How to Grow and Care for Aster Flowers

In this article, you will learn to grow perennial late season asters in your outdoor living space, you’ll find a wide assortment of species and cultivated varieties from which to choose, and you’ll also discover some unique plants that are called asters, but don’t fit the general description.

Here’s what’s in store:

We’ve got a lot to cover, so let’s get started!

Cultivation and History

At one time, almost 600 aster-like perennial flowers were classified as asters. However, the botanical taxonomy was revised in the 1990s, and now about 180 varieties native to Asia and Europe are classified as “true” asters.

With the botanical reclassification, North American species were regrouped into various genera, including:

• Doellingeria
• Eurybia
• Ionactis
• Symphyotrichum

However, all are still called asters in common parlance, and it is not uncommon to find many identified by their original classifications in horticultural and merchandising literature.

The word “aster” is Latin for star.

Another common name for the fall-blooming perennial varieties is the “Michaelmas daisy.” It is derived from the flowers’ bloom time, which is often around the Christian feast day of St. Michael on September 26th. This name remains popular in Britain.

Wild species range in height from the three- to six-inch heath type, S. ericoides, with a spread of three to 12 inches, to three- to six-foot New York, S. belgii, that spreads two to three feet across.

Cultivated varieties are often more compact and feature enhancements such as disease resistance, wider zone suitability, and greater shade tolerance.

Plants grow in a clumping fashion and have upright stems.

The North American types have sprays of multiple blossoms at their terminal ends, with diameters of one-half to one inch across.

European and Asian species have fewer, larger flowers per stem that measure approximately two inches across.

The stems are green or brown, hairy or smooth, and sometimes woody.

The foliage is green and may vary, with unique characteristics such as hairy or smooth, deeply serrated or smooth edged, broad or narrow, heart-shaped, or bronze in the fall.

The flowers have a daisy-like yellow center disc that contains florets, or many small flowers. In some species, it turns red-brown during the growing season.

And as mentioned, the rays, or petals, are blue, pink, purple, or white.

Plants tend to be vigorous growers that naturalize via shallow roots and self-sowing. Cultivated varieties may produce seed that is not viable, or that produces characteristics and plants with a level of quality that differ from the parent from which they came.

A Look Back

Historically, the leaves of some species were used by herbal practitioners. Those of the New England S. novae-angliae were often used to relieve pulmonary distress.

By the 1700s, British plant hunters brought wild and wooly North American native species back to England to breed new and exciting cultivars.

By the 1800s, a cultural shift from formal to more informal gardening in England’s botanical showplaces boosted the flowers’ popularity.

And in the 20th century, commercial production brought new innovations in flower color, size, and form, as well as height.

A Broad Range

Today, we enjoy an ever-increasing variety of cultivars suited to home gardening. And that weedy flora the British botanists sought is now appreciated for its essential role in providing habitat for local wildlife, especially the beneficial pollinators that evolved with and depend upon them in their native settings.

One species endemic to Europe that has remained prevalent in the wild is the Italian aster, Aster amellus, a widely hybridized variety with many cultivars.

It is one of the exceptions to the norm that we mentioned at the outset, and grows best in Zones 3 to 10 with slightly alkaline soil.

However, others that are seldom cultivated sometimes become quite rare, like the North American serpentine species, S. depauperatum.

And finally, to round out our introductory deep-dive into this large group of plants, in addition to the perennial fall-blooming types, there are others that fall under the aster umbrella, including the spring-blooming perennial Alpine, A. alpinus, the midsummer to fall blooming annual China aster, Callistephus chinensis, and the spring to midsummer blooming Stoke’s, Stokesia laevis.

As you can see, when we say, “aster,” we may be referring to any of a host of flowering floral species, many of which are unrelated to any of the qualifying genera. When shopping, specify “perennial late-season” or “fall-blooming” to find what you seek.

Propagation

To grow your own fall-blooming perennial asters, you’ll need to start with seeds, soft stem cuttings, divisions, or nursery plants. Let’s explore each method.

From Seed

Start seeds indoors about four weeks before the last average spring frost date for your region.

Use biodegradable seed starter cells filled with a good quality potting medium. 

Sow one or two seeds per cell.

Barely cover the seeds with 1/8 inch of potting medium.

Maintain even moisture, but do not oversaturate.

Place the cells in a sunny location.

When the seedlings have two sets of true leaves, thin them to one per cell.

After the danger of frost has passed, set the cells outside for a few hours a day for three to four days to “harden off,” or acclimate to the outdoors.

Transplant the seedlings to the garden or containers that can accommodate mature dimensions.

Place entire starter cells into the ground so that the seedlings are at the same depth they were in the starter cells.

Tamp down and water to secure them in the ground.

Maintain an inch of water per week in the absence of rain.

Alternatively, you may direct sow seeds after the danger of spring frost has passed.

At season’s end, you can also harvest seeds for later planting. However, remember that only true species, not cultivated varieties, produce replicas of a parent, and some hybrids are sterile.

From Soft Stem Cuttings

One way to replicate the traits of a parent is to take soft stem cuttings from an existing plant.

The best time to do this is in late spring or early summer.

You’ll need to use sanitized pruning shears to cut a six-inch length of the topmost portion of a soft, young stem.

Remove the leaves from the bottom three to four inches of the stem.

Dip the cut end of the stem into rooting hormone powder.

Place the dipped cutting into a biodegradable starter pot filled with rooting or a porous potting medium, burying it to a depth of two to three inches.

Maintain even moisture, but don’t let it get soggy.

Place the pot in a sunny location.

An optional action you may take is to cover the pot loosely with a clear plastic bag to create a mini greenhouse. Just take care to keep it out of direct sunlight that may cook the foliage.

When you see new growth, you’ll know that cuttings have established roots and you can transfer the entire starter pot to the garden or a permanent container.

Be sure to set the starter pot into the soil so that its surface is at ground level.

By Division

Another way to multiply a favorite variety is by digging up an established clump and cutting it into two or more sections that can be replanted as desired.

Please consult our guide to dividing perennial asters for instructions.

While many asters form woody clumps, others do not. When you dig up non-woody types, you have the option of cutting the clumps into sections with multiple shoots, or of teasing the soft-stemmed individual shoots apart to be planted singly.

From Nursery Plants

Local and online nurseries offer established potted varieties for transplant to the home garden.

Upon purchase, unpot the plant. Leaving the majority of the potting soil attached, gently loosen any compacted roots, and settle it into the ground at the same depth it was in the nursery pot.

Tamp the soil, water well, and maintain moisture with an inch of water per week.

How to Grow

After the last average frost date of spring, find a sunny to partly shady location with average to organically-rich soil that drains well. As mentioned, the ideal pH is slightly acidic, within a range of 5.1 to 6.8.

Contact your local agricultural extension about doing a soil test to determine the characteristics of the earth in your landscape.

Work the soil to a depth of eight to 12 inches. Amend as needed with compost to increase the acidity a bit and improve soil quality and drainage. A little sphagnum peat will also increase acidity.

Depending upon mature dimensions, you’ll need to sow seed or transplant stem cuttings, divisions, or nursery plants between eight and 36 inches apart to allow for their maximum widths.

Proper spacing promotes good airflow and inhibits humidity buildup and fungal spore activation.

For seeds, sprinkle some at the appropriate intervals, bury them in 1/8 inch of soil, and thin seedlings to one per interval when they have two sets of true leaves.

For stem cuttings, divisions, and nursery plants, space them, and settle them into the ground at the same depth they are growing in their original containers.

If you are growing in containers, be sure to choose those that can accommodate mature dimensions, plus an inch for your watering can spout to fit. As the roots are shallow, a depth of 12 inches should accommodate most types.

Once planted, apply a well-balanced, slow-release, all-purpose granular fertilizer per package instructions. Sprinkle it on the soil near but not on the stems, to avoid burning them.

You may add a two-inch layer of mulch around but not touching the stems, to aid in moisture retention and weed control. Keep it at a distance to discourage fungal development at the stem bases.

After the first year, landscape plants only need supplemental water in dry spells. As for container gardening, you will need to remain vigilant, as pots dry out quicker than ground soil.

By the time fall comes, your flora will be firmly established and ready for winter.

Growing Tips

• Maintain even moisture during germination and discontinue watering once established, except during dry spells.
• Space to accommodate mature dimensions and inhibit fungal growth.
• Save seeds if you like, but don’t expect them to produce the quality or characteristics of the parent.
• Take care not to oversaturate the soil, as that opens the door to fungal spore development.

Pruning and Maintenance

In early spring, fertilize with an all-purpose, slow-release, well-balanced granular product. Sprinkle it around, but not touching the stems, and water it in.

Spring is also the time to change the layer of mulch, taking care to leave airspace around the stems to inhibit fungal growth.

Keep the garden weeded during the growing season, to inhibit competition for water and deter pests and pathogens. Mulch aids in this endeavor.

For first-year plants, maintain an inch of water per week. Water established ones during dry spells, as needed.

Early on, between late spring and early summer, pinch back the growing tips by one-third. This encourages more bushy, less leggy growth, lateral stems, and blooms.

As plants mature, it may be necessary to stake tall ones with sticks and twine, to keep them from flopping over.

And as flower stems finish blooming, you may want to prune them off to limit the self-sowing of seeds.

You can read about pruning perennial asters here.

For most varieties, dividing every three years or so is advised. For extremely vigorous growers, you can do it every year. Dividing restores vigor, resulting in better flower production.

Please see our guide to managing asters in the garden for even more ways to care for your flowers.

In addition to these species and cultivars, some others you may like are:

• Purple early-spring blooming Alpine aster, A. alpinus.
• Annual China aster, C. chinensis, in an array of colors and bicolors.

• Purple late-blooming Tatarian, A. tataricus, with its preference for slightly alkaline soil.
• White wood, Eurybia divaricata, a low-water species that tolerates drought, heavy shade, and poor soil. 
• Smooth, S. laeve, a blue to lavender, full sun, low-water, drought tolerant species.

There are options for everyone, with some cultivars having larger, brighter flowers, and others more reminiscent of their wildflower forebears, with what seem like clouds of tiny pastel blossoms.

With so many to choose from, take care to check details such as recommended growing zones, soil pH, and tolerance for shade when selecting the perfect blooms for your landscape.

Also, select products that have been bred for superior disease resistance when possible.

Managing Pests and Disease

When you start with quality products, especially those bred to be highly resistant to pests common to Asteraceae flowers, you have the best chance of having few problems.

However, circumstances beyond our control, like summers with heavy rainfall, may foil our best efforts.

Some pests to watch for are:

• Aphids
• Chrysanthemum Lace Bugs
• Cucumber Beetles
• Leaf Miners
• Nematodes
• Slugs and Snails
• Tarsenoid Mites

Common diseases include:

• Aster Yellows
• Leaf Spot
• Powdery Mildew
• Rust
• Stem Canker
• White Smut

One way to inhibit insects and the pathogens they carry is by planting diverse flora that attracts beneficial pollinators that feed on pests.

Another way is to divide clumps every few years to optimize their health and resistance, and to move them to new locations. This decreases exposure to fungal spores that may winter over from previous years.

Best Uses

With their abundance of small to tiny blooms, fall-blooming perennial asters are considered a “filler” flower in the floral industry.

Their form lends itself to filling gaps between other plants, especially as summer specimens wane and leave spaces in the garden.

The larger species and cultivated varieties make great backdrops at the backs of beds, and especially in front of foundations.

They also do quite well with other tall seasonal species that lend each other support and look well in mixed meadows.

Planted en masse, the blooms merge into soft swaths of color that play well with other seasonal perennials as well as autumn leaves.

The more plants you have, the bigger the “cloud” of color is that you create.

For small to midsize types, front of bed and border as well as container placements work well. 

One aspect of these vigorous bloomers to be aware of is that they tend to lose their lower leaves when they experience water stress, usually from hot temperatures and dryness, but sometimes from oversaturation.

Here in the Northeast, I see this late in the season, when we have a resurgence of summer heat and humidity. The bottom foliage yellows and drops, leaving unsightly bare “legs.”

To anticipate this and not have an eyesore on your hands, place smaller seasonal flora in front to shield the lower stems in butterfly, cottage, and cutting gardens.

There are many excellent companion plants for asters that share similar cultural requirements for sun, soil, and water, including:

Mixed groupings that include asters enjoy its lush foliage throughout the summer. Then it bursts into bloom as a backdrop to late-season specimens.

Those with contrasting colors, vertical heights, and robust textures make for appealing contrasts.

Don’t forget to pair your favorites with compatible ground-covering plants, as this is another way to keep water-hogging weeds at bay.

And finally, some species, as noted, are very tolerant of dry conditions and poor soil, making them suited to rock gardens and xeriscaping.