Three perennials that get A plus grades in my garden are achillea, otherwise known as yarrow, antirrhinum or snapdragon and astilbe. My first awareness of achillea was the roadside weed, or wildflower, depending on your point of view. Roadside yarrow is usually white with the typical achillea flat topped cluster of tiny flowers. The ferny green foliage is pretty even when the plant is not in bloom. When I began to learn about perennials from my garden mentor…