Whole books have been written on the subject of asters, but all you really need to know is this: their cheerful, diminutive, daisy-like flowers are among the choicest blooms of late summer and fall. Asters pick up the pace as summer flowers fade, and keep the garden going through the brilliant autumn season. They are hardy, heat- and drought-tolerant plants, great choices for butterfly gardens. Deer do not care for asters.
Individual aster flowers are small, one or two inches across, at most, but when the plants are in bloom they’re covered with pink, purple, and sparkling white flowers. Prolific-flowering ‘Purple Dome’ and many others have a bright-yellow center, like a daisy, but some have dense, feathery blooms that hide the center.
Most garden asters are mid-sized plants, from one to three feet tall. ‘Raydon’s Favorite’ and other tall asters are stately plants for the back of a flower bed, but they can be kept short (and planted up front) if you prune them with hedge shears to about 18 inches in early summer, which also encourages branching and, consequently, more blooms.
Garden designers rely on asters to produce a dazzling show in sunny spots as the gardening season winds down. They are a spectacular companion plant in hard-working fall gardens with goldenrod (Solidago), Indian blanket (Gallardia), helenium, and helianthus, and they sparkle like jewels in front of lush ornamental grasses. Asters fill in gracefully among the lanky stems of Japanese anemones, and they contribute a light and lively texture in the midst of a flowerbed full of chrysanthemums. They are very pretty planted with shimmering silver-leafed Artemisias, and among fall-blooming sedums. Asters also flourish in flowerpots.
But don’t leave them all out in the garden: asters are excellent cut flowers, dramatic in big sprays or delicate in a tiny vase on the kitchen table or on your desk. Pick them just when buds start to show color; they’ll bloom cheerfully for up to a week.