Humic acid is a group of complex organic compounds formed during the decomposition of plant and microbial material. It is one component of humus, the stable organic matter found in soil and compost. In gardening and container growing, humic acid products are used to improve nutrient retention, increase cation exchange capacity, and support root-zone microbial activity.
Humic acids can help bind nutrients in the substrate, reducing leaching and making some minerals more available to plant roots over time. They may also improve soil structure in mineral soils by increasing aggregation and water retention. In container media with little natural organic matter, such as peat- or coco-based mixes, humic acid is sometimes added as a soil amendment or liquid supplement.
Humic acid is not a fertilizer because it contributes little direct nutrition. Its effects depend on substrate composition, existing organic matter, watering practices, and fertilization levels. Commercial products are commonly derived from leonardite, compost, peat, or other decomposed organic sources.
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