Hi, A B!
I planted both blue and black cohosh plants from Companion Plants this past year. I am USDA zone 4b, but most reliably zone 3. By this past fall (their first year) both plants were still quite small, I’m sure it would kill them completely to get any root, and I wouldn’t have gotten much root material at all after this first year based on the plant size above ground. So, it would depend I think on how many plants you grow and how much root material you want to harvest. I’m crossing my fingers that mine get bigger before I try harvesting any.
Hope this helps! 🙂
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