Aster Flower Plant Profile

aster flowers

The Spruce / Adrienne Legault

It's a cruel trick of Mother Nature that that most glorious weather of the gardening season coincides with the decline of most blooming plants. Asters, however, don't play along with the prank. Like garden mums, asters flower in response to the shortening days of fall, giving gardeners a beautiful display of daisy-like flowers that can bloom from August through October. Asters comprise many species in several different genera of plants, as well as dozens of cultivars, but for gardeners, asters are simply those great flowers that provide purple or blue daisy-like flowers late in the season.

Although home and garden centers often market asters as a seasonal impulse purchase among displays of pumpkins and hay bales, asters are long-lived perennials that you'll want to make a permanent part of your landscape. Though aster flowers have that wildflower look, they are also beautiful in cut-flower arrangements. People aren't the only ones who find asters attractive; pollinators such as bees and butterflies also love aster flowers. If they're planted in the fall, asters can be a rare source of late-season nectar, making them a crucial flower for pollinators.

Asters can be planted almost any time of the year, though spring is a typical planting time since this is when potted nursery plants are most available. These fast-growing perennials will be ready to put on a good fall display in their first year, and once established, they will hold their own for many years.

Botanical Name Aster spp. Symphyotrichum spp.
Common Names Asters, michaelmas daisies, frost flowers
Plant type Herbaceous perennial
Mature Size 1 to 6 feet tall; 1- to 4-foot spread (varies by type)
Sun Exposure Full sun
Soil Type Loamy, well-drained soil
Soil pH 5.8 to 6.5 (slightly acidic)
Bloom Time Late summer and fall
Flower Color White, red, pink, purple, or blue
Hardiness Zones 3 to 8 (USDA); varies by species
Native Area Meadows of North America and Eurasia
butterfly on asters

The Spruce / Adrienne Legault

asters

The Spruce / Adrienne Legault

close up of aster

The Spruce / Adrienne Legault

A honey bee investigates an aster
lkordela/Shutterstock

How to Grow Aster Flowers

While you can grow aster flowers from seeds planted in the springtime, it may take several years for them to mature into full-sized plants. More often, asters are planted from potted nursery specimens. They do best in a loamy, well-draining soil. Give a good amount of space around the plants to allow space for the roots to expand.

Every three years or so, the root clumps should be dug up and divided to keep the plants from getting too woody and dying out in the centers. The woody center can be discarded, with the outer portions replanted.

When frost finally kills off the foliage, clip off the stems at ground level. Or, this can be done in the spring to allow birds to feed on the flower seeds over winter. Finches and chickadees are especially fond of aster seeds.

Light

Choose an area with full sun for your aster flowers. Too much shade will cause lanky plants and fewer flowers, especially for the common cultivars and hybids. There are some native species varieties, however, that will do quite well in part shade conditions.

Soil

Asters appreciate loamy soil on the slightly acidic side, with a pH ranging from 5.8 to 6.5. If your soil is alkaline, you can correct it by adding organic matter such as well-rotted manure, leaf mold, or compost.

Water

Keep new plantings moist and continue watering until the flowers are finished blooming. One thing to note: Try to water the base of the flowers without splashing water on the leaves. Doing so may cause mildew or fungal growth. One inch of rain or watering once a week is usually recommended for most perennial plants.

Temperature and Humidity

Aster flowers generally do better in cool and moist climates.

Fertilizer

Asters are moderate feeders, and they appreciate a balanced flower fertilizer given twice a month from spring until the blooms begin to open. Excessive nutrients can shorten the blooming time, so stop fertilizing asters in August.

Propagating Asters

Asters can be propagated by collecting seeds or rooting stem cuttings, but by far the easiest way is by simply digging up the root clump, dividing it into pieces for replanting. The woody center portion of the clump should be discarded. The clumps will survive no matter when you perform the division, but if done in late fall or early the following spring, the plants will become established enough to put on a fall display in their first year.

Aster roots are tough, so you will need to use a sharp spade to cut the clumps into pieces. Water thoroughly immediately after replanting, and feed the divisions with bone meal to provide phosphorus for immediate root growth.

Varieties of Asters

The taxonomy of asters is somewhat complicated, as it now includes several genera of plants, all within the Asteraceae family. At one time, all the species were considered part of the Aster genus, but several species have now been reassigned to the Symphyotrichum genus. The flowers known as New England asters, for example, now belong to Symphyotrichum and are known as S. novae-angliae. And New York asters are now formally known as Symphyotrichum novi-belgii.

Finally, a number of species still belong to the original Aster genus, including hybrid crosses and their named cultivars. A. amellus and A. thomsonii are two frequent parents used in the hybrid cultivars commonly sold in the nursery trade.

Most gardeners do not need to worry too much about the toxonomical details, as all these plants are sold as asters and all have the familiar daisy-like flowers and perform the same way in the garden. The original species were wildflowers found in North America and Eurasia, but modern garden varieties are usually hybrids bred to produce new colors and tidier plants. Some of the more popular cultivars include:

  • 'Celeste': Early blooming; dark blue flowers with bright yellow centers
  • 'Hazy': Early raspberry-pink flowers with yellow centers
  • 'Puff': A white aster hardier than many other white cultivars; very early blooms
  • 'Professor Kippenburg': Clear blue flowers on a compact plant
  • 'Winston Churchill': Early bloomer with dark pink flowers

Common Pests/ Diseases

Rust and powdery mildew disease can affect aster foliage. Follow proper plant spacing to improve air circulation, and avoid splashing watering to prevent these problems.

Most insect pests leave asters alone, but lace bugs can be a bother. You're more likely to notice the damage they cause than the insects themselves, which are very small and a nondescript grayish-brown color. If you notice yellowing foliage and leaf drop in the summer, consider using insect soap on the plants. Make sure to coat all sides of the foliage to impact the hiding pests. Fortunately, lace bug outbreaks precede aster blooming time, so spraying won't affect butterflies and bees.