The 4 Main Physical Properties of Potting Mix Components

As defined by Oregon State University- James Altland, Ph.D.

  1. a stability for root anchorage,
  2. a reservoir for nutrients,
  3. provide for an oxygen and gas exchanges for the roots,
  4. provide a space for root water up-take

How materials function together on a  mechanical level

If you use the identical potting soil mix in a small container as a larger container, the perched water table remains the same. See the example figure below. This is why OST has different mixes for a small pot for cuttings, a different mix for a 1 gallon pot for growth and yet a different mix for for a 5 gallon pot for the flowering stage.


Formulating a Potting Mix For Every Purpose

“It is possible to formulate a growth medium for a specific container size, growth environment, management intensity and the plant’s requirements. It has been noted that container depth directly affects the percent of the growth medium that is filled with air at container capacity. A growth medium for plants grown in a greenhouse, where control of the moisture level is possible, can have a greater water-holding capacity than a medium for plants exposed to natural rainfall distribution.

University of Florida Extension Service

A good media needs a combination of larger particles that bind the entire potting mix together to hold the plant in place. OST’s root anchorage is affected by peat moss, coco fiber, Macadamia shell Biochar and residual palm leaf fibers which are added before composting.
When using BioChar in combination with the a 8 ingredient Organic Compost, you have a nutrient reservoir unlike most. BioChar is layered and porous providing a large surface area for cation exchange. The positively charged anions attract the negatively charged cations of the nutrients. This is especially effective with nitrate.
Container medias must have sufficient pore spaces to allow free movement of gases.  Plant roots constantly undergo respiration.  Respiration is a cellular process that burns sugars to create energy (sugars are generated by photosynthesis in leaves).  Cellular respiration consumes oxygen and releases carbon dioxide (CO2) as a byproduct.  There must be sufficient pore spaces in the media for plant roots to acquire oxygen and expel CO2.  This tradeoff between CO2 and O2, called gas exchange, is an often-overlooked aspect of selecting container media.  After containers are completely saturated and allowed to drain, 10 to 30% of the container volume should be air space for gas exchange.
Container media has to retain water for plant roots.  All medias retain water, some more than others.  For example, peat retains a great deal of water while sand retains very little.  Peat moss and coco fiber can be purchased in a wide spectrum of particle sizes, with smaller particles holding more water than large particles.  After containers are saturated and drained, 45 to 65% of the container should be filled with water. Of water held by container media, some is available to plants and some is not.  Through physical processes called adhesion and cohesion, water is bound to media to form a thin film over particle surfaces.  This thin film of water is generally unavailable to plant roots.  Available water content is the portion of the water in a container accessible to plant roots.


The 4 Main Nutritional Properties of Organic Mix Components

  1. The quantity of available major and minor elements
  2. The quality of the microorganism community
  3. The ability to retain and store the elements
  4. The ability to release elements when needed


The material list you see in our organic substrates have been chosen to accommodate both the nutritional concern as well as the physical. How the materials work together nutritionally echos the symbiotic relationship we find in nature. This is what true organics is all about. Organics is much more than simply  not applying chemicals in your growing scheme. More than that, organics in nature reflect the symbiosis of soil, plant and microorganisms for the healthy state of all three. So symbiotic organics is what we will be talking about here at OST.

The materials we used in Creating a Natural Symbiosis

  1. Inert Mediums of palm leaf fibers, peat moss and coco fiber
  2. BioChar of Macadamia nuts and rice hulls
  3. Organic Compost of palm seeds, ground bone meal, shrimp heads, chicken manure, rice hearts, molasses and Beneficial Indigenous Microorganisms (BIM) as well a: Levaduras: Saccharomycescerevisieaevar. ellipsoides y Rhodotorula glutins, Bacterias lácticas: Lactobacillus lactis y Streptococcus lactis, Cellulose decomposing microbs: Cytophaga spp; Trichoderma reesei

The above 3 categories of materials we use in all our potting mixes for all sizes of pots. In general terms, the difference between a potting mixes for small, medium and large pots, is the size of the inert particles and percentage of each component.

Inert Medium

The inert medium we use is a mix. First there is an abundant amount of palm leaf fibers residual from the fresh palm leaves added as a nitrogen enhancer in the composting. Peat moss and coco fiber are also added. All three are considered inert but can effect indirectly the nutritional uptake of plants. I am talking about not only their physical structure, but their pH as well. Peat moss carries a low acid  5pH while coco fiber is neutral with a 7 pH. The ideal potting mix will be close to a 7 pH. Therefore when considering how much peat moss or coco fiber for our inert component, we need to consider what pH is in the other components. Both peat moss and coco fiber have similar physical properties.

Peat moss’s low pH of 5, together with the Biochars low pH, if added in the right combinations, offsets and balances the very high alkaline pH of the organic compost ingredients. In the final analysis, this places the substrate mix at a mild pH of between 6.8 and 7.1.


Our Biochar is designed and made with pyrolysis at low temp and low oxygen levels, over the coarse of a two day resident time. This ensures large pores to accommodate fungal and beneficial bacterial microorganisms, providing a Refugio from bacterial and fungal grazers. At low temperature production many nutrients remain in the biochar pores to not only feed the microorganisms but the plants as well.

Organic Compost

OST’s organic compost is listed below. It was created using 8 different ingredients. All were put together for the feeding of a specially created community of over 10 different microorganisms. Some of these mini-workers are indigenous to Costa Rica, the country of residence for Organic Soil Technology’s endeavors.. These microorganisms are various aerobic bacterias including the very important Lactobacillu and a collection of mycorrhizal and trichoderma fungi.

  1. Bone meal
  2. Chicken manure
  3. Shrimp Heads
  4. Palm seeds & leaves
  5. Molasses
  6. Semolina which is the inner grain of fresh rice
  7. BioChar of macadamia shells and rice hulls
  8. Beneficial Indigenous Microorganisms (BIM) as well a: Levaduras: Saccharomycescerevisieaevar. ellipsoides y Rhodotorula glutins, Bacterias lácticas: Lactobacillus lactis y Streptococcus lactis, Cellulose decomposing microbs: Cytophaga spp; Trichoderma reesei