I am often asked, “What is better for plants, humic acid or fulvic acid?” The simple answer is: “It’s better to use humic acid at the roots and fulvic acid as a foliar spray.”
Humic acid is actually a combination of humic and fulvic acids. The humic acid fraction consists of larger molecules with lots of positive and negative charges on the surface of the molecules. It isn’t actually taken up through the roots, but it lightly holds onto mineral salts in the root zone, making them much more available to the plant. It is especially helpful in soils with high clay content. Clay particles have a strong negative charge, and they tend to hold onto positively-charged minerals too tightly. So the clay can lock up some important plant nutrients such as potassium, calcium, magnesium and essential trace elements. Humic acid forms a bridge between the clay particles and the mineral cations, holding them loosely enough to be taken up easily by the roots.
The fulvic acid fraction has a much smaller molecular weight, and it is more biologically active. In fact, fulvic acid not only attaches to minerals, it can actually transport them through the cell membrane and release them inside the cell! So fulvic acid makes a great foliar spray, allowing trace elements such as copper, iron, manganese and zinc to be better absorbed through the leaves. After releasing the trace elements, the fulvic acid can be metabolized and used by the plant to build carbon skeletons.
In hydroponics, either humic or fulvic acid would work well, but if you wanted me to split hairs, I would look at your water source first. If you use a “soft water” source such as RO water, I’d lean towards humic acid. Since it has lots of positive and negative charges, it should help stabilize pH. Remember, RO water has practically no buffer for pH. The pH can spike upwards during rapid vegetative growth, and it can crash during heavy fruiting and flowering. Humic acid can help neutralize both acid and alkaline conditions, with a nice moderating effect on your plants.
If you use “hard water”, I would probably shift the balance towards fulvic acid. Hard water is usually high in calcium and magnesium, and the fulvic acid will help keep the positively charged calcium ions more soluble and available to the plant. The humic acid fraction is heavier, and may cause the calcium to precipitate out of solution. But don’t forget, humic acid has fulvic acid in it, too! So when you use humic acid, you are also adding a little fulvic acid.
In the lab, I love to play with the balance of humic acid to fulvic acid, tweaking them in for the best effects! So why don’t you keep both humic acid and fulvic acid powders on the shelf? You can mix one for the roots and the other for the leaves. Or better yet, combine the two in a custom formula. Before long, you will find the perfect mix for your perfect plants!
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