Slippery elm is a type of tree that is native to the United States. It is large--frequently reaching over 80 feet in height--and commonly grows along riverbanks, bottom land and other areas where the soil is moist. Slippery elm is well known for its inner bark, which has been used as a medicinal herb for centuries.
The slippery elm is a deciduous tree that grows from southwest Maine to northwest Florida and west to central Texas, Oklahoma, the Dakotas, Michigan, and Minnesota. It is moderately fast-growing and can live for over 200 years. The leaves are oval with a pointed tip and serrated edges. The outer bark is reddish-brown with deep furrows. The inner bark is greenish in color and very slippery to the touch, from which the name of the tree is derived.
The inner bark is slippery because it contains large quantities of mucilage. Mucilage is a clear, thin, sticky liquid that used by the plant to store food. Mucilage is so sticky, that it is often used as a form of glue. Many other plants produce mucilage, including marshmallow plants, from which marshmallow candy once made. Mucilage also acts as a demulcent, a material that acts to soothe mucous membranes.
Native Americans first recognized the medicinal properties of slippery elm, using the inner bark to make a tea or powder that served as a laxative and eased childbirth. They also crushed the bark and used it as a dressing for toothaches and wounds. The same treatment was applied to gunshot wounds by surgeons during the American Revolution. A gruel of the nutritious inner bark was also used. Early Americans also used slippery elm extract to prepare salves for skin ailments and burns.
Today, slippery elm is still used as a medicinal herb in a variety of preparations. The U.S. food and Drug Administration has declared the plant as safe and has approved its use as a demulcent. Lozenges are made with slippery elm to ease the pain of a sore throat and as a treatment for colds. The powdered bark is also sold as capsules, tablets and loose in coarse or fine forms for incorporation into herbal remedies. The bark is also incorporated into commercially available herbal teas.
The inner bark of the slippery elm is harvested in spring or fall by removing the coarse outer bark then stripping the inner bark from the branches. In many instances, the entire tree is stripped, killing it in the process. This is both unnecessary and unfortunate, as it takes up to 10 years of growth before a slippery elm tree is ready for harvesting. If only 1/4 of the branches are harvested, particularly from pruned limbs, the tree will survive and remain a viable and sustainable resource.