Structural material and gas exchange
Plant roots and useful microorganisms need sufficient oxygen to survive. However, CO2 is produced when organic matter is metabolized, and this also happens in the soil. This CO2 is toxic to soil life above a certain concentration. If the substrate or soil has an open-pored structure, the excess CO2 can escape and be reabsorbed by the plant. Likewise, sufficient oxygen can enter the substrate. To ensure this gas exchange in the substrate, structural material such as pumice or perlite is added. In addition to these, lava rock, rice husks or biochar are also used. As the name suggests, the purpose of structural material is to give the substrate or soil structure and prevent compaction. Perlite, pumice and the like also store moisture. They usually contain hardly any nutrients and, as rock, decompose very slowly.
Depending on the environmental conditions and the plant, one material or the other is more suitable.
Perlite has proven to be ideal for peat-based substrates in smaller pots that are not used beyond one cultivation cycle. They store moisture but have a high pore volume, making the substrate airy. They are very light, which is why they are often used in bags. However, this low weight also has disadvantages. If the cultivation period is longer, perlite is washed out by frequent watering. The result is compaction of the substrate. Gas exchange can no longer take place.
For Living Soil substrates that are designed to be used over many cultivation cycles and are also cultivated in larger pots or beds, pumice and lava rock are the better choice. Due to their slightly higher weight, pumice and lava rock are not washed out by watering and gas exchange is guaranteed.
Rice husks and spelt husks are made up of 80 percent silicate but are broken down by soil life over several cultivation cycles. This means that gas exchange is not guaranteed. The substrate becomes too compact and the roots are no longer supplied with sufficient oxygen.
In addition to their physical properties, perlite and pumice also differ on another level that is increasingly coming into focus.
The energy consumption in production
Perlite is made of obsidian, a common rock that requires a lot of energy to become perlite. The energy required to produce it and therefore the CO² footprint is about 4 times higher than that of pumice or lava rock, which is a volcanic rock that can be easily mined and already has all the properties of a good structural material.
The pumice we offer comes from the Eifel region and is therefore a regional product that does not require long transport routes.