The effect of fertilizer on water pH

A hidden benefit of many fertilizers is their ability to lower the pH of the water. Had I kept this in mind this past spring, my trees would be a lot greener today.

Looking back on my fertilizing habits, I shouldn’t have been surprised that my pines remained yellow despite repeated fertilizer applications. I changed my fertilizer protocol this year – as I do most years – but this change was bigger than most as I switched from a mix of liquid and dry fertilizers to mostly liquid fertilizers.

Although I’ve used domestic products like Dr. Earth Life pellets and E.B. Stone organics, as well as Japanese fertilizers including Omakase pellets and Biogold, my primary dry fertilizer has been cottonseed meal.

Applying cottonseed meal to the surface of the soil

When I’ve supplemented cottonseed meal with liquid fertilizer, my go-to has been fish emulsion.

Applying fish emulsion

It turns out both cottonseed meal and fish emulsion have an acidifying effect on the water. When I mixed two tablespoons of cottonseed meal to two cups of water, the pH went from 9.0 to 7.5.

The change was even more dramatic with fish emulsion. When I added several tablespoons to a gallon of water, the pH registered 4.4.

Toward the end of last year, I decided to forego using cottonseed meal in tea bags as various critters – rats, squirrels, raccoons – were treating the teabags as to-go bags and running off with the fertilizer. Rather than fight this, I decided to use more liquid fertilizer going forward.

I started using Dyna-Gro Grow with a Dosatron this spring, and I was happy when I found that the water/fertilizer combo had a pH of 6.2-6.5 depending on the concentration I used.

A pH reading smaller than 7.0 – a success of sorts

I’ve been alternating Grow with fish emulsion and been happy with the results. It’s only recently that I’ve reflected on the fact that on days when I’m not fertilizing that the pH has been above 9 without cottonseed meal to help keep the pH in check. In other words, this is the first time in a long time when I’ve applied high-pH water to my trees with nothing to acidify it before it reached the roots.

I now feel like I have a fuller picture of why my trees were yellow this year. Fortunately, the solution in this case is pretty straightforward – I can start acidifying the water on days I don’t fertilize. More on that in the next post.