Yarrow can be propagated by seeds or root divisions in the spring or fall. Space the plants ten to twelve inches apart as they will spread. Yarrow does much better growing in full sun and in slightly acidic soil. Light, shade, competition, other plants in the neighborhood, plants that grew there before, soil type, soil acidity, soil nutrients, moisture, soil depth, wind exposure, and some things I haven't thought of may influence a plant's ability to thrive or even survive. Acceptance of what works may be the best advice I can offer.
Wild flowers are wonderful in the wild or as part of a home flower garden.
I even like to appreciate them in my lawn. Thanks for asking. Mort is a husband and father. He authored a book, Gardening For Independence and was named Environmentalist of the Year by Down East Magazine in 1987. He is a consultant for organizations.