This is new to me. Apparently proso millet (Panicum miliaceum) is being sold as a prime growing medium for mushroom cultivation. Came across one product advertising this, and found a couple of others by web search: * North Spore Bulk Organic Millet Grain for Mushroom Cultivation https://northspore.com/products/organic-millet-for-grain-spawn-production-an... * Olympus Myco White Proso Millet https://www.olympusmyco.com/products/white-proso-millet-unhulled * Champignonz White Proso Millet https://champignonz.com/products/white-proso-millet-25lb * Outgrow White Millet https://champignonz.com/products/white-proso-millet-25lb Each page has a bit of a description, but this one discusses why (proso) millet is "often regarded as the gold standard for growing mushrooms": * Rootlab, "Rye or Millet: What’s the Better Grain Choice for Mushroom Cultivation" https://www.rootlab.com.au/learn-about-mushroom-grains/rye-or-millet-whats-t... There's certainly more to this. but I'll leave it here. Don Osborn, PhD (East Lansing, MI, US) North American Millets Alliance