There’s a lot of focus these days on grow mediums, and one common misconception for new growers centers upon soil and soilless mixtures. To start, real Earth topsoil is rarely used indoors anymore. Still, people refer to soil-replacements as soil, creating some confusion among newer growers. In reality these mediums are artificial soils – or soilless mediums.
Soilless mediums are mixtures that look and feel almost identical to real soil, but are usually peat- or sphagnum-based. These mixtures also have added organic amendments such as coco-coir, perlite or wood chips to help aerate the medium and retain moisture for plants. They also sometimes have mild organic nutrients, beneficial microbial agents, or mycorrhizae (fungi) added in for better plant health.
The primary difference between soil and soilless mixtures comes down to their ability to retain water, oxygen and nutrient ions. These molecules all have electrical charges that help the root system absorb them as needed. These charges are often referred to as the CEC or “cation exchange capacity” (also referred to as EC, or electrical conductivity).
In the same way, grow mediums also have electrical charges. These charges in the medium will dictate how much nutrient and minerals the root system can absorb. In real soil, humus and certain other organic particles have high electrical charges or CEC. This means that the soil does not want to easily give up their minerals or moisture molecules to the plant.
As real soil dries out, it will retain water even more tightly. As plants need more water, soil begins to hold onto more of it and the plant must use extra energy to absorb it. This is not the case with soilless mediums.
Peat, sphagnum or coco-coir mixtures create soilless mediums that have extremely different CEC levels. In fact, most of them are inert, with zero CEC. This means that nutrients, water and gases such as oxygen (remember, the roots breath in O2, while the plant above ground breathes in CO2) are more readily available for uptake by the roots when the plant calls for them. It also means the plant will utilize more of what you feed your medium, converting nutrients and water into sugars during photosynthesis. Better uptake in the root zone results in better yields, as well as more resin and terpenoid production (i.e., higher potency and better flavor).
Best Uses for Soilless Mediums
While soilless mixtures offer easy passage of nutrient solutions to the root system, this loss of buffering can be dangerous for grow systems that use heavy doses of nutrients. Still, these mediums offer better buffering than most hydroponic mediums such as Rockwool or clay-pellets.
Because of this, soilless mediums are generally not recommended for big hydro set-ups such as flood-and-drain tables – not to mention, the medium is too unstable and fluid for such a system. Instead, these artificial soils are best suited for top-feed systems that utilize separate containers for each plant site.
Top-feed systems generally use stake emitters that plug easily into soilless mediums. These emitters may be drip-emitters or spray-emitters, drawing water from reservoirs like any hydroponic system would. Soilless mixtures are also great for smaller gardens at home where growers hand-water daily.
These mediums also over great flexibility and allow growers to customize their blends with various amendments. Many advanced growers and commercial operations tend to chose soilless mixtures as they can custom order mixtures or create their own easily at industrial facilities. Popular store brands of soilless mixes include Sunshine, Pro-Mix, Fox Farms and Roots Organics.
Thanks for reading everyone and remember: Grow… And help the world grow, too!