Crush the fennel. Put peppermint, ginger, and fennel (or chamomile) in the glass jar.
Fill the rest of the jar with alcohol and water. If you don't have enough liquid to cover your herbs fully, add a little more alcohol and water in a 2:1 ratio until you do.
Cap the jar and keep in a cool dark place for at least two weeks, but up to six. Shake occasionally.
After 2-6 weeks, strain the herbs out with a fine mesh strainer or cheesecloth. Compost the herbs.
Store your tincture in glass dropper bottles in a cool, dark place.