What is Humic Acid and How Does It Benefit Your Garden?

Humus is considered the holy grail of garden soil. This rich, dark substance is valued for its fertility and its ability to radically improve soil structure. As one of the components of humus, humic acid can be added to native soil to improve plant health and production while enhancing soil composition and water absorption.

Humus is the result of many years of decomposition. As animals and plants die and return to the ground, they break down with the help of beneficial organisms and microorganisms. Humus is simply organic material that has reached a point where it can no longer decompose. It is considered an extremely stable substance, due to the nutrients and compounds within it that resist decomposition. Humus is made up of humic acid, fulvic acid, and humins.

At EarthMix, we add humic acid to many of our garden soil mixes and amendments. Humic acid benefits your garden in a number of ways. It makes nutrients more available to plants, detoxifies garden soil, fosters a rich and living soil microbiome, and improves soil structure and fertility over time.

Relatively speaking, humic acid is a fairly large and complex molecule. One of the most important functions that humic acid performs is called “chelation.” The root of this word, “chele” derives from the Greek word for “claw,” and refers to the pincer-like claws on crustaceans (think lobster claws). When not discussing lobsters, chelation refers to the process by which a molecule clutches an ion in a pincer-like grasp. In the case of humic acid, the humic acid molecule holds (or chelates) nutrients and other compounds as it moves through the soil.

Humic acid holds a negative charge, and it chelates positively charged elements, called “cations” (pronounced cat-ions). Plant roots are also negatively charged, and they have a stronger negative charge than humic acid. When added to soil, humic acid bonds to, or chelates, cation elements in the soil like zinc, copper, iron, and manganese. Humic acid has been shown to chelate up to 60 nutrients vital to plant health. It holds these elements until it reaches plant roots. Since the plants have a stronger negative charge than humic acid, they attract the positively-charged cations. The beneficial cations are absorbed into the plant roots, often with the help of mycorrhizae fungi. Humic acid’s unique ability to chelate cations allows otherwise inaccessible nutrients to be transported through the soil efficiently with minimal leaching.

Tomato plants inoculated with root rot at different humic acid application rates. Image courtesy of Science in Hydroponics.

Humic acid also chelates to toxins in the soil, making it healthier and safer. Years of exposure to pollution and pesticides degrades soil quality over time. Residual heavy metals and pesticides can inhibit plant growth. Humic acid locks these elements into its grasp and essentially makes them unavailable to plants, sequestering them within the molecule. This absorption technique prevents plant roots from consuming toxins in the soil.

Another important function of humic acid is its role in fostering a healthy soil ecosystem. It is known that soil that is alive with microbiomes is healthier and more fertile. Humic acid offers a significant source of carbon for the microbiome to feed on. Soils with high humic acid content have a more diverse and active ecosystem. Living soils foster healthy plants, and humic acid plays an important role in stimulating biodiversity.

Lastly, humic acid improves soil structure and fertility. Humic acid is a relatively large molecule, and it creates space within the soil structure. This allows microorganisms to move more freely within the soil, which in turn makes nutrients more readily available to plants. In addition to improving soil structure, humic acid adds stable carbon to soils, improving water drainage and retention. It aerates dense clay soils, and adds organic material to help with water absorption to sandy soils. Humic acid’s unique ability to bond to different elements also helps to make soil more fertile and more efficient. When fertilizer is applied, humic acid can bond to the nutrients in the fertilizer to make them more available to plants.

Give your plants the best chance possible with an EarthMix® garden soil mix that contains beneficial humic acid. Your plants and your soil will thank you.

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