How to Plant and Grow Aster

Easy-to-grow asters 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.

Where to Plant Aster

Plant perennial 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 quantity of blooms may be reduced somewhat. 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

Although asters can be grown from seed, germination is uneven, and the results are often disappointing. It's better to purchase plants at a garden center.

In the garden, dig a hole that is larger than 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.

If you prefer to plant asters in pots, fill containers that have drainage holes with potting soil mixed with compost. They need to drain well because asters don't like soggy roots.

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, but 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

Asters that were potted in containers filled with a potting soil/compost mix and left outside for summer should be trimmed back and brought inside to a location that doesn't freeze. They should be checked occasionally to see if the soil is dry; it should remain a little moist all winter.

When there is sign 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 best ways to propagate asters. The plants will self-sow, but the resulting seedlings won't always resemble the parent and may be weak.

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.

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

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' 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 bloomer, reaching only 1 foot tall. 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.

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.

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. Some smaller ones are best grown in pots or treated as houseplants.