Originally published in The Forest Farmers Handbook: A Beginners Guide to Growing and Marketing At-Risk Forest Herbs by United Plant Savers & Rural Action (available here).
Black cohosh is a perennial species that is commonly found growing along forest edges and in deeply shaded forest interiors throughout eastern North America. Black cohosh plants can grow as a single or multiple stem, each with three compound leaves containing multiple serrated leaflets. Plants are typically tall in stature, with flowering stalks emerging in mid-summer and reaching heights of 3’ to 8’ (Persons and Davis, 2014). Black cohosh rhizomes have long been prized as a valuable medicinal herb and in recent years have become a primary component of commercially available post-menopausal formulations. Between 2000 and 2010, an estimated 2.7 million dried lbs. of black cohosh root were traded on the world market, representing the harvest of approximately 40-54 million plants (Davis and Dressler, 2013). With only 5% of the market demand currently being supplied by cultivated sources (Davis and Dressler, 2013), there is significant need to increase forest-based production of this species.
Black cohosh is typically found growing on north, northeast, and east facing aspects under a mature forest canopy that provides approximately 50%-80% shade. When grown at higher elevations (<3,400 ft.) black cohosh can tolerate as low as 35% shade, which growers report can increase root yields by 18%-20%. Within these baseline conditions, black cohosh prefers sites with well-drained soils that are rich in organic matter, thick leaf litter, and a slightly acidic soil pH (5.5.–6.5) (Davis and Dressler, 2013; Naud et al., 2010). The presence of companion plants and other indicator species can also signify potentially suitable production sites. Species that are commonly found growing in association with black cohosh include, but are not limited to, tulip poplar, sugar maple, basswood, and spicebush (Braly, 2007), Jack-in-the-pulpit, rattlesnake fern, enchanter’s night shade, wild geranium, and other associate species (Burkhart, 2013).
Propagation trials have shown that the growth of black cohosh is highly influenced by soil pH, with the largest increases in root mass achieved at pH levels between 6 and 7 (Naud et al., 2010). This suggests that calcium-based soil amendments and/or liming may be beneficial to black cohosh plantings (Naud et al., 2010). For sites that are less than ideal, such as those with poorer quality soils, inadequate shade, or the lack of companion/indicator plants, modifications can be made to increase your chance for success. Modifications may include developing cultivated planting beds, amending soils to optimize growth, and/or erecting artificial shade structures to provide the proper amount of shade (Davis and Dressler, 2013).
To prepare the growing site for a wild-simulated planting, start by removing any fallen branches, rocks, or other debris that will interfere with the planting process. If necessary, selectively remove small trees and shrubs, or prune low hanging branches to improve airflow and optimize light conditions. If invasive species are present, they should be manually removed and/or controlled prior to planting.
For woods-cultivated plantings, mark the boundaries of your planting beds to prevent damage to surrounding vegetation during the site preparation process. Beds can be made to any size and dimension but should be narrow enough to allow for easy maintenance and management (approx. 4’- 5’ wide). Once the beds have been marked, remove, thin, or prune competitive and suppressive vegetation within the planting area. After the vegetation has been removed, apply any necessary soil amendments, and then shallowly till the beds with a heavy-duty tiller or tractor to loosen the top 3”- 6” of soil.
Propagation trials have shown that black cohosh plants grown under higher light conditions (e.g. 78% shade vs. 90% shade) produce more biomass (e.g. seeds, roots, leaves), and have higher alkaloid concentrations (McCoy et al., 2007; Naud et al., 2010). Regardless of which production method is used, increasing the amount of available light in the growing site may be advantageous.
Propagation from Rhizome Cuttings
Black cohosh is most commonly propagated by subdividing mature rhizomes into smaller rootlets that can be replanted. As illustrated in figure 8, rhizomes should be divided into 1.5” to 3” long segments, each with several fibrous roots and a dormant bud whenever possible (Davis and Dressler, 2013). Fibrous roots facilitate the uptake of water and nutrients, making them critical to the survival of young transplants. Rootlets with healthy fibrous roots present at the time of planting had a 60% higher rate of survival than those without adequate fibrous root material (Small et al., 2011). Differences have also been observed in the growth of transplants based on which part of the rhizome the rootlet originated. After 3 years growth, transplanted rootlets that included the actively growing tip of the root and terminal bud were found to produce higher yields than segments originating from the rhizome midsection (McCoy et al., 2007). Although, when 2-4 buds were present on midsection segments, transplants were shown to produce yields comparable to those reported for terminal segments (McCoy et al., 2007).
If rhizomes and/or rootlets are stored prior to or after subdividing, care should be taken to prevent excess moisture from accumulating in the storage container in order to prevent the growth of fungal pathogens (Thomas et al., 2006; Small et al., 2011). To prevent moisture accumulation roots can be mixed with peat moss and stored in mesh/burlap bags or cardboard boxes that will allow adequate ventilation (Davis and Dressler, 2013).
Propagation from Seed
Black cohosh can also be propagated from seed, but germination can be inconsistent and/or difficult to achieve (Kaur et al., 2013). As with many woodland herbs, black cohosh seeds have an underdeveloped embryo when they ripen on the plant and require a period of warm/cold stratification to break seed dormancy and enable germination to proceed (Persons and Davis, 2014; Kaur et al., 2013). Black cohosh seeds have a relatively weak physiological dormancy, with most seeds being capable of germinating after 8 weeks of cold stratification (Albrecht and McCarthy, 2011). The easiest way to ensure successful stratification is to collect the seeds as they ripen on the plant during the late summer and fall months and sow them immediately after collection. Seeds are ripe and ready to collect when the seed pods turn from green to dark brown, and the seeds rattle inside the capsule when shaken. By sowing immediately, the seeds will be exposed to the natural temperature fluctuations of the seasons and will complete their stratification process without the need for any further interventions (Davis and Dressler, 2013).
Planting Rhizomes and Seeds
Rhizomes and/or rootlets are typically planted in the fall of the year but can also be planted in early spring while the roots are still dormant. Plant roots approximately 18”-24” inches apart in prepared woodland production beds, planting furrows, or individual holes. The roots should be planted deep enough so that the bud is covered by 1”-2” of topsoil and an additional 1”-2” of leaf litter (Greenfield and Davis, 2004, McCoy et al., 2007).
Plant seeds approximately 1.5” deep and 1.5”-2” apart in a prepared woodland nursery bed or wild-simulated planting site and then cover with 1” of hardwood leaf litter (Davis and Dressler, 2013). Seeds that are planted immediately after collection should germinate at a relatively high rate (Albrecht and McCarthy, 2011), but some seeds may not germinate until the following spring (Davis and Dressler, 2013).
Once established, plantings will require periodic maintenance, such as inspecting for signs of herbivory, disease, and mortality as well as pruning or weeding to maintain optimal growing conditions. Because the emerging stalks of black cohosh are strong, they can push through a relatively thick layer of leaf mulch. Periodically applying an additional 4”-6” layer of composted hardwood leaf mulch will help to improve the soil quality and provide for optimal plant growth.
Pests and Disease
Black cohosh is susceptible to infection by several fungal pathogens, including leaf spots, root rots, and damping-off disease (Davis and Dressler, 2013). Diseases are most common in sites with inadequate airflow and poorly drained soils (Thomas et al., 2006), making site selection and preparation an important step in disease prevention. Depending on your location, white-tail deer may also be considered a common “pest” that can cause significant crop damage, particularly by browsing the foliage, which causes reduced root growth and seed production. Growers may also encounter problems with slugs and various species of insects (Davis and Dressler, 2013). As we have previously noted, always use organic insecticides, fungicides, and other deterrents as the first line of defense if serious disease or pest problems arise (Davis and Dressler, 2013).
Using a spade fork or other digging tool, carefully harvest transplanted rhizomes after 4-6 years of growth, taking care to keep all parts of the root intact. Rhizomes should be harvested in the fall when root mass and medicinal potency are at peak levels (Davis and Dressler, 2013).
After harvesting, roots should be washed thoroughly to remove all dirt, debris, and foreign root material. Sometimes breaking the root may be necessary to fully dislodge all unwanted materials. Briefly soak roots in a bucket of water to soften the dried dirt and debris clinging to the root, and then spread the roots on a wire mesh screen and spray with a medium pressure hose. A small soft-bristle brush can also be used to remove dirt from hard to reach areas. Mechanized or hand powered root washers can also be used and may be a better alternative for washing large volumes of root material (Davis and Dressler, 2013).
If roots are to be kept fresh, they can be mixed with moist sphagnum moss and stored in mesh/burlap bags or cardboard boxes under refrigeration (40∘F). Stored roots should be aerated frequently and inspected for signs of drying, mold, and spoilage (Davis and Dressler, 2013).
Roots must be properly dried in order to preserve product quality and ensure the integrity of the product during long-term storage. To dry, spread roots evenly on a wire mesh screen in a dark, well-ventilated area with adequate airflow, and where temperatures can be maintained at 85 -95∘F for 7-10 days, or until completely dried (Davis and Persons, 2014). In humid locations, temperatures as high as 130∘F may be needed to fully drive off excess moisture from the roots (Davis, 2016). The roots should be regularly inspected for any signs of mold or spoilage, and if detected, the infected pieces should be removed from the room. To determine when the drying process is complete, select several average-sized roots from the batch, and then break them in half. The roots should snap cleanly when fully dried but should not be overly brittle.
After drying, roots can be further cleaned by agitation. Because the roots shrink during the drying process, excess soil and debris that remained on the root after the initial washing become loosened and can be knocked free from the root when agitated. Since agitation can also separate many of the fibrous roots, it may be necessary to screen the debris to reclaim as much of the botanical material as possible. The size of the sifting screen used will depend on the particle size of the materials being sifted.