The inner bark of the slippery elm tree, Ulmus rubra, has been valued for centuries for its unique properties. This species, native to eastern North America, produces a reddish-brown inner bark that becomes mucilaginous, or slimy, when moistened. The demand for this material has led to destructive harvesting practices. This guide outlines the proper, ethical, and sustainable methods required for collecting slippery elm bark while preserving the health of the tree and the species’ population.
Identification and Conservation Status
Positive identification of Ulmus rubra is paramount before any harvesting begins. The leaves are quite large—typically four to eight inches long—with an asymmetrical base and a distinctly rough, sandpaper-like texture. The outer bark of a mature tree is generally gray with narrow, flat ridges and shallow furrows. The definitive test involves nicking a small piece of the bark to reveal the reddish-brown inner layer, which becomes immediately slippery to the touch because of its high mucilage content.
While the species is widespread across the eastern United States, the conservation status of slippery elm is a serious concern. The tree is highly susceptible to Dutch Elm Disease, a devastating fungal pathogen. Historical commercial harvesting often involved felling the entire tree to strip the bark, a practice that is inherently unsustainable. Because of these threats, the United Plant Savers lists slippery elm as an “at-risk” species. Always secure explicit permission from landowners and confirm that local laws permit harvesting before approaching any tree.
Preparation and Timing for Harvest
Selecting the correct time of year directly impacts both the quality of the bark and the ease of its removal. The optimal period for harvesting is generally late spring to early summer, typically between late March and early June. During this time, the tree’s sap is flowing vigorously, which causes the inner bark to swell and separate easily from the outer bark and the wood. This fluid-filled state makes separating the desired inner bark layer more efficient.
Gathering the appropriate tools ensures a clean and precise harvest. You will need a sharp, sterilized knife, such as a utility or grafting knife, and a clean bucket or bag for collection. Harvest should be limited only to small, non-essential branches, or from trees that have already been felled for other purposes. Never remove bark from the main trunk of a living tree, as this will cause it to become “girdled” and die by cutting off its nutrient flow.
Step-by-Step Harvesting Technique
The sustainable technique focuses on removing the bark from a small branch without compromising the rest of the tree. Begin by selecting a branch roughly one to two inches in diameter and ensuring it is free of any visible disease or pests. Using a sharp knife, first clean the surface of the branch by gently scraping away any moss or lichen to prevent contamination of the inner bark.
Next, score the bark by making a shallow cut through the entire thickness of the bark layer. Make a vertical cut along the branch, then make horizontal cuts at the top and bottom of the desired section to create a manageable rectangle. It is critical that these cuts only penetrate the bark and do not nick the underlying wood. Damage to the sapwood hinders the branch’s ability to transport water and nutrients.
The next step is “rossing,” or separating the inner bark from the outer, corky layer. Carefully peel away the coarse outer bark until the smooth, reddish-brown inner bark (the cambium layer) is exposed. This inner layer is the desired medicinal material and should be carefully scraped or peeled away using the sharp edge of a knife. To ensure the branch’s survival, remove only a thin vertical strip of inner bark, leaving a wide strip intact to allow for continued growth and healing.
Post-Harvest Processing and Storage
Once the inner bark has been harvested, it must be processed promptly to maintain its quality and prevent degradation. If the bark has been collected in larger strips, it should be cut into smaller, narrower pieces to facilitate thorough drying. This step is important because the high moisture and mucilage content can encourage mold growth if not dried quickly and efficiently.
The cleaned strips should be laid flat and separated on a screen or rack in a well-ventilated area. It is important to avoid direct sunlight, which can degrade the bark’s potency and color. Turn the strips daily to ensure even air exposure on all sides. This process typically takes less than a week to complete.
The bark is fully dry when it is brittle and snaps easily when bent. Once completely dry, it should be stored in an airtight container to protect it from moisture and pests. Keep the container in a cool, dark, and dry location to maximize the retention of its beneficial compounds until it is ready for use.