Caring for a Hardy Aster
Hardy Asters, an autumn-blooming perennial with little flowers resembling daisies, have so many species with so many different hybrids that over the years many of the varietal names have been lost. These colorful hybrids are often just commonly referred to as Hardy Asters, although some also have a specific cultivar name. Some common hardy asters, including Michaelmas daisies, Lilac Time, and White Niobe, are low growers reaching about 12 inches tall. Violet-blue Eventide and Harrington's Pink will grow to 4 feet tall. Other tall varieties include Mt. Everest and Mt. Rainier.
USDA Growing Zones - Asters grow in zones 3 to 9.
Bloom Colors - Asters come in red, white, blue, pink, purple and lavender, but most commonly blue to lavender.
Bloom Season - Asters generally bloom in late summer through the autumn, but some will bloom earlier.
Height - Asters generally grow 3 to 4 feet, but dwarf asters can be as small as 6 inches, and some asters will grow up to 6 feet tall, if in full sun and not pruned.
Spacing - Plant with plenty of space between to encourage air circulation and prevent mildew, approximately 3 to 4 feet apart.
Pests - Whiteflies, rabbits and aphids are common pests.
TIP: Our expert gardening advisor, Susan Patterson suggests, "Put a little dish soap in water and spray on asters to control whiteflies and aphids."
Diseases - Root rot, wilt, stem blight and leaf spot are common diseases.
Attributes - Asters attract butterflies, being a popular host plant for butterfly larvae. They will keep your garden colorful when most flowering plants have lost their blooms, and they make a good cut flower.
Companion Plants - Black-eyed Susan, Sliver Mound, Purple Coneflower and ornamental grass are good companion plants for the aster.
Soil Requirements - Asters prefer well-drained soil, slightly alkaline to acidic, depending on the variety.
TIP: Susan adds, "Hardy asters prefer sandy soil."
Sun Exposure - Asters prefer full sun to partial shade, but too much shade will squelch blooms.
Water Needs - Asters are drought-resistant, but should still be watered regularly in the mornings. Don't water leaves since asters are vulnerable to leaf fungus.
Once you've planted your Asters in the spring after the first frost, follow these care tips to insure a long and plentiful blooming season again and again.
Fertilize - Fertilizing too much is a common mistake. Over-fertilizing will result in a floppy, too tall aster that you will have to divide more often than usual. If you fertilize, do so lightly in the spring. Asters are sensitive to the soluble salts in fertilizers, and too much nitrogen will cause excessive foliage growth.
Dehead - Deadheading should be done in mid-July to encourage heavy blooming and eliminate the need for staking for taller varieties. Cut stems to one-half the size. Although, flowering will be delayed by a couple weeks, the asters blooms will be thicker and the clump more compact. Asters will self-seed, so if you don't want mass repopulation, cut off the blooms at the end of the blooming season.
TIP: Susan advises, "Cut asters to the ground after they have finished blooming and cover with a thick layer of mulch for the winter."
Divide - At the end of the growing season every couple years, pull up the plants and divide in half, removing the center and keeping the healthiest edges. Replant and mulch to protect against winter. Although asters are perennials, sometimes they have difficulty returning. Dividing gives your asters a better chance at surviving for the next season.