Comfrey is a perennial herb that produces deep roots, large leaves and pinkish flowers. Many home gardeners grow this herb for medicinal purposes. Although arguments exist concerning the medicinal value of comfrey plants, many herbalists extract the oil for use in various treatments. Essential oils are small portions of plant material comprised of chemical compounds. Separating the comfrey oil from the rest of the plant provides the ingredient for many herbal preparations.
Harvest your comfrey leaves before the plant begins flowering. When allowed to flower, these blossoms pull nutrients from other parts of the plant. Begin harvesting a few months after planting your comfrey plants. Trim off sections of the leaves with sharp scissors. Cut selected leaves off from the rest of the plant about 5 cm above the ground. Avoid injuring the crown and immature shoots during cutting. Harvest leaves up to four times a year on mature, healthy plants.
Rinse your comfrey leaves under a stream of cool water. Pat the leaves dry with a clean cloth or a paper towel. Remove any damaged or diseased leaves. Toss out any weeds. Set the comfrey leaves on clean newspaper or paper towels to dry for a few days. Place the leaves in a sunny spot to encourage rapid drying.
Wash your hands before handling the dried leaves. Crush the dried leaves between your fingers or use an herb mortar and pestle. Measure about 4 ounces of the dried leaves into a jar. Add 1 pint of vinegar or alcohol to the leaves. Do not use rubbing alcohol in herbal preparations intended for ingestion. Vinegar or vodka make suitable ingredients for extracting essential oils intended for ingestion. Gently shake the jar once or twice each day. Allow the comfrey to steep in the jar for at least four days.
Separate the liquid from the solid particles by slowly squeezing the mixture through a clean piece of cheesecloth. This liquid contains the essential oil. Like many purchased oils, the essential oil combines with the extraction liquid, such as vinegar or alcohol. Divide the liquid into individual containers. Tightly seal with lids until ready for use.