Natural Ways to Eliminate Carpetgrass from St. Augustine Lawns

Know Your Enemy

Carpetgrass (Axonopus affinis) thrives in low pH (5.0–6.0), low fertility, and constant moisture. It cannot tolerate salt or alkaline conditions. St. Augustinegrass, conversely, prefers pH ~7.5 and handles moderate drought.

Why Herbicides Are a Dead End

MSMA (arsenic-based) and Asulam (carbamate) were banned for cancer risk and water contamination. Searching for black-market alternatives is dangerous and illegal.

Cultural Controls That Work

1. Raise pH with lime. Calcareous Florida soils are naturally alkaline—carpetgrass hates it. A lime application pushes pH toward 7.5, stressing carpetgrass while benefiting St. Augustine.
2. Boost potassium. Strengthens St. Augustine roots, improves drought tolerance. Dry the soil intentionally (cover with plastic if raining) to exploit carpetgrass's moisture dependence.
3. Amend with organic matter. Humus, peat, compost invigorate St. Augustine; carpetgrass declines in rich, well-structured soil.
4. Shade the patches. Black plastic over weakened carpetgrass blocks light and accelerates death.

The Philosophy

Don't fight weeds with poisons—change the environment so your desired grass outcompetes them. Safer, cheaper, and permanent.