Homemade Weed Killer 1 gallon of white vinegar, 1/2 cup salt, Liquid dish soap (any brand), Empty spray bottle. Put salt in the empty spray bottle and fill it the rest of the way up with white vinegar. Add a squirt of liquid dish soap. This solution works best if you use it on a hot day. Spray it on the weeds in the morning, and as it heats up it will do its work. Good to know!