Of the many types of Achillea grown in gardens, some are suitable for rockeries while others are fabulous, easily grown hardy perennials for beds and borders. The flower heads of Achillea, which bloom for a long period during the growing year, can be either loose clusters or flat heads comprised of a mass of tiny daisy-like flowers. With the common name of yarrow, Achilleas grow from rhizomes, which give them the ability to spread (but not invasively), while still being either upright or mat-forming in habit. They look good with grasses and prairie-style plants, whereas the fern-like foliage and cow-parsley type flower heads also enable them to blend with cottage or woodland-style plants. When Achilleas die back at the end of the year, they dry out fully, giving great structure to the garden — they are often used in dried flower arrangements!