You have to use it when it's not expected to rain for 36 hrs or so. Spray in the morning after the dew has evaporated. 1 qt white vinegar and c epsom salts, dish soap, mixed in water, in a sprayer bottle
Weed-Be-Gone Recipe: 1 gallon of vinegar, 2 cups epson salts, cup dish soap. I prefer this recipe over the conventional alternative because it is all-natural and doesn't contain insecticides that would kill pollinators that I am trying to attract.
Acquiring and Purifying Water | Urban Survival Skills That Could Save Your Life