How can earth be sintered

Advantages and disadvantages of clay granules as a water reservoir

More and more often, plants are placed in clay granules. The advantages of this substrate are obvious, because it is visually appealing, largely germ-free and easy to care for. The most important property of expanded clay, of course, is its ability to store water in large quantities. The granules slowly return the moisture to the roots and thus protect the plant from drying out as well as from excessive watering. The granulate has few disadvantages, some aspects have to be considered when maintaining it.

Why is clay granulate a strong water reservoir?

To understand why expanded clay can store large amounts of water, it is worth taking a brief look at the production of clay granules. This material is produced in an oven at extremely high temperatures. At approx. 1000 ° C, the surface of clay grains is sintered, i.e. made stronger. At the same time, gases escape from the interior of the granule - products of combustion of organic components in the clay.

The gases do not destroy the surface, but rather form microscopic pores in it and expand the clay grains. The result is granules with a solid but porous surface - an ideal water reservoir. During irrigation, the pores fill with water that can only escape slowly. Clay granules therefore create favorable conditions for successful

Plant culture.

Benefits of clay granules

It is no coincidence that expanded clay is so popular with hobby gardeners, because its advantages as a water reservoir are obvious. Here are the main ones.

  • Water storage in a class of its own. The granules of expanded clay are lightweights, a granule can store up to 0.6 times its volume in water. The water is well secured in the clay granulate and is only given back to the roots in smaller portions.
  • Clay granules allow large intervals when pouring and this is exactly where the greatest strength of this substrate lies. Even if it has not been watered for a few days, e.g. because of a vacation or business trip, a plant does not mind.
  • Waterlogging is no longer a danger. The common mistake of a hobby gardener is generous watering. Most plants do not like having "wet feet" let alone swimming in water. If too much water is poured regularly or if watered "in advance" before a longer absence, dangerous root rot threatens. In the worst case, the roots die and with them the plant. Thanks to the clay granules, the risk of waterlogging is largely averted, because water that cannot be immediately absorbed by the roots is stored in the granules.

Tip: Clay granulate does not provide 100% protection against waterlogging either, because its capacities are large, but ultimately limited. The water level indicator must therefore always be observed!

  • Free of germs and pests. Clay granules are an inorganic substance and therefore do not contain any nutrients. This means that this substrate does not form a breeding ground for germs or pests. Mold also rarely occurs on expanded clay. Thus, clay granules are healthy for the plant and usually look well-groomed and personable.

Disadvantages and problems of handling clay granules

As already mentioned, this substrate has few disadvantages for the plant culture, but if some aspects are not taken into account, a plant threatens to die.

A water level meter is compulsory.

Without this compact measuring device, it can never be said with certainty whether the plant needs water or whether it still has enough. The granulate usually looks deceptively dry, especially on the surface. It can easily appear that the plant is thirsty. So always take a close look at the display before watering.

Tip: Only add water when the display has really reached a minimum.

Easy is dangerous.

The expanded clay is very light when dry. Soaked with water, it is of course quite difficult. After most of the water has been used up by the plant, the granulate becomes lightweight again.

The problem: a large, heavy plant loses its grip and can even tip over.

Tip 1: The larger the plant and the pot, the coarser the granules should be. Several grades of this substrate are commercially available.

Tip 2: When filling the pot with granules, place some heavy stones on the bottom or mix the granules with sand. The heavy sand makes the substrate more stable, of course the plant should feel comfortable in sandy soil.

Don't forget to fertilize!

The granulate is neutral, i.e. this substrate lacks the nutrients that are essential for a crop. Watering alone is definitely not enough for the plant to thrive, especially if it is supplied with tap water (never use water directly from the tap, leave it to stand for at least a few hours at room temperature!) Therefore, adding fertilizer is vital. When choosing a fertilizer, make sure that it is also suitable for clay granules.

Tip: The granules naturally not only store the water, but also the liquid fertilizer. There is therefore a risk of over-fertilization - but too much fertilizer is just as bad for a plant as no fertilizer at all. It is better to fertilize at slightly larger intervals than stated on the packaging.


  • Can expanded clay improve the water-retaining properties of conventional potting soil?

Yes, clay granules can be mixed under the potting soil to loosen it up, provide better drainage and retain more water. By the way: A watering indicator (water level indicator) is also a good help here and shows whether there is a need for watering.

  • Do clay granules store less water over time?

Expanded clay is actually structurally stable and extremely durable. But every 3-4 years it is worth repotting a plant in fresh granulate, the "old" substrate can be used again after it has been thoroughly cleaned with hot water (without detergent!) And dried in the air.

  • Are there alternatives to clay granules as a water reservoir?

Yes, recently the so-called Geohumus has also been offered as a water-storing substrate. This soil additive can absorb considerable amounts of liquid and improve the soil function to a large extent. In contrast to clay granulate, Geohumus loses its water-storing properties after a few years.