To kill weeds naturally, you can use either boiling water poured directly onto the weeds or a mixture of white vinegar, salt, and dish detergent, which then can be sprayed on them.
To make the solution, you will need one quart of white vinegar, 1/4 cup of salt, and two tablespoons of dish detergent. Mix everything together until the salt dissolves. Put the solution in a spray bottle and spray directly on the weeds that you want to kill, making sure it gets to the roots. When using the spray, it is recommended to make sure there is no rain in the forecast. This way the solution can really work and kill the weeds without it being diluted by the rain. Make sure not to skimp on the salt either; salt will dehydrate the roots and leave the soil a hostile environment of any weeds that are planning on growing there in the future.
Boiling water and carefully pouring them on the weeds is a great method to use as well when killing weeds that are growing in the cracks of your sidewalks. Boiling water literally burns and destroys the root systems of the weeds, causing them to die. Boiling water will kill whatever plant it gets on so be sure to be careful when using this method.