothered by the production process (keyword: energy consumption), others are simply looking for more regional, cheaper or more natural alternatives. And yes - there are alternatives. The only question is: can they really keep up?

A classic among expanded clay substitutes is pumice. Just like expanded clay, it is porous and light, but a volcanic rock - i.e. not burnt, but naturally formed. It scores with a similar structure, but is often a little more expensive and harder to obtain. For cactus lovers and succulents, however, it is definitely worth considering.

Then there's perlite - small white beads of foamed volcanic glass that are ideal for adding to soil. They are extremely light, improve air permeability and store water. However, they are less suitable as a drainage layer as they float and easily come to the surface when watering.

Another option is lava granules, which look similar to expanded clay, but are much heavier and have a sharper edge, which can be an advantage in the garden (keyword: stability in the soil), but a disadvantage for houseplants - especially with sensitive roots.

If you prefer a completely natural approach, you can use wood chips or coconut fibres. These are biodegradable, have a soil-improving effect and are great for mulching or loosening the soil. But beware: they decompose over time, which can reduce the oxygen in the soil - so they are not a real alternative to expanded clay for permanent drainage.

Conclusion: Expanded clay is difficult to replace when you consider its longevity, structure and flexibility. For selective applications, a change can make sense, especially when it comes to sustainability or specific plant requirements. But if you want to be on the safe side - whether in a pot, bed or raised bed - expanded clay is the way to go.

Conclusion: Why no green home should be without expanded clay

Whether in a flower pot on the windowsill or in a raised bed on the patio - expanded clay is one of those helpers that you discover once and never want to do without again. It looks inconspicuous, but what it does for plants and soil is enormous: better aeration, less waterlogging, healthier roots - and all without much effort or care knowledge.

Particularly charming: expanded clay is reusable, odourless and extremely durable. If you buy a bag once, you can use it for years. And even if something goes wrong or you have to re-sort the balls - they are very forgiving and retain their shape. No comparison with perishable soil mixes or cheap fillers.

Whether you're growing a demanding monstera, sprucing up your raised bed or simply want to arm your houseplants against fungus gnats - expanded clay is always a good idea. And the best thing is that you don't need to be a gardening pro to use it properly. A little research, a little trial and error - and the rest almost takes care of itself.

So if you love plants, sooner or later you should have a few of these brown miracle balls in the house. Your greenery will thank you - with vigorous growth, healthy roots and significantly less drama.