It is understandable that, even if you aren't an active environmental supporter, you would not want to use harsh chemicals on your lawn. These chemicals can seep back into well water. Many can also be absorbed through the skin and harm children and pets that play on your lawn. Commercial weed killers are typically systemic in nature; they interrupt some vital part of the weed's life cycle. There are no ecologically friendly systemic weed killers, but that does not mean you can't improvise.
A simple recipe for getting rid of weeds is to take a large pot, filling it with 1 gallon or water, mixing in 1 cup of salt, and then bringing it to a boil. While it's boiling, the pour the solution over weeds. The heat scalds the exterior of the plant to the degree that it is unable to retain moisture and is vulnerable to infection. This results in the death of the plant and the salt helps ensure that any seeds from the weed do not germinate.
Boil 2 pints of vinegar for five minutes. Allow to cool and then add 2 tbsp. of lemon or lime juice. Mix with 1 tbsp. of dish soap and either pour directly onto the weed or use in a spray bottle. Acetic acid is a weak organic acid.
Household vinegar is about 5 percent acetic acid. By boiling away some of the water content in vinegar, you can increase the acetic acid volume up to 10 to 15 percent. The lemon juice helps increase the acidity of the solution as well, while the dish soap increases the mixture's viscosity so it more effectively coats the weed.
While the acid can burn and damage a weed's leaves, the intent is for it to reach the roots, where the acid changes the chemistry of the weed's sap and root cells. This plant can no longer absorb water or nutrients and dies shortly after. This happens to lawn grass and wanted plants as well, so be careful to apply it only on weeds.
Take plain coconut oil and spray it over the weed's leaves. The oil's normal viscosity is enough to hold it onto the leaves with no further assistance. Coconut oil contains a small percentage of a fatty acid known as pelargonic acid or nonanoic acid. It reacts with the waxy outer membrane found in all plant leaves and dissolves it. By doing this, the weed is unable to retain moisture and will shrivel within the day.