How much salt can kill a red headed irishman cactus?

Red-headed Irishman cacti, like most cacti, are sensitive to salt and can suffer damage even at low concentrations. While there isn't a specific lethal dose, exposure to high levels of salt—typically above 1,000 ppm in soil—can lead to stress and death over time. It's best to keep these cacti in low-salt environments to ensure their health and longevity.