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Have you found styrofoam in your potting soil? You can find out what the little white balls are all about here.
What's that? You have just bought an expensive herbal soil, but when you open the bag, you immediately notice small white balls. White, round and light? That can only be styrofoam! And you don't want plastic like that in your bed. No reason to worry: the white beads are not the well-known packaging material, but perlite, a special type of rock. And this is not at all unwelcome - it even helps our plants feel more comfortable in the substrate.
Perlites in potting soil and their benefits
The rock perlite, which is mainly mined in opencast mines in eastern Europe and the Mediterranean region, does not just find its way into the plant substrate by chance. Under certain conditions, the white parent rock is formed from volcanic lava. The volcanic rock has to be burned at high temperatures (800 to 1200 °C) so that the rock gets its useful structure for the potting soil. The water contained in the raw rock causes an explosive popping up, which leads to the porous structure of the well-known aggregate for substrates. This process is similar to turning corn kernels into popcorn. The increase in volume that perlite experiences as a result of the heat is remarkable: the bloated rock can be up to ten times larger after the firing process. By the way: In order to distinguish the porous mineral in the substrates from the parent rock perlite, experts call it expanded perlite.
Thus, expanded perlite in the potting soil − even if it looks like it − is not artificial and certainly has nothing to do with styrofoam. The porous structure that the parent rock gets due to high temperatures is the secret behind its use in potting soil: Thanks to a pore volume of up to 95%, it ensures excellent aeration of the substrate - the small white stones are the ideal soil conditioner. It also stores water in its fine pores and ensures thatexcess moisture can drain off better: waterlogging no longer has a chance. Perlites are real heroes, especially for plants with sensitive roots or cuttings that have yet to develop their roots, which is why they are mainly found in potting soil or herb soil.
Another advantage - especially during propagation - is that expanded perlite is sterile due to the high temperatures and thus the risk of infection of the small, sensitive plants is reduced. In addition, the mineral material is very weather-resistant, so that it only degrades very slowly. This in turn guarantees a "structurally stable" potting soil: The substrate does not collapse and consequently compact as quickly as is the case with organic materials such as rice husks, which are also intended to improve the air capacity in the soil.
Due to its good physical properties, expanded perlite is used for:
- Improvement of air capacity and structural stability in substrates and potting soil
- Higher rooting success when propagated by cuttings
- Reduced risk of waterlogging in long-lived potted plants and moisture-sensitive crops
- Incorporation in soils prone to waterlogging for loosening (also in beds)
- Use as thermal and acoustic insulation material in house construction
Perlites are often used in soil as an environmentally friendly substitute for peat. You can find out what other alternatives to peat there are in this article.