How to test soil PH level Vinegar: Take a sample of dry dirt (about 1/4 cup), mix with distilled water to make a liquid “mud” and then start pouring household vinegar over top. If the mixture fizzes, it’s alkaline. Baking soda: Mix dry dirt and distilled water as above then start sprinkling baking soda over top. If the mixture bubbles, it’s acidic. If neither test produces a reaction, you have fairly neutral soil.