Salt. Bring 500 ml of water and 250 ml of salt to a boil, then pour the solution directly onto the plants. Alternatively, sprinkle salt on the soil and then spray with water.
Vinegar. This is lethal for some types of plants: spray vinegar directly on the weed; it will disappear after a few days.
Boiling water. This is a quick and easy remedy: pour boiling water directly on the plant to kill it.
