Posted on by Jason G

Humic Acids 101

In order to talk about humic acids and what they do for plants and growing substrates, we must first talk about humus.

If we analyze top soil for example, there is 45% mineral content 50% air & water content, 2% plant & animal remains, 2% Humus and less than 1% living organisms (bacteria, fungi & insects).

The formation of humus is a continuous cycle, breaking organic matter down into basic components by the decomposers, insects, fungi and bacteria. 

Decomposition is continuous, alongside it, is the slow degradation of rocks and minerals caused by external factors like natural weathering and rock eating organisms named lithotrophs.

The second part of this cycle is the reformation of the broken down particles into a variety of chemical compounds, collectively these compounds are called humus. Eventually these compounds break down further into molecules that are very chemically stable and resistant to further decay.

These molecules are broken down into three forms;

  • Humin
  • Humic acids
  • Fulvic acids


Now that we have a basic understanding of the origin of humic acids we can now we can talk about their relationship with plants. Humic acids contain high amounts of carbon which directly feeds microbes, in turn improving soil ecology.

Humic acids benefit gardeners because they act as a natural chelator of other elements.

“Chelate” Allows complex molecules to bind to other ions.

Molecules of humic acids are negatively charged because they have lost positively charged hydrogen ions, this creates spaces on the molecules where positively charged particles, zinc, iron, copper & manganese can attach. The roots systems of plants are also negatively charged but have a much greater charge than humic acids do, as a result the humic acid compound is drawn to the root, positively charged ions then leave the humic acid molecule in favour of the root. The plant in turn can now use these micro elements for growth and reproduction.

Positively charged ions are referred to as cat-ions, is the measurement of a substrates ability to hold onto these cations, this process is called cation exchange capacity (CEC), mineral composition of soils is made up of various combinations of sand, silt & clay. Clay particles have a strong negative charge, soils comprised with large amounts of clay have a high CEC, which reduces leaching of the positively charged cations. Sandy soils have a low CEC meaning some elements are more easily flushed through the roots zone, because of humic acids ability to chelate cations, humic acids may have the ability to raise the CEC of soils and other substrates, allowing more readily available elements available to the plant, in turn making fertilizer applications more efficient, for this reason it is advised that you incorporate humic acids into your fertilizer regime.

References: ecofarm, Omnia nutrition, Down to earth ferts