Humic and Fulvic Acids: What They Do and Where MCT Fits In

Healthy growth depends on more than which nutrients you supply. It also depends on how effectively plants can access and use them. Humic and fulvic acids can influence root development and nutrient availability. In my work as a plant resilience specialist, I saw interesting changes in root growth. Those observations also led me to investigate Micro Carbon Technology (MCT).

What do humic and fulvic acids do?

Humic and fulvic acids form as organic material decomposes and undergoes further transformation, including microbial processes. They belong to the complex group known as humic substances, found in soils and compost. Concentrated formulations are also used in horticulture.

Humic acids have chemical groups that interact with nutrients such as iron, calcium and magnesium, affecting their retention and availability in the root zone. Fulvic acids generally comprise smaller, more soluble fractions and can interact with minerals too. Depending on their composition, humic substances can also affect microbial activity and plant physiology.

Research has shown that certain humic preparations stimulate lateral roots and root hairs. Auxin-related signalling and proton-pump activity are among the processes involved, as described by Canellas (2015) and Shah (2018). A 2026 meta-analysis of 111 publications found that biostimulants improved several root traits on average, with humic acids showing particularly consistent effects. Results still depend on the product, crop and growing conditions.

Where does Micro Carbon Technology fit in?

MCT uses processed, relatively small carbon-rich organic fractions. Their composition can affect solubility and interactions with mineral nutrients. But smaller fractions do not, by themselves, prove faster or more efficient nutrient uptake.

This diagram illustrates a conceptual size comparison; it does not show measured molecular dimensions or nutrient uptake.

A Lisianthus trial: around 30% more dry matter

At a Lisianthus nursery, the soil was steamed after each crop cycle because of autotoxicity. Both the MCT-treated crop and the untreated control grew in steamed soil and received the same fertiliser programme. The addition of MCT was the only difference between the treatments. We observed around 30% more dry matter in the MCT-treated crop than in the control.

Steaming can make nutrients from existing soil reserves more available, alongside the fertiliser supplied during the crop. But this applied to both treatments and therefore does not explain the difference between them. Because adding MCT was the only difference between the treatments, the higher dry-matter production in this trial can be attributed to the MCT treatment. This points to improved uptake or use of nutrients from the fertiliser and soil reserves, although these processes were not measured separately.

Foliar trials: more compact plants under limited growing height

In separate foliar growth-regulation trials, we applied MCT-based products together with calcium and silicon. The treated plants remained shorter, with less stem elongation. For home growers using lamps in a space with limited height, that compact growth is a practical advantage.

In ornamental horticulture, reduced stretching and tissue dry-matter content are relevant to crop quality and keeping performance. Whether this combined treatment changes dry-matter percentage or THC concentration in cannabis has not been established. The trials also did not isolate MCT from the effects of calcium and silicon: the observed growth response belongs to the combined treatment.

For the different application routes, see foliar feeding versus root-zone feeding.

Humic substances, Bacillus and MCT: complementary possibilities

Humic and fulvic acids need not compete with MCT. Studies of humic substances combined with plant growth-promoting bacteria, including Bacillus, have reported benefits for roots or nutrient use in certain systems (da Silva, 2021).

Micro Matrix follows a related formulation approach: it combines Bacillus strains with organic components, including fulvic and humic fractions according to the product composition supplied for this project. Results from other formulations cannot establish the performance or synergy of these particular tablets.

For home growers, strong early root development matters, especially with autoflowers, whose vegetative phase cannot simply be extended after a slow start. Better nutrient use might also allow a lower nutrient-solution EC where excessive salinity limits water uptake. The practical test is whether the crop maintains adequate nutrition and growth at that lower EC, not whether a product can simply be added. See also EC, water availability and nutrient uptake.

References

Canellas et al. (2015). Humic and fulvic acids as biostimulants in horticulture. Original reference PDF. DOI: 10.1016/j.scienta.2015.09.013.

Shah et al. (2018). Humic Substances: Determining Potential Molecular Regulatory Processes in Plants. Original reference PDF. DOI: 10.3389/fpls.2018.00263.

Wang, Y. et al. (2026). Biostimulant Applications Improve Crop Root Morphology in Agricultural Systems: A Global Meta-Analysis. Agronomy, 16(7), 743. DOI: 10.3390/agronomy16070743.

Salehi, H., Savy, D., Rao, M.A. & Lucini, L. (2026). Humic substances for abiotic stress resilience: current knowledge and perspectives. Plant Physiology and Biochemistry, 237, 111490. DOI: 10.1016/j.plaphy.2026.111490.

Gollenbeek, L. & van der Weide, R. (2020). Prospects for humic acid products from digestate in the Netherlands: quickscan. Wageningen Plant Research, WPR-867. DOI: 10.18174/541280.

da Silva, M. S. R. A. et al. (2021). Humic Substances in Combination With Plant Growth-Promoting Bacteria as an Alternative for Sustainable Agriculture. Frontiers in Microbiology, 12, 719653. DOI: 10.3389/fmicb.2021.719653.

Hofland-Zijlstra, J. (2023). Wat is de rol van humus- en fulvinezuren in biostimulanten? Vakblad Onder Glas, 26 januari 2023. Artikel.