Rosemary oil is a popular ingredient in hair-care routines, and many people combine it with other oils to condition their hair and care for their scalp. If you are wondering whether you can mix rosemary oil with coconut oil, castor oil, argan oil, or other hair oils, the answer is yes, provided you use the right type of oil and follow proper dilution guidelines. It is also important to distinguish between rosemary essential oil and rosemary-infused hair oil.