Why Some Iron Products Work and Others Not

Q. I see you mention a specific iron product every year, but I decided to buy it for use early next spring. We prefer to buy it online. When I searched for it, about 80 choices appeared and now I am confused.

A. Not many places stock this iron fertilizer locally. Helena Chemical and Viragrow are the only places I know locally that carry it locally. 

            I have been waiting for an excuse to explain this iron dilemma more thoroughly. Using the wrong iron product when the chemistry of the soil or water is not right, results in a waste of time and money.

            The chemistry of our desert soils is responsible for most yellowing seen in plant leaves. You are right, there is a huge variety of iron products available. Which one to use? The problem is not with the product. The problem is matching the product to our soils because of their chemistry.       

            There are two methods for applying iron to yellow plants; a single application to the soil in early spring or 3 – 4 applications of an iron spray directed toward yellowing leaves later in the season.

            A single iron fertilizer application to the soil makes green leaves continuously as the plant grows through the year. Multiple sprays of iron to the leaves is the only method that corrects leaves already yellow. Each spray, a few days to a week apart, makes the leaves darker and darker.

            All iron fertilizers work IF the soil pH (which is related to its alkalinity) is 7.5 or lower. If an iron product is applied to the soil and expected to work, the soil pH must be 7.5 or lower. If an iron product is mixed with water and sprayed on the leaves, the pH of the water must be 7.5 or lower. The magic number to remember is 7.5. Most desert soils and our water supplies are closer to 8. This becomes a problem for all iron products except one.

EDDHA iron products at Viragrow. 1 pound container top
and 5 pound package on bottom.

            Iron fertilizers that contain the chelate EDDHA are 100% effective with any amount of alkalinity. That’s right, any amount. But the chelate in the ingredients MUST be EDDHA.

            When applying iron fertilizer to soils in early spring, just before new growth appears, use an iron fertilizer containing the chelate EDDHA. It will tell you so in the ingredients.

            Later in the growing season when leaves begin yellowing, all iron fertilizers sprayed on the leaves work IF the pH of the water is below 7.5. Use distilled water or water from reverse osmosis. This water has little alkalinity and a pH of 7.

            It’s difficult to get iron sprays inside the leaves. Leaves have no roots, so we must improve the movement of this iron spray inside the leaf. This is done by “making the water wetter”. Adding a liquid detergent to the spray at the very end of mixing helps movement of the iron inside the leaf.