Cacti can be killed by physically removing them or by using chemicals. Physically removing a cactus can be dangerous, as its spines can easily go through clothes and sometimes even shoes. Herbicides can also be dangerous, as they can affect other plants nearby or even the soil itself.
Cacti are tenacious plants and often regrow. If using a physical method, take out as much of the cactus as possible, using a shovel to remove its root system. If using a herbicide, make sure to keep the chemical at least 20 yards from desirable plants and trees and at least 100 feet from water sources. The best time of the year to eradicate a cactus is at the start of the growing season and when the temperature does not exceed 90 degrees.