A golf course superintendent feeds the deep color on a putting green with a fertilizer made from dried, heat-treated Milwaukee sewage, on purpose. Here’s the golf course maintenance reason.
The product is Milorganite, and it sits on a pallet in the maintenance building of thousands of American golf courses. It starts as the biological sludge left over when Milwaukee cleans its wastewater with the activated sludge process, a method the city tested in 1915, formally adopted at the end of 1919, and built out at the Jones Island plant from 1923, the largest operation of its kind in the world when it opened. Cleaning the water left a mountain of dried sludge, roughly six percent nitrogen and about two and a half percent iron, built entirely from the bodies of the microbes that ate the sewage. Those are fertilizer numbers.
The superintendent reaches for it because of what that nitrogen does. Synthetic urea greens turf in days, but it hits as a surge that throws a flush of growth to mow off and can scar a green if a storm concentrates it. The nitrogen in Milorganite is locked inside dried microbial cells and releases slowly, over weeks, at a rate soil temperature controls, so there is almost no way to burn turf with it. The heavy iron load darkens the green without pushing growth, which is the exact color you see, and because it is carbon-based organic matter it feeds the soil biology too, not just the plant. The tradeoff is weight, you spread far more product for the same pounds of nitrogen, so it is the slow base feed under a program, never an emergency fix.