Purple Asters Will Fill Your Autumn Garden With Color All Season Long

Asters are the stars of the autumn garden. As summer blooms begin to fade, these native perennials explode into a riot of purple blooms that carry the garden through the autumn months. Our native asters have been cultivated for hundreds of years, generating the wide variety of cultivars available today. Some tower over the garden at five to six feet tall, while others have been tamed into tidy mounds just 18 inches across. Get to know these garden gems-learn how to grow and care for purple asters and which varieties best fit your garden style.

These beautiful native perennials also provide an important source of late-season nectar for pollinators, including native bees and butterflies. Asters serve as host plants to larvae of the Pearl Crescent butterfly and are an important food source for migrating Monarch butterflies. Songbirds feasting on seeds carry the charm of these lovely plants into the winter months.

Plant Attributes
Common Name:	Aster
Botanical Name:	Symphyotrichum spp.
Family:	Asteraceae
Plant Type:	Perennial
Mature Size:	1-6 ft. tall, 1-3 ft. wide
Sun Exposure:	Full Sun to Part Shade
Soil Type:	Moist, Well-Drained
Soil pH:	Acidic (<6.8)
Bloom Time:	Fall
Flower Color:	Purple, Pink, White
Hardiness Zones:	3-8 (USDA)
Native Area:	Eastern and Central North America
Toxicity:	Not Toxic to Humans or Pets

Purple Aster Care

Asters are adaptable plants and easy to grow in average, well-draining garden soil. Select a planting site with good air circulation to promote healthy foliage.

Light

Asters thrive in full sun, flowering best when they receive at least 6 hours a day. In hot locations, plants benefit from afternoon shade. 

Soil

Asters perform well in loamy garden soils of average fertility. New England asters and New York asters thrive in rich soil, but species from the plains states may flop if they receive too much water and nutrients. They perform well in dry or rocky soil. Most aster species tolerate clay soil.  

Water

Common garden asters thrive under moist conditions, though species differ considerably in their water needs, as described below. As a rule, water young plants regularly until established, then irrigate throughout summer during dry periods. To prevent fungal disease, water at the base of the
plant, preferably in the morning.  

Temperature And Humidity

Asters tolerate a range of growing conditions. Plants are winter hardy and stand up to summer heat and humidity. They bloom best when autumn nights are cool.

Fertilizer

Asters are not heavy feeders and usually don’t require fertilizer if grown in average to rich soil. For plants growing in nutrient poor soil, apply a balanced fertilizer in spring. 

Types of Purple Aster

Purple asters belong to the genus Symphyotrichum, a group containing over one hundred native annual and perennial species. The most common purple asters in the home garden are New England aster and New York aster, described below. Both species are native to moist eastern forests and
meadows and perform well in more northerly stretches of the Southeast. Gardeners in hotter and drier areas might turn to some of the other native asters featured here. Asters are a favorite among native plant enthusiasts, with a diversity of species adapted to the varied growing conditions found throughout the South.  

New England Aster, Symphyotrichum novae-angliae

Plant breeders refined this stunning fall bloomer into more compact, mounded forms. 'Purple Dome' is a long-time favorite, topping out at 2 feet tall. This species is well suited to gardens in the upper South (zones 5-8). 

New York aster, Symphyotrichum novi-belgii

This species prefers moist soil and tolerates salt spray, making it well suited to coastal regions in hardiness zones 4-8. Many cultivars are available with flowers ranging from soft pink to rich purple.  

Smooth aster, Symphyotrichum leave

Thriving under drier conditions, smooth aster has gained popularity among native plant enthusiasts seeking regionally adapted and drought tolerant aster species. With lovely blue-green foliage, 'Bluebird' is a popular cultivar that stands 3 to 4 feet tall. Zones 4-8. 

Aromatic aster, Symphyotrichum oblongifolium

Another drought-tolerant species for drier sites, aromatic aster (zones 3-8) thrives in poor soils and tolerates rocky or sandy planting sites. Compact cultivars include 'Raydon’s Favorite' and 'October Skies'. 

Wood’s Series Aster, Symphyotrichum hybrids

The Wood’s Series asters—including 'Wood’s Purple', 'Wood’s Blue, 'Wood’s Pink'—are hybrids known for their compact form, exceptional bloom, and good disease resistance. Hardy in zones 4-8, these adaptable asters tolerate drought and clay soils. Not to be confused with blue wood aster, Symphyotrichum cordifolium, an upland forest native. 

Eastern silvery aster, Symphyotrichum concolor

Gardeners in the warmest reaches of the South can grow asters, too! Native to sandhills and pinewoods in zones 6B-11, this unusual aster is tough as nails. The rich violet-blue flowers are produced along upright stems standing 2-3’ tall.  

How To Grow Purple Aster from Seed

Many asters can be grown from seed, and some species readily reseed in the garden, however hybrids and cultivars are typically only available as plants. The next section describes how to plant young asters in the garden, including plants you start yourself from seed.

Asters are among the easiest wildflowers to grow from seed because they do not require a period of cold temperatures to germinate. Seeds can be sown outdoors in fall or early spring, or started indoors six to eight weeks before the last frost date for your region.

To grow seeds outdoors, plant them in containers filled with potting soil or direct sow into garden beds with moist, well-draining soil in a location that receives at least four to eight hours of full sun each day. Prepare the planting bed by adding a thin layer of compost and raking the soil surface
smooth. If starting seeds indoors or in outdoor containers, use a high-quality seed starting soil mix. Look for a container about 3 to 4 inches deep with drainage holes in the bottom.

How To Start Aster Seeds:

1. Before sowing seeds, evenly moisten the soil in containers or garden beds until it is damp but not soaked.

2. Sow seeds evenly across the planting site or place 2-3 seeds per pot, covering them with 1/8-inch of soil or compost in the garden, or potting media for containers.

3. Use a mister or spray bottle to keep the soil moist but not wet.

4. Seedlings will emerge in 1-3 weeks, depending on species. Thin seedlings sown in planting beds to a spacing of six to eight inches.

5. Transplant seedlings grown indoors into the garden or outdoor containers after the threat of frost has passed. Seedlings grown in outdoor containers can be moved to the garden when they are 3-4” tall.

How To Transplant Purple Asters Into The Garden

Many different aster species and cultivars are available as young plants from your local garden center. Because these are most often grown in a greenhouse, you want to wait to transplant young plants into your garden after the danger of frost has passed. The same is true for any seedlings you started indoors from seed. Whether you start your plants from seeds or purchase asters from the garden center, seedlings will benefit from a period of hardening off prior to being planted in the garden.

Hardening off slowly acclimates plants to outdoor conditions to avoid shocking them with the drastic change in environment. Begin hardening off seedlings about one week prior to transplanting outdoors. Expose young plants to outdoor conditions during the day by placing them in a protected location, out of direct sunlight and wind. Increase the length of time aster seedlings are outside each day and slowly increase exposure to sunlight and wind. By the end of the week, plants can be set in full sun and left outside overnight. Pay attention to watering as plants will require more water outside due to wind and higher temperatures.  

Once aster plants are hardened off, they can be transplanted into the garden after all threat of frost has passed. Space plants according to their mature width, 1 to 3 feet apart, depending on the species.

1. Dig a planting hole large enough to accommodate the root ball of the plant.

2. Gently remove the plant from its pot and loosen the roots if they are tightly bound.

3. Set plants at the same depth they are growing in their containers.

4. Fill the planting hole with soil, pressing the soil down gently with your hand. 

5. Water plants thoroughly and mulch with a 1- to 2-inch layer of organic material such as compost, cocoa bean hulls, or wood chips.   
   

Pruning Purple Aster

Asters benefit from being pinched or cut back in early summer to promote denser growth and more flowers. Cut back plants by up to one third in mid to late June. Do not pinch after early July or you risk removing flower buds. Many asters grow quite tall and may require staking to keep from flopping over. Pinching back plants can help reduce the need for staking. Deadhead plants after flowering if you do not want your asters to self-sow in the garden. 

Propagating Purple Aster

Asters can be propagated from seed, cutting, or division. Plants grown from seed take a long time to reach a sizeable, flowering plant. Division is the simplest way to multiply plants. Dividing asters not only produces new plants, but also benefits existing plants and keeps their size in check.  

Like other fall-blooming perennials, asters are best divided in spring, rather than fall. Dig plants in early spring when the ground has thawed and plants begin to break dormancy. Separate the crown into multiple 6- to 8-inch sections, making sure each portion has roots and shoots. Replant divisions immediately and keep them well watered to establish.  

New plants can also be propagated from cuttings. Clip 2- to 4-inch sections of young, tender stems in spring. Remove the cutting’s lower leaves and dip the cut end in a rooting hormone. Plant cuttings in containers filled with moist, light weight potting media and cover the pots with a perforated plastic bag. Mist plants as needed to maintain soil moisture. Cuttings will root within a few weeks. New plants can be hardened off and planted outdoors in fall. 

Common Problems

Asters are susceptible to powdery mildew, a fungal disease that covers leaves in white powdery-looking growth. Severe infections can cause foliage to drop from plants. Good air circulation helps reduce the incidence of powdery mildew. Improve air movement through the plant canopy by spacing plants farther apart and selectively thinning branches as appropriate. 

The best way to avoid powdery mildew is to plant disease-resistant varieties. Smooth aster cultivars like 'Bluebird' and 'Calliope' have excellent mildew resistance, as do aromatic asters. The Wood’s series asters also have good disease resistance. New England asters tend to be more susceptible than other aster species, while disease resistance among New York asters varies considerably by cultivar. Seek out varieties with proven resistance.