One of the major decisions hydroponic growers have to make is which growing medium, or substrate, to use for their grow. The selection of your growing media should depend on your growing technique, as different types of media react and perform differently depending on the hydroponic system and growing conditions. This article outlines three of the more popular mediums: expanded clay aggregate, rock wool, and perlite.
Types of Growing Media
Expanded Clay Aggregate
Expanded Clay aggregate, which is great for deep water culture, is an awesome medium for growing hydroponically This medium benefits from being completely inert, pH neutral, and contains no nutrient value that could affect a well controlled grow. Due to this, baked clay pellets make the perfect grow medium for systems in which nutrient levels are tightly controlled in the nutrient solution.
The baked clay pellets start out as simple clay. The clay is shaped into round pellets and then fired in a rotary kiln at 1,200 °C (2,190 °F). The intense heat cause the clay to expand into a porous, rigid, light weight state that benefits from its ability to resist compaction over time. Expanded clay aggregate is also considered an ecologically sustainable and recyclable, reusable growing medium.
Preparing the medium for reuse after a grow is easy, simply wash the medium in a solution of white vinegar, and either hydrogen peroxide or chlorine bleach. After washing the medium be sure to rinse it thoroughly to avoid contamination of the system. It should also be mentioned that reused expanded clay aggregate some times is regularly infiltrated by the roots of the previous plan, which may affect the next growing environment.
Rock wool or mineral wool is one of the most commonly used hydroponic growng mediums.Rock wool is also inert, pH neutral, and is suitable for both recirculating and run to waste systems. Rock wool starts as molten rock, basalt, or slag that is then spun into filament fibers that is then bonded into a form of medium capable of capillary action.
This allows the medium to resist most of the degradation caused by microbiological action common in hydroponics systems.One of the advantages of rock wool as a hydroponic growing medium that promote its efficiency as a commercial hydroponic substrate is that most rock wool is a completely non-hazardous, non-carcinogenic material. Rock wool is also light weight, stores easily, and is environmentally friendly.
Due to perlite low density and relatively low price (about US$50 per tonne of unexpanded perlite), many commercial applications for perlite have developed including its use as a hydroponic growing medium.
Perlite is a volcanic rock that has been heated into expanded glass pebbles. Perlite can be used loosely or in plastic sleeves immersed in the water. It is also commonly used in potting soil mixes to decrease soil density. The perlite material is a fusion of obsidian, granite, pumice, and basalt that is naturally fused at high temperatures and pressures inside the earth, undergoing what is called “Fusionic Metamorphosis”.