How to Grow Aster
Asters are the stars of the fall garden. Their beautiful daisy-shaped white, pink, blue, purple or red colored flowers bloom in the garden when little else is flowering.
Aster are important plants in gardens, wildflowers meadows and roadsides because they are one of the latest-blooming nectar plants for bees and butterflies. They should be a mainstay in any pollinator garden for this reason.
When & Where to Plant Aster
Light: Asters grow and flower best in full sun. Some varieties will tolerate part shade but will have fewer flowers.
Soil: Asters grow best on well-drained, loamy soil. Wet clay soil will lead to root rot and dry sandy soil will lead to plant wilt.
Spacing: Depending upon the variety, space plants 1 to 4 feet apart.
Planting: Plant asters anytime during the growing season. In the South, spring and fall are best to allow the plant to get established before severe hot or cold weather. In the North, plant anytime up to early fall. This will allow the roots to get established before winter.
How to Grow Aster Throughout the Season
Growth Habit: Asters grow 1 to 6 feet tall and 1 to 4 feet wide depending on the types and variety. The plants are upright and bushy with hairy or smooth leaves and daisy-like flowers.
Staking: Stake or cage tall varieties of asters, such as the New England asters, in midsummer to keep the plant from flopping over in fall.
Watering: Keep young plants well-watered. Water established plants in summer during dry periods. Plants that are drought-stressed may not grow as strongly or flower as well in fall.
Fertilizing: Asters usually don't need much extra fertility if grown on fertile soils. Annually add compost in spring along with a ½ cup of an organic balanced fertilizer.
Mulching: Asters are hardy plants and can survive winters in zone 4 easily. Mulching is necessary only on dry soils to maintain soil moisture levels, to prevent weeds, and to protect those varieties that are marginally hardy in your area. Add a 2 to 3-inch thick layer of shredded bark mulch around the base of the plant in spring. Don't allow the mulch to pile up around the stems or it may cause the crown to rot.
Trimming & Pruning: Asters don't require pruning. However, you can keep taller varieties short and bushy by pinching the tops in early June in the North and late June in the South. Remove the top few inches of growth and the aster plant will respond with more side shoots and a bushier plant. Don't pinch the new growth after early July or you'll be removing flower buds for the fall. The shorter, bushier plant may not require staking or caging.
Deadhead (trim) spent flowers in late fall if you don't want your aster plant to self-sow seeds. Asters will spread by seeds and underground rhizomes. Either cut back the whole plant after flowering, since it will be one of the last flowers to bloom in your garden and you'd be cleaning it up soon anyway. Or deadhead the spent flowers on earlier blooming varieties to allow the foliage to naturally yellow and die.
Aromatic Aster is an award-winning native perennial that attracts bees, butterflies, and birds to the garden with a show of purple blooms late summer through fall. The daisy-like flo...Learn MoreAromatic Aster Aromatic Aster Symphyotrichum oblongifoliumAs low as $13.32 Sale $9.99Per Plant - 3" PotAromatic Aster is an award-winning native perennial that attracts bees, butterflies, and birds to the garden with a show of purple blooms late summer through fall. The daisy-like flowers are larger than most Asters, making this a perennial substitute for fall mums. Plant en masse in sunny borders, butterfly gardens, or meadows. The blooms also make long-lasting cut flowers. (Symphyotrichum oblongifolium)
KICKIN® Carmine Red Aster brings vibrant, magenta-red blooms to the fall garden. A profusion of daisy-like flowers covers every inch of this compact, mounding aster for weeks at a t...Learn MoreKICKIN® Carmine Red Aster KICKIN® Carmine Red Aster Symphyotrichum novae-angliae$8.65 Sale $6.49Per Plant - 3" PotKICKIN® Carmine Red Aster brings vibrant, magenta-red blooms to the fall garden. A profusion of daisy-like flowers covers every inch of this compact, mounding aster for weeks at a time, providing a rich source of nectar for pollinators. This low-maintenance marvel maintains a tight, bushy habit without cutting back. (Symphyotrichum novae-angliae)
The violet daisy-shaped blooms of ‚Purple Dome‚ Aster pair beautifully with its honey yellow centers and forest green foliage. This native wildflower is easy to grow and ...Learn MorePurple Dome New England Aster New England Aster Purple Dome Symphyotrichum novae-angliae 'Purple Dome'As low as $6.65 Sale $4.99Per Plant - 3" PotThe violet daisy-shaped blooms of 'Purple Dome' Aster pair beautifully with its honey yellow centers and forest green foliage. This native wildflower is easy to grow and compact, making it a great choice for containers, borders and small-space gardens. 'Purple Dome' bursts into bloom in the late summer, providing much-needed color and vital nectar for pollinators right when much of the garden has finished for the season. (Symphyotrichum novae-angliae)
KICKIN® ‚Lilac Blue‚ Aster is an autumn herald, blooming in late summer with hundreds of pale purple flowers that attract butterflies and bees through fall. This na...Learn MoreKICKIN® Lilac Blue Aster New England Aster KICKIN® Lilac Blue Symphyotrichum novae-angliae KICKIN® Lilac Blue$7.99 Sale $5.99Per Plant - 3" PotKICKIN® 'Lilac Blue' Aster is an autumn herald, blooming in late summer with hundreds of pale purple flowers that attract butterflies and bees through fall. This native cultivar has captured the late season color and pollinator power that we love in full-size Asters in a compact, bushy habit with longer-lasting blooms. KICKIN® 'Lilac Blue' Aster is a long-lived perennial that is deer and rabbit resistant. (Symphyotrichum novae-angliae)
Aster Frikartii Monch is an easy growing nectar plant that adapts well to many growing conditions without complaint. Lavender-blue flowers with daisy-like petals and golden yellow ce...Learn MoreMonch Frikart's Aster Frikart's Aster Monch Aster x frikartii Monch$15.99 Sale $11.99Per Plant - 3" PotAster Frikartii Monch is an easy growing nectar plant that adapts well to many growing conditions without complaint. Lavender-blue flowers with daisy-like petals and golden yellow centers burst into bloom in late June, lasting through September and often until the first frost. Fast-growing, this bushy plant is known for its early blooms, disease-resistant foliage and unusual color. (Aster frikartii)
Aster: End of Season Care
Dividing & Transplanting: The easiest way to propagate asters is to take a division in spring. This will serve a double purpose of creating new plants to share with friends and reducing the size of an overgrown plant. Asters should be divided every 3 to 4 years so they don't get too large. Spring is also the best time to move an existing aster to a new location. In spring, after the ground thaws and plants start to grow, dig up the aster plant and make 6 to 8-inch diameter divisions with a group of leaves and roots. If you want to create just a few divisions, you can separate out pieces from the mother plant along the edge of the root ball, leaving the main plant intact. Replant the division immediately and keep well-watered.
You can also take cuttings of your favorite aster to propagate. In late spring take 2 to 4-inch long cuttings from the stems of the plant. Remove the bottom leaves, dip the cut end in a rooting hormone powder, and stick the cutting in plastic pots filled with loose potting soil. Place the cuttings in bright area out of direct sun and cover the cuttings and pots with a perforated clear plastic bag. Keep watered when dry and they should root within a few months.
You can also collect and save seeds, but it will take a number of years to grow a sizeable, flowering plant.
Cut back aster plants in fall after the foliage yellows to about 2 inches off the ground. Compost the tops.
Pests/ Disease: The biggest pest of asters is powdery mildew disease. This fungal disease causes the leaves to turn white, then yellow and die from midsummer to fall. If severe, it will defoliate the plant and reduce flowering. The best solution to powdery mildew is to grow resistant aster varieties such as 'Winston Churchill' and 'Blue Lake' New York asters, and 'Bluebird' smooth aster. To prevent powdery mildew from getting started, set plants further apart, thin stems from crowded plants in spring and use preventive sprays. Bacillus subtilis is a bacterial spray that fights fungus and works to control mildew before it takes over. You can also use a baking soda solution of 1 tablespoon of baking soda mixed with one gallon of water with a dash of liquid soap. Again, spray early in the season to prevent powdery mildew from taking hold.