Walk down the lawn and garden aisle of any major home improvement store or independent nursery in Austin, Seattle, or Los Angeles, and you will find jugs of horticultural vinegar proudly displayed on the shelves. Sold as a natural, eco-friendly alternative to synthetic herbicides, this liquid has exploded in popularity among homeowners looking to transition away from glyphosate-based weed killers.

Yet, turn the jug around, and you will be greeted by severe, high-contrast hazard warnings. The labels feature explicit commands: “DANGER: CAUSES IRREVERSIBLE EYE DAMAGE,” “CORROSIVE,” and “KEEP OUT OF REACH OF CHILDREN.”

Discovering vibrant green, carpet-like moss climbing up an interior wall can be shocking for any property owner. Whether it is a damp basement wall in a historic New York brownstone, a moisture-prone laundry room in a rainy Seattle suburb, an indoor atrium in a San Francisco flat, or a humid sunroom in Austin, Texas, moss indoors is an urgent signal of an environmental failure.

In a race to eliminate the growth quickly and without synthetic bleaches, many property owners reach for industrial vinegar (also known as horticultural vinegar). Because it is a powerful, plant-killing natural herbicide, it seems like the perfect solution to spray directly onto the moss.