Asters are hardy, easy-to-grow perennials that come in a variety of shapes and sizes to suit gardens of all dimensions, shapes, and styles—especially cutting gardens and sunny or lightly shaded borders. Although a few species bloom in early spring, most put on a spectacular flower display, supported by evergreen foliage, from late summer well into fall, when other summer blooms are fading.
Daisy-like aster plants get their name from the Latin word for "star," and their flowers are often the superstars of the fall garden. Some asters reach 6 feet tall with flowers that are white, pink, rich purple, showy lavender, and occasionally blue.
Aster Overview
Where to Plant Aster
Plant asters in full sun to partial sun in a bed with moist, well-draining soil in Zones 3-9. Asters like cool days and nights, so if you live in a warm climate with hot temperatures, partial sun is a good choice, even though the number of blooms may be somewhat reduced.
Plant medium and tall asters in the middle and back of garden beds, while short ones grow well in borders. Asters are excellent for cutting gardens. They can also be planted in containers.
How and When to Plant Aster
Unless you are after a specific aster variety, it is usually the most convenient to purchase plants from a garden center instead of starting your asters from seed.
Dig a hole twice the diameter of the nursery pot. Add compost to the soil to improve drainage. Remove the plant from the nursery container and set it in the hole at the same height it was in the nursery container. Backfill with soil and compost and press down to remove air bubbles.
Space the transplants 1 to 3 feet apart, depending on the species. Add mulch around the plants to keep the soil cool and prevent weeds, and water generously. Pinch back the tips of young plants to encourage bushiness. If your region receives less than 1 inch of rain a week, water the asters regularly.
Aster Care Tips
Asters are easy to grow when their basic needs are met.
Light
With several hundred species available, asters can be found for most growing conditions short of full shade. Most asters should be grown in full sun to prevent flopping, especially in shady or windy locations. Woodland species tolerate shade but need morning sun to produce the prettiest flowers.
Soil and Water
This plant prefers moist, well-drained soil; overly wet soil leads to rot. Some asters require nutrient-rich soil; others need lean soil lacking organic material.
If your plants lose flowers or are not flowering well, they are receiving too much or too little moisture. Try a different watering method or schedule.
Temperature and Humidity
Asters prefer cool temperatures for day and night and are frost-hardy. Gardeners who live in hot areas should plant in an area that receives some shade. Asters have no special preferences regarding humidity levels.
Fertilizer
Asters are moderate feeders and excessive fertilizer shortens the bloom period. Apply a balanced flower fertilizer according to product directions every two weeks beginning in spring and continuing until flowers start to open. Stop fertilizing the plants in August.
Pruning
Remove spent flowers after the asters are finished blooming for the season to prevent spindly unwanted seedlings that may not resemble the original plant. Asters are self-seeders if you leave the flowers on the plants.
In the spring, remove any damaged foliage or stems. In midsummer, cut the stems back by half to encourage more blossoms in fall. Some gardeners cut back their asters plants to 2 inches above the soil line after they finish blooming in fall, but gardeners in colder areas leave the dead stalks and foliage in place to protect the roots during winter.
Potting and Repotting Aster
Use containers with large drainage holes and fill them with a combination of potting soil and compost. Water them regularly, as container plants dry out much faster than plants in garden soil.
Potted asters that are winter-hardy in your zone don't need to be overwintered. However, to protect their roots from the cold. the pots should be moved to a sheltered location such as an unheated garage or shed, or buried in the ground for better insulation. Check them occasionally to see if the soil is dry; it should remain a little moist all winter.
When there are signs of new growth in spring, repot the asters with a fresh potting soil/compost mix. Harden them off before moving them outside and keep the planting medium moist.
Pests and Problems
Watch for powdery mildew and rust diseases on the leaves of asters. Chrysanthemum lace bugs and spider mites sometimes show up and suck nutrients from the leaves, but they can be controlled with insecticidal soap.
How to Propagate Aster
Cuttings and divisions are the easiest ways to propagate asters. The plants will self-sow, but since many asters are cultivars. the resulting seedlings won't always resemble the parent.
Division: Divide clumps of asters every few years in spring as soon as new growth appears. Dig up the plant or clump of plants with a sharp spade and divide it into several sections with the spade or sharp shears, making sure each section has healthy roots and foliage. Replant the divisions immediately and water them.
Cuttings: In spring, take 4-inch cuttings from the plant's stem tips. Remove the leaves from the bottom half of each cutting and dip it in rooting hormone. Put each cutting into a small pot filled with loose potting soil. Cover each pot with a clear plastic bag with air holes punched in it. Put the pots in a bright area (not in full sun) and keep the soil moist until the plants root. When you see any new growth, remove the plastic bag.
Asters have undergone a botanical reclassification after botanists studied the plants' morphology and DNA. Now only aster species native to Europe and Asia are in the Aster genus whereas the aster species native to North America belong to two other general, Symphyotrichum and and Eurybia. The common name is still aster for all the plants.
Types of Aster
Aster varieties range from 1 foot to 6 feet tall, so there's a size that will fit anyone's garden.
'Alma Potschke' New England Aster
KRITSADA PANICHGUL
Symphyotrichum novae-angliae 'Alma Potschke' blooms from August to frost with red-violet daisies on a plant 4 feet tall. Zones 4-8
Calico Aster
Symphyotrichum lateriflorum is a 2- to 3-foot-tall mounded, shrubby plant with pinkish-white daisies in September and October. Zones 4-8
'Fellowship' New York Aster
Symphyotrichum novi-belgii 'Fellowship' has clear pink daisy flowers on plants that reach 3 feet tall. Zones 4-8
'Purple Dome' New England Aster
Symphyotrichum novae-angliae 'Purple Dome' grows only 18 inches tall and has bright purple flowers in September and October. Zones 4-8
'Monch' Aster
Symphyotrichum x frikartii 'Monch', a hybrid aster, forms a tidy mound 2 feet tall and wide with lavender-blue semidouble, daisy-like flowers from June to September. Zones 5-8
'Triumph' Aster
Symphyotrichum x alpellus 'Triumph' is a petite summer-blooming hybrid reaching only 1 foot in height. Its compact form is ideal for the front of the border or container gardens. Zones 4-9
'Wonder of Staffa' Aster
Symphyotrichum x frikartii 'Wonder of Staffa' is similar to 'Monch', but it grows 28 inches tall and has paler blue blooms. Zones 5-8
'Hella Lacy' New England Aster
Symphyotrichum novae-angliae 'Hella Lacy' grows 3 feet tall and features clear purple flowers from midsummer through fall. Zones 4-8
Aster Companion Plants
Boltonia
Boltonia is a large, late summer showstopper that looks almost like a tall baby's breath in a perennial border. Also known as white boltonia and white doll's daisy, its 1-inch-diameter daisy-like blooms may be white or light pink. Cut it back in early summer to promote a sturdier branched plant that requires no staking. Zone 3-10
Russian Sage
With its tall wispy wands of lavender or blue flowers and silvery foliage, Russian sage is an important player in summer and fall gardens. It shows off well against most flowers and provides an elegant look to flower borders. The aromatic leaves are oblong and deeply cut along the edges. Foot-long panicles of flowers bloom for many weeks. Excellent drainage and full sun are ideal, although very light shade is tolerated. Plant close to avoid staking since the tall plants tend to flop. Zone 4-9
Sedum
Sedums are nearly perfect plants. They look good from the moment they emerge from the soil in spring and continue to look fresh and fabulous all growing season long. Many are attractive even in winter when their foliage dies and is left standing. They're also drought-tolerant and need very little, if any, care. They're favorites of butterflies and useful bees. The tall types are outstanding for cutting and drying. There are lots of varieties, from tall types that top 2 feet to low-growing groundcovers that form mats. All thrive in full sun with good drainage. Groundcover types do a good job of suppressing weeds but seldom tolerate foot traffic. Zone 3-10
Frequently Asked Questions
- When do asters bloom?Most asters bloom from August through October and sometimes longer, depending on the variety and climate.
Most asters bloom from August through October and sometimes longer, depending on the variety and climate.
- Are asters good for pollinators and wildlife?Asters attract lots of late-season pollinators, including bees and butterflies. In the winter, they provide food and shelter for small animals and birds. Deer leave them alone.
Asters attract lots of late-season pollinators, including bees and butterflies. In the winter, they provide food and shelter for small animals and birds. Deer leave them alone.