Use clay granules correctly

Use clay granules correctly

the essentials in brief

  • Clay granules consist of fired clay balls (€ 20.95 at Amazon *) and can be used very well as a substitute for potting soil.
  • Alternatively, you can mix the material together with potting soil and thus improve the water storage capacity of the substrate.
  • Clay granules have a very high water storage capacity, which is why you have to water cultivated indoor plants less often.
  • However, there are some special features to consider when caring for these plants. Since clay granules do not contain nutrients, you need to regularly provide these plants with a special fertilizer.

What is clay granules?

clay granules

Clay granules, as the name suggests, are made from clay. This is a particularly fine-grained type of soil that is created by the decomposition of rock spades (again a collective name for various types of rock). Clay is considered to be a good water reservoir, a property that is further improved and optimized through the process of clay granulate production. To do this, clay is ground, granulated and then burned at extremely high temperatures of around 1200 degrees Celsius.

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During this process, the organic substances contained in the raw material burn, producing carbon dioxide. The gas in turn expands the granulate so that the typical round spheres are created. Clay granulate has a porous surface and is therefore able to absorb and store water. For this reason, the material is ideal as a sole or additional substrate for indoor plants, but also for other purposes. What you can use clay granules for and what you should pay attention to can be found in the following sections.

Types of clay granules

There are different types of clay granules, which differ in these properties:

  • Grit
  • pH and salinity
  • Suitability for plant species

Clay granules are available in different grain sizes, ie the spheres are different in size depending on the product. A grain size of 4/8 is suitable for most indoor plants, as the plant roots find the best hold here - the small balls with diameters between four and eight millimeters fill gaps well and leave only a few cavities. However, they only let a little air through, which is why you prefer to use a coarser grain size such as 8/16 for larger indoor plants.

There are also differences between the pH value and the salt content of the different products. Most clay granules have a pH of around 7 and are therefore suitable for most plants. If, on the other hand, you need a slightly acidic substrate for your crops, Seramis is well advised. With regard to the salt content, there are differences between the individual products between two and 920 milligrams per 100 grams of clay granules. If you want to hydroponically plant your indoor plants or cultivate salt-sensitive species, choose a product with less than 250 milligrams of salt per 100 grams of clay granules.

advantages and disadvantages


The most important positive property of clay granules is their ability to store water and gradually release it back to the plants as needed. Therefore, plants cultivated in this material have to be watered much less frequently. This table clearly shows the advantages and disadvantages of clay granules compared to conventional potting soil.

durable, usable again and againexpensive
good water storagedoes not contain any nutrients
ensures an even water supplyregular fertilization is essential
air permeableMoisture content cannot be seen or felt from the outside
prevents root rotWater level indicators are therefore indispensable
no fungus gnats and other pests that lay their eggs in soillight weight, fluctuates due to water absorption and release
clean and suitable for allergy sufferersLarger plants in particular threaten to tip over without being weighed down
does not mold


Which is why a water level indicator is indispensable when using clay granules

A water level indicator is a type of thermometer for the flower pot. However, this does not show you the temperature, but the water content of the substrate. Since, in contrast to potting soil, you cannot estimate the water content of clay granules by sight or touch, such a device is indispensable. All you need to do here is take a look at the display: if it is at “Minimum”, it must be poured.

What can clay granules be used for?

Clay granules are probably the most frequently used in the care of indoor plants, which is why we are introducing three relevant areas of application to you at this point. But there are also various possible uses in aquariums, terrariums, for roof greening or in pond construction.


With hydroponics, you only plant and care for your indoor plants in clay granules. However, it is not enough to simply replace the potting soil with expanded clay (€ 17.50 on Amazon *). On the one hand, the switch to hydroponics requires careful washing of the roots so that no earth remains; on the other hand, you need special planting systems. These usually consist of an inner and an outer pot. In the inner pot you place the plant in the substrate, in the outer pot, on the other hand, there is the water, which has to be topped up regularly together with the nutrient solution.

Conversion to hydroponics - Here's how

The conversion to hydroponics works as follows:

  1. Pot out the plant.
  2. Remove the earth. Rinse out any residue from the root ball.
  3. Shorten roots that are too long; brown (rotten) roots will also be cut off.
  4. Pour a layer of expanded clay into the inner pot.
  5. Put the plant on top and fill up the inner pot.
  6. Lightly tap the bottom of the table to fill any gaps.
  7. Place the inner pot in the planter.
  8. Fill in lukewarm water and do not forget the water level indicator.

Ball of earth in clay granulate - simplified hydroponics

It is less inconvenient to leave the root ball of the plants intact (and with soil). Instead, you simply put the plant to be repotted with the earthy root ball in a surrounding layer of clay granulate. Here the roots are practically embedded in the new additional substrate, but are still in the ground. The water level indicator should not be missing here either.

Drainage for indoor plants - mix clay granules with soil

clay granules

Alternatively, mix the clay granules with the potting soil to improve its water-storing properties or to guarantee an optimal supply of moisture. You have different options:

  • For pot drainage, pour a layer of expanded clay on the bottom of the pot.
  • This should be between two and ten centimeters thick, depending on the size of the pot.
  • Before doing this, place a pottery shard over the drain hole to prevent it from clogging.
  • Mix the potting soil with fine expanded clay balls.
  • You will need about a handful for a 15 to 20 centimeter diameter pot.

A water level indicator is not absolutely necessary in this case, but it can make it much easier for you to determine the right time to water.


Broken clay granules for pond plants

Instead of lining the garden pond with foil or using a pre-formed plastic tub, you can also use clay for sealing. Clay blocks made of moist material or broken clay granules (swelling clay) are suitable for this. The layer of clay on the pond floor should be between 10 and 20 centimeters thick, depending on the size of the pond.

Where can I buy clay granules?

"Plants need a good substrate to find support and to draw nutrients and water from it."

You can purchase clay granules either as a branded product (e.g. Floragard, Seramis or Dehner) or as a no-name product (e.g. own brands from DIY megastores with gardeners such as Obi, discount brands). Usual pack sizes contain between 2.5 and 50 liters of different contents, depending on what you intend to do. You can find larger quantities in special shops, such as those you need for waterproofing garden ponds.

frequently asked Questions

Is there a difference between expanded clay and clay granulate?

The terms expanded clay and clay granules both refer to burnt, reddish colored clay balls. So there is no difference in meaning between them, but there can be differences between the individual products and manufacturers - for example in terms of grain size or intended use. Another name for clay granulate is plant clay.

Can I completely replace the potting soil with clay granules?

Used correctly - as described in the article - clay granules can actually completely replace potting soil. Then, however, you have to consider a few special features when caring for your indoor plants, such as the fact that using it alone without a water level indicator does not work or you have to fertilize regularly. With a simple finger test, it is not possible to determine whether the plants need water in the case of clay granules. Since the material is also inorganic, it does not contain any nutrients. These must be fed in continuously.

Are clay granules toxic?

No, clay granules are usually not toxic. After all, it is a natural material that has only been burned and thus made structurally stable. Chemical additives are not added to most products. Even so, you shouldn't eat the material, that's not what it is intended for and would not do you particularly well - your body cannot digest it. Instead, the globules could remain in the gastrointestinal tract and lead to serious blockages there.


Quite a few resourceful houseplant gardeners came up with the idea of ​​using compostable cat litter (e.g. based on bentonite) instead of clay granules. Although this has very similar properties to expanded clay in terms of its water storage capacity, it is not suitable as a plant substrate due to the often very high pH value. The reason is the high calcium content of the material, whereas most house plants need a slightly acidic to neutral pH value for their well-being.