Humus, Humic acid and Fulvic acid: Different Uses for Plants

Are you wondering about the differences between humus, humic acid and fulvic acid?

In this article, we will explain their differences in uses for plants and how to apply them in your garden.

1. Appearance

Compost and humus have a similar appearance both being dark brown with a soil-like texture. Humic acid is also dark brown but in powder, granular and liquid forms. Fulvic acid has the most distinct appearance, as powder or liquid which is golden brown in color.

Compost

Compost is an organic matter made from plant biomass like leaves, twigs, fruit peels, grass clippings, wood chips, etc.

It has a dark brown color and soil-like texture, and the constituents are no longer identifiable.

Humus

Humus and compost are related materials and are often confused with each other. They have the same soil-like texture and dark brown appearance.

The main difference between the two is that humus is completely decomposed organic matter that resists further decay, while compost, despite its soil-like appearance, is just partly decomposed.

In essence, compost is a step away from humus, and compost will eventually become humus.

Humic acid

Humic acid can be extracted from soil humus, peat humus, and leonardite (soft coal).

Humic acid is the same dark brown color as the materials it’s extracted from.

It is made of stable molecules that are highly resistant to decomposition and are soluble only in an alkaline environment.

Commercial products of humic acid are available in liquid and granular forms.

Fulvic acid

Just like humic acid, fulvic acid can be extracted from peat humus, and leonardite, and is also resistant to decomposition.

Fulvic acid products are also available in powder and liquid forms.   

But unlike humic acid, fulvic acid has a light brown to golden brown color and is soluble in water at all pH levels.

2. Are they plant fertilizer?

Humic acid, fulvic acid, and humus are all beneficial to plants in improving the plant’s water and nutrient uptake, enhancing its growth and yield.  But only humus is a fertilizer.

Humus

Humus can improve soil water-holding capacity, improve aeration and supply nutrients that enhance plant growth. And it is also a fertilizer with abundant plant nutrients.

A study found that the use of humus significantly increased the growth of lettuce in the number of leaves, leaf size, plant weight, and concentration of nutrients (Ekbic and Kose, 2022).

Humus is an excellent soil amendment. When mixed with soil, it can greatly increase the water-holding capacity of the soil by making more water available to the plant.

Additionally, humus is a fertilizer as it contains an abundance of plant minerals such as Nitrogen and Potassium from decayed organic matter.  These nutrients are taken up by the plant to enhance growth.

Because of the water-retentive nature of humus, it also attracts soil organisms like insects and earthworms.  The action of these organisms improves soil aeration and drainage, supplying more air to the plant roots, and preventing water logging.

Humic acid

Humic acid can also increase the plant’s water and nutrient intake, and also neutralize soil pH and soil toxicity.  But it is not a fertilizer with plant nutrients.

Research has proven the benefits of humic acid on plants that it can result in a 38 to 62% increase in plant yield (Ayuso et al, 1996).

Humic acid can increase the nutrient capacity of the soil by chelating nutrients in the soil and preventing them from leaching away. 

It is a bio-stimulant.  When used in the soil or as a foliar spray, it increases cell wall permeability so that the plant can absorb more nutrients.

Humic acid can also lower soil pH, neutralizing it or slightly acidifying it, making it suitable for plants that prefer acidic soils. It can also reduce soil toxicity by trapping toxic metals like lead, arsenic, and mercury, preventing them from getting to the plants.

However, humic acid is not a fertilizer as it does not contain nutrients that can be absorbed by the plants.

Fulvic acid

Similar to humic acid, fulvic acid is not a fertilizer, but can increase plant nutrient uptake by binding soil nutrients in the soil and preventing leaching.

The molecules are small enough that they can penetrate the cells of plants to deliver nutrients directly to the plant cells. One study found that fulvic acid greatly reduced the occurrence of tomato blossom end rot, which is caused by calcium deficiency (Suh et al, 2014)

Like humic acid, fulvic can buffer and neutralize soil pH, and reduce soil toxicity. It can also improve plant growth by stimulating root growth and branching, giving the plant access to more nutrients and moisture in the deeper parts of the soil,

If used properly, fulvic acid can improve plant growth and fruit yield. Researchers found that small doses of foliar spray fulvic acid increased plant height and weight as well as fruit size and number (Suh et al, 2014).

3. Which is the best for plants?

Compost, humus, humic acid, and fulvic acid all promote plant growth in different ways. However, humus produces the best results by combining all the actions of the others.

Humus is a soil amendment and fertilizer. It can improve soil properties such as nutrient content, water-holding capacity, texture, and aeration, all of which lead to improved plant growth.

Humic acid and fulvic acid are collectively known as humic substances. They can both improve plant nutrition, and soil water capacity, reduce soil toxicity, neutralize alkaline soils, improve germination of seedlings, and enhance plant resilience to temperature and water stress.

Humus is very similar to compost with most of the same benefits like water retention, aeration, increased soil microbial activity, and nutrient supply. These alone can positively impact plant growth and yield.

Additionally, humus also contains both humic acid and fulvic acid which produce a different set of benefits for plants such as reduced toxicity, enhanced stress, disease resistance, and improved seedling germination. Humus thus combines the individual benefits of compost, humic acid, and fulvic acid, and delivers the best results for plants.

https://www.youtube.com/watch?v=mVZjuaJM6k8

4. Are they necessary in the garden?

Compost and humus contain small amounts of humic and fulvic acids that are beneficial to plant growth. So, if you have compost, you may need to buy humic and fulvic acid products.

Compost, humus, humic acid, and fulvic acid are necessary for the optimum growth of plants, as they help plants in numerous ways. And there are no true substitutes for these substances.

Compost and particularly humus contain small quantities of humic acid and fulvic acid, and the small quantities are generally sufficient for plants. 

Research has shown that higher doses actually do not necessarily improve plant growth (SU, 2022), and in some cases can even impact growth negatively (Gunes et al, 2016).

Thus, rather than purchasing humic and fulvic products, it’s best to invest in increasing the humus content of your garden soil, either by incorporating more organic matter in the form of compost, mulching, or by purchasing humus-rich soils to add to your garden.

5. How to use humus for plants?

Humus can be applied by mixing it with the garden soil or potting mix. It can also be made into a liquid compost tea and used as a soil drench.

The way you apply humus depends on the type of garden and the growing conditions. For houseplants and container plants, mixing in the humus with potting soil before planting is ideal. The humus should make up about one-quarter of the entire potting mix. Some commercial potting mixes contain compost, and in this case, you should use less humus.

For raised beds and gardens, spread 2 inches (5 cm) of humus over the soil and work it into the top 6 inches (15 cm) of the garden soil before planting.

You can also use humus as a mulch for existing plants both in pots and in the garden by incorporating 2 inches (5 cm) of humus around the base of the plant.

Another way to apply humus/compost is to turn it into compost tea (by adding water and brewing for 36 to 48 hours) which can then be used to water the plant and as a foliar spray every 2 weeks.

Can you plant directly in humus?

Humus is an excellent soil amendment, but it is not soil and you can’t grow plants directly in it.

Humus drains easily when not mixed with soil, it’s also too light-weighted and can’t support growing roots, so plants will topple over.

Humus has to be mixed in with soil, or used as a top dressing

6. How to use humic acid for plants?

Humic acid is best applied in liquid form as a foliar spray or soil drench.

Humic acid is available in liquid, powder, and granular forms. The liquid form is the best to use as it doesn’t require any mixing with soil which poses the risk of damaging the roots.

Liquid humic acid should be dissolved in water and used to water the soil around the roots as you would do with plain water.

Powdered humic products can also be dissolved in water and used as a soil drench or foliar spray.

The dosage for diluting and using the humic acid depends on the products as different brands use different concentrations. But generally, you can apply humic acid once every 2 weeks.

Can you plant directly in humic acid?

Despite its many benefits, plants can’t grow directly in humic acid. This is because it cannot support the plant’s roots.

Additionally, humic acid itself is not a fertilizer and has little nutrient content. It has to be mixed in with soil or diluted in a nutrient solution (hydroponics), or else the plant will grow poorly due to malnutrition.

7. How to use fulvic acid for plants?

The best way to apply fulvic acid is as a liquid soil drench and foliar spray. 

Like humic acid, fulvic acid is best applied as a liquid soil drench or spray. Powdered fulvic can also be dissolved in water and used as a liquid product.

Again, the dosage depends on the manufacturer and brand. But it can generally be applied once every two weeks and at the same time as humic acid.

Can you plant directly in fulvic acid?

Like humic acid, you can’t grow plants directly in any form of fulvic acid as it can’t support the plant roots and lacks nutrients. Fulvic acid has to be mixed with soil or a nutrient solution to work effectively.

Happy gardening!

Related

Peat vs Humus: Know the Differences & Uses

Humic Acid vs Biochar: Differences & Uses in Garden

References

Gaffney, J. S., Marley, N. A., & Clark, S. B. (1996). Humic and Fulvic Acids and Organic Colloidal Materials in the Environment. ACS Symposium Series, 2–16. https://doi.org/10.1021/bk-1996-0651.ch001

Fernando Mahler, C., Dal Santo Svierzoski, N., & Augusto Rolim Bernardino, C. (2021). Chemical Characteristics of Humic Substances in Nature. Humic Substance [Working Title]. https://doi.org/10.5772/intechopen.97414

Suh, H. Y., Yoo, K. S., & Suh, S. G. (2014). Effect of foliar application of fulvic acid on plant growth and fruit quality of tomato (Lycopersicon esculentum L.). Horticulture, Environment, and Biotechnology, 55(6), 455–461. https://doi.org/10.1007/s13580-014-0004-y

Ayuso, M., Navarro, P., Hernández, T., García, C. M., & Pascual, J. L. (1996). A Comparative Study of the Effect on Barley Growth of Humic Substances. Extracted from Municipal Wastes and from Traditional Organic Materials. Journal of the Science of Food and Agriculture, 72(4), 493–500.

Gunes, A., Beyzi, E., & Gurbuz, B. (2016). Effects of Humic Acid Treatments of Yield, Morphological Characteristics and Essential Oil Components of Coriander (Coriandrum sativum L.). Research Journal of Soil Biology, 9(1), 1–8. https://doi.org/10.3923/rjsb.2017.1.8

EKBIÇ, E., & KÖSE, M. (2022). Effects of humus and humic acid on plant growth and nutritional uptake of lettuce (Lactuca Sativa L.). Applied Ecology and Environmental Research, 20(3), 2261–2269. https://doi.org/10.15666/aeer/2003_22612269

Su. (2022, April 2). Effects of different doses of fulvic acid fertilizers on tomato yield and quality.