Humic and fulvic acids are two of the hardest working and most versatile amendments you can give your crops. They are both naturally formed by the microbial action and degradation of carbon-based materials in soils. All healthy soils have some amount of these important acids which are most commonly found in the layer of organic material or humus. Their importance to soil fertility, root growth, nutrient uptake, and increased yield has been known and studied for almost 200 years, though most useful results for the home grower have emerged in the last few decades.

Humic Acids*

Humic acids (HA), the primary humic substance, are a hydrophobic compound. They are soluble in high pH environments (alkaline), but stable in neutral and acidic environments. In nature they are found in all soil types. In clay soils, they help to break up compacted soil masses; in sandy soils, they help to retain moisture by decreasing the rate of evaporation. The structure of HA varies greatly depending on where they are found. In various forms, they can assist in increasing the rates of seed germination, help to increase and even kick start the development of microbial and microfloral communities in soils.

*All of these results (and many more) can be found in the fall 2015 issue of Scientiae Horticulturae by authors L.P. Canellas, et al.


Fulvic Acids

One of the key differences between the two acids is fulvic acids (FA) are soluble at all pH levels, not just alkaline conditions. This means they are essentially useful and useable to plants regardless of soil condition or media type. Other important distinctions include FA’s double oxygen content and exchange capacity as compared to humic acids.

Compared to clusters of HA, fulvic clusters are significantly smaller. This allows for ready entry into stomata and openings in the stems, branches, shoots, and roots of plants. This is an important trait of FA as they are able to collect minerals and elements on the plant surface and carry them into plant tissue and cells. This is especially true when FA are applied as part of a foliar application.

Read more: Fulvic Acid: A Golden Opportunity

Combined Benefits of HA and FA

Both HA and FA can be found in many commercially available fertilizers and amendments. They can be thought of as “helpers” as they enhance a plant’s ability to effectively utilize nutrients and trace elements. Studies have shown the delivery of the macronutrients nitrogen, phosphorus, and potassium is often at least 100 per cent, and as much as 500 per cent more effective when coupled with an appropriate amount of HA or FA. Humic and fulvic acids are also widely used to increase the health and size of roots, shoots, stems, leaves, and fruits of most crop types. Additionally, they are known or thought to:

  1. Aid in the transport of various nutrients by moving minerals throughout cell membranes.
  2. Accelerate plant metabolism. Effects have been noted as soon as eight hours after application.
  3. Increased carbohydrate production. This is evident starting between 24 to 48 hours after application and can be directly attributed to higher quality and increased yields.
  4. Enhance the chlorophyll content of plant leaves. This corresponds with an increase in the uptake of oxygen in the plant.
  5. Help regulate plant growth hormones.

When and How to Apply Humic and Fulvic Acids

Plants at any stage of development can benefit from appropriate dosing of HA or FA. Younger plants and seedlings tend to reap a higher benefit from humic substances, but any actively growing plant or plant tissue will favorably respond to either HA or FA.

Younger plants and younger foliage on older plants which are more actively metabolizing make more efficient use of humic substances. In any instance, they are not needed in large quantities to be beneficial.

In concentrated forms, not much HA is needed to be effective. No more than 0.01-0.02 ounces per gallon is needed (about 100 mg per liter of water). Too much HA can inhibit or slow down root, shoot, branch, and leaf growth. This is primarily relevant for foliar applications. When applications of humic substances are made to the soil, the concentration can be higher as a substantial amount will remain in the soil and only one quarter to one third may be absorbed and translocated throughout the plant. Foliar applications can be best utilized if mixed with other trace minerals needed and timed to correspond with the needs of the plant in its respective stage of development. These would correspond for the most part with the onset of vegetative growth, development of flowers, setting of seeds or fruits, and subsequent ripening.

Read also: The Do's and Don'ts of Foliar Feeding

Results of HAs and FAs on Various Crops

Countless studies have been done to evaluate the benefits of numerous types of humates and humic substances in various doses on hundreds of different crops. Individual results can be found throughout scientific journals, but as examples of the effectiveness of humic and fulvic acids, check out just a few published results*:

Fruits and…

  1. Apricots sprayed with various doses of commercially available HA showed increased yields between 16 and 33 per cent based on dosage.
  2. Peaches given foliar applications and/or soil applications of commercially available HA showed increased fruit yields up to 80 per cent.
  3. Hydroponically grown strawberries given HA showed yield increases up to 33 per cent as well as improved fruit firmness.
  4. Passion fruit sprayed with varying doses of HA at various times during development displayed a 124 per cent increase in dry root mass, suggesting that the HA caused significant increases in root development.

Vegetables and…

  1. Seeds of beans were treated with HA; higher germination rates, faster growth and higher yields were all noted.
  2. Cucumbers given FA showed increased growth, higher nutrient uptake, and increased flowering.
  3. Tomatoes treated with both HA and FA showed increased dry mass weight, increased fruit yield and decreases rates of Phytophthora.

Allium and…

  1. Garlic sprayed with humic acid showed a two to six per cent increase in size and a longer storage life
  2. Onions sprayed with a blend of humic acid increased yield by five to six per cent as well as an increased marketability (uniform size and appearance) of 26 per cent.

Flowers and…

  1. Chrysanthemums given various doses of HA responded proportionately with increased stem and root dry weights. Flower diameters were increased up to 33 per cent with HA treatments
  2. Gladiola corms were soaked in humic acid for 24 hours prior to planting; increased growth and early flower maturity corresponded.

*From the fall 2015 issue of Scientiae Horticulturae by authors L.P. Canellas, et al.


There can be little doubt that humic and fulvic acids can provide increased yields in a wide range of crops. Like any substance, of course, follow on-label dosing instructions and perform an analysis of your growing media before using any amendment liberally.