Derby Canyon is a native plant nursery in Peshastin that I get some native plant starts from (drought-tolerant). They might be a good resource to consult. They mostly discourage use of soil amendments for native plants. I know from my experience that yarrow grows well from seed and doesn’t like a lo...

They might be the product of the free chipping event, but I’m not sure. I called the Twisp public works to find where the Twisp ones were deposited. Maybe check with the Winthrop public works