Removing Fertilizer Stains on Concrete

By Chris Sullivan – ChemSystems, Inc.

Question:

I have a concrete patio and used a plant food called Bloom Booster when watering the planters on the patio. The next day, I noticed everywhere water ran out of the planters, it stained the concrete. I have tried scrubbing with a brush attached to a power-scrub setting on my hose. What can I do?

Answer:

Plant food and fertilizers all contain metals and minerals such as magnesium, iron, copper and zinc. This list of ingredients reads very much like that of concrete acid stain. In essence, you stained your concrete with plant food. The minerals have penetrated the concrete and reacted with the cement to form a permanent color change. The reacted minerals are not water-soluble, which means water and scrubbing will not remove them. They are only soluble in a mild acid solution.

I would start with a clear white vinegar, diluted 50:50 with water, and see if that brings the stains out. You will need to apply the acid solution on the stain multiple times, scrub lightly, and then rinse. Test in a small area to ensure you are getting the results you desire. If the vinegar does not work, you may need to try a stronger acid, such as muriatic. Dilute the stronger acid 40:1 with water. Also, be aware that the acid may etch or change the profile of the concrete in the areas you clean.

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