#2 Vinegar
If there is one organic thing that has been known to be an effective weed killer, it is acetic acid. And the easiest thing to get with a high concentration of acetic acid is white vinegar. It contains around 5%, and while it is very useful to clean with it around the house, it can also be a good way to get rid of pesky weeds.
While the concentration is not enough to effectively kill all the big roots, it can be a great way to burn the tops off without having to use any heat. And, if you are persistent and keep applying it, you can get amazing results. Just make sure you are careful not to kill other nearby plants you want to keep as well.