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Many of our favorite ornamental plants bloom in spring and summer, but fall flowers like asters are the unsung heroes of the garden. In addition to providing beautiful bright color for us to enjoy, asters offer much-needed nectar to pollinators like bees and butterflies when few other plants are blooming.
Here's how to care for these hardy, easy-growing fall flowers in your garden.
- Botanical Name: Symphyotrichum novae-angilae or Aster novae-angilae
- Common Name: Aster, New England aster
- Plant Type: Herbaceous perennial
- Mature Size: Two to six feet tall and wide
- Sun Exposure: Full to part sun
- Soil Type: Rich, well-drained soil
- Soil pH: 5.1 - 6.8
- Toxicity: Nontoxic
Plant asters anywhere from one to four feet apart. In colder climates, it's best to plant asters in spring or summer to let them get established before winter. In warmer climates, you can plant them in spring or fall.
Water plants well in warm weather, especially in the first year of planting or after dividing mature plants. Because they're so hardy, asters don't typically need additional fertilizer to grow well. But, if your soil is particularly poor, it's a good idea to add a few shovelfuls of organic compost to the hole when planting.
Asters can grow tall and leggy. Keep them contained by staking them or tying them up in the summertime. You can also pinch off growth tips in early summer to encourage fuller, bushier growth—just make sure to stop pinching back in midsummer when buds have formed.
Best Growing Conditions for Asters
Asters are hardy, weedlike native perennials. You'll often see them growing in ditches and on roadsides next to goldenrod, which tends to grow alongside asters because the contrasting colors help attract pollinators to both plants.
Because they're so adaptable, asters shouldn't be too picky about conditions in your garden. They prefer lots of sun and well-drained loamy soil to grow their best.
Types of Asters
There are about 170 species in the Asteraceae family, including chrysanthemums, marigolds, sunflowers, and zinnias. In the garden, the term "asters" typically refers to New England asters. Within that group, the main variation is in color, which ranges from pink to red to purple to blue.
How to Propagate Asters
The best way to propagate asters is by division—digging up a mature plant, splitting it into multiple clumps, and replanting. Since asters benefit from division every three years, this is a natural time to propagate your plants. Divide asters in early spring once new growth appears.
What You'll Need
- Healthy mature plant
- Gardening gloves
- Sharp, sterilized knife
- Use your shovel to dig carefully around the mother plant, lifting up the soil around the root ball. Once it's mostly free, use your hands to pick up the root ball and remove excess soil around the roots.
- Cut the root ball into at least two pieces with your knife so that each clump contains multiple new shoots as well as roots.
- Replant the divisions as soon as possible. Be sure to water new plantings consistently throughout the growing season.
Common Problems With Asters
Asters are tough, dependable perennials, but they can experience some disease issues. The best way to keep your asters disease-free is to avoid getting the leaves wet when watering, which can invite issues like botrytis blight, leaf spots, and powdery mildew.
To treat these issues, cut away excess growth (make sure to bag and throw away plant material, wash hands, and sterilize tools afterward) to allow more airflow, then apply a natural fungicide like neem oil to control the infection.
How to Get Asters to Bloom
One of the best things about asters is that they bloom in late summer and early fall when other flowers have faded for the season. Once established, it's unlikely those pretty purple flowers won't appear—but there are a few reasons your asters may not bloom.
If your plants are new and haven't established themselves, they may not bloom until next season. If your plants are mature and you haven't divided them in several years, it might be time to do so. Dividing and replanting asters can help encourage new growth and vigorous blooms.
It's also a good idea to check the bloom period for your specific variety of asters to make sure you're not expecting flowers too early. Finally, if you've been fertilizing asters regularly, lay off the feeding. Adding too much nitrogen-rich fertilizer can cause the plants to focus on growing foliage rather than flowers.
Are asters easy to care for?
Once asters are established, they are easygoing, low-maintenance plants that require minimal care.
How long can asters live?
Asters are perennial and will regrow each year with proper care. However, it's best to divide clumps of asters every three years or so to keep them healthy.
What’s the difference between asters and daisies?
New England asters and daisies (Bellis spp.) are different species in the family Asteraceae. They both have yellow centers and long, thin petals radiating from a yellow center. Daisies typically have white petals and a larger center, while the center of an aster flower is smaller, with thinner petals that are pink, blue, or purple.