Gather fresh or dried rosemary, a carrier oil, a clean glass jar, and a strainer or cheesecloth
Fill the jar with rosemary
Pour carrier oil over the rosemary until fully covered
Seal the jar tightly
Place the jar in a warm, dark spot for 2 to 6 weeks
Shake the jar gently every few days
Strain out the rosemary
Transfer the oil to a clean bottle
Apply a small amount to the scalp and hair
Store the oil in a cool, dark place