How to Grow Asters

aster flowers

The Spruce / Adrienne Legault

In This Article

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 buds that can bloom from August through October. Native to North America, asters comprise many species in several different genera of plants, as well as dozens of cultivars, but for gardeners, asters are simply 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 purchase among displays of pumpkins and hay bales, asters are long-lived perennials that can become 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 planted in the fall, they 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 typical since that's when potted nursery plants are readily 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 Symphyotrichum
Common Names Asters, New England asters, frost flowers
Plant type Herbaceous perennial
Mature Size 1–6 ft. tall, 1–4 ft. wide (varies by type)
Sun Exposure Full sun
Soil Type Loamy, well-drained
Soil pH Neutral to acidic
Bloom time Summer, fall
Flower Color Purple, pink, blue, white
Hardiness Zones 3–8 (USDA)
Native Area North America
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Aster Care

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 loamy, well-draining soil, and desire a good amount of space around the plants to allow space for their 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. This can also be done in the spring to allow birds to feed on the flower seeds throughout winter—both finches and chickadees are especially fond of aster seeds.

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

Light

Plant our aster flowers in an area that boasts full sun for the majority of the day. Too much shade can cause lanky plants and fewer flowers, especially for the more common cultivars and hybrids. There are some native species varieties, however, that will do quite well in partially shady conditions.

Soil

Asters appreciate loamy soil that's slightly acidic, 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 regularly until the flowers are finished blooming. As a rule of thumb, the soil your asters reside in should stay consistently moist but never saturated. One thing to note: Try to water the base of your asters without splashing water on the leaves—doing so can 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 thrive in cooler temperatures and are frost hardy, able to withstand near-freezing temperatures temporarily. When it comes to humidity, asters have no special preferences and therefore will not need increased humidity levels or extra spritzing.

Fertilizer

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

Aster Varieties

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 taxonomical 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': These dark blue flowers bloom early and feature bright yellow centers.
  • 'Hazy': Another early bloomer, the "hazy" aster boasts raspberry-pink flowers with yellow centers.
  • 'Puff': The puff aster is hardier than many other white cultivars and will bloom among the earliest.

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 and 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.

Common Pests/ Diseases

Rust and powdery mildew disease can affect aster foliage. Follow proper plant spacing recommendations 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 spot yellowing foliage and leaf drop in the summer, consider using insect soap on the plants, coating 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.