Trichoderma harzianum is a typical soil fungus, widely known as an antagonist of plant pathogens. Isolates of this Trichoderma species are often found in nature as mycophiles, without evidence of association with any specific systematic groups of fungi.

The positive effects of T. harzianum on plants include both indirect stimulation of plant growth by displacing and suppressing the development of soil phytopathogens through the production of compounds that inhibit pathogenic microflora, and direct effects through the synthesis of various exometabolites by this fungus. These metabolites directly penetrate plants and influence plant immunity and intracellular biochemical processes. Proteins and carbohydrates accumulate in plants faster, and chlorophyll content in leaves increases. Furthermore, T. harzianum actively participates in the soil-forming process by converting plant litter cellulose into soluble organic matter, which is utilized by other soil-forming agents—saprotrophic fungi, bacteria, and actinomycetes.

The most active plant-beneficial properties belong to the T. harzianum strains G 30 VIZR (based on the biopreparation Trichocin) and VKM F-4099D (based on the biopreparation Sternifag).