Muriatic acid is a harsh chemical, sometimes referred to as hydrochloric acid. Pool supply stores sell the product because it's designed to stabilise the pH balance in swimming pools. Even when used around the house, you mix the acid water first, which dilutes the harshness of the chemical. Muriatic acid burns through nearly anything it touches, making it a suitable killer for weeds and adult trees around your home. It's best to use muriatic acid with caution, as it can kill other plants in the surrounding areas.
Combine the muriatic acid with water in a metal bucket, according to the manufacturer-recommended ratio on the back of the bottle. Wear rubber gloves and goggles to protect your hands and eyes from the acid, as it's extremely harsh and dangerous.
Dig around the base of the adult tree, making a trench deep enough to expose the roots.
Pour the muriatic acid directly onto the roots of the tree.
Cut the tree down to just a stump, removing the upper branches and portions of the tree. Pour more of the acid mixture on the top of the stump, forcing the tree to absorb the acid in multiple ways.
It typically takes several treatments before an adult tree completely dies. Add more of the acid mixture to the roots and stump of the tree every few days.