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How to Care for Asters [8 Necessary Green-Thumb Tips]

To properly care for asters, plant them in late spring. Choose a location that receives 6–8 hours of sun each day. Once they’re planted, water your asters once per week to promote vigorous growth. Cut back your asters in June to promote a stronger bloom in late summer and fall, while providing necessary support for taller varieties. Keep on the lookout for powdery mildew and Japanese beetles to prevent your asters from becoming diseased or damaged. Although asters are frost-hardy, provide protection during the winter so your asters can return the following year.

How to care for asters

8 Necessary Tips to Care for Asters

Asters are beloved for their distinctive colorful flowers with bright yellow centers. With proper care, your aster flowers can bloom well into the summer and fall seasons. Here are the best tips to use when caring for asters.

Plant at the Right Time

Plant asters when the ground has thawed and isn’t too damp for digging. Mid-spring to late spring is usually the best time to plant asters. This will ensure a full, beautiful bloom by late summer to early fall.

  • Mid- to late spring is the best time to plant asters.
  • You can begin planting anytime after the last average spring frost.
  • Asters are cold-resistant, so a few cold nights probably won’t harm your plants.

Asters are frost-resistant plants, but newly planted asters are a bit more delicate. So, it’s best to wait until after the danger of frost has passed before planting. However, if there is a late cold snap, your asters should be just fine.

Plant Asters in the Right Location

Plant your asters in an area with well-draining soil that gets 6 to 8 hours of direct sunlight each day. This makes east, south, and west-facing plantings ideal for asters. Because they tolerate heat and cold well, asters can be planted in a variety of locations. Don’t plant your asters in full shade or they won’t grow to their full potential. Similarly, avoid planting asters in a north-facing bed where they won’t get adequate sunlight.

  • Plant your asters in well-draining soil.
  • Provide your asters with full sun.
  • Avoid planting asters in shady locations and north-facing flowerbeds.
  • Different asters varieties grow best in different regions—choose an aster that grows best in your area.

It’s important to plant a species of asters that is compatible with your location. For example, ‘Carmine Red’ asters grow best in Plant Hardiness Zones 5-9, while the New England asters, ‘Purple Dome’ and ‘Pink Crush’ grow best in Zones 3-8.

Provide The Right Amount of Water

Asters require 1 inch (2.5 cm) of water per week. Since asters prefer to be watered once per week at the base of the plant, a soaker hose is a good choice for watering. Simply water for 30–40 minutes with the soaker hose once weekly to keep your asters happy. Continue watering every week until your asters are in full bloom.

  • Give asters 1 inch of water per week.
  • One 30–40 minute watering session with a soaker hose each week is ideal for asters.
  • Do not let the soil get too dry or too wet or your asters may struggle.

Do not let the soil get too dry, or the late summer heat will prevent your asters from blooming. Additionally, overly moist soil can invite unwanted pests and diseases. Although asters don’t require much water, you may need to increase watering frequency during the summer heat. Once the top 2–3 inches (5–7.5 cm) of soil are dry, your asters need more water.

Cut Back Asters at the Right Time

Trim back aster stems to 6 inches tall (15 cm) during the month of June. Choose an area to cut the stem right above a set of leaves. Cutting back your asters will promote stronger growth during their bloom, while also limiting the potential for taller varieties to fall over.

  • June is the best time to cut back asters.
  • Trimming asters in June encourages more flower production.
  • Cut aster stems back until they are 6 inches tall (15 cm).
  • Deadhead asters to prevent mismatched offspring from fallen seeds.

Asters are self-sowing perennials, but their seeds will often not germinate to match the parent flower. If you don’t want mismatching asters, deadhead your asters by pinching back wilted blooms. This will not only prevent baby asters from competing with your established plants, it will also encourage new flower growth.

Provide Necessary Support

Stake taller cultivars of asters, like the New York Aster ‘Harrington’s Pink’ variety. Use these gardening stakes to provide the necessary support for proper growth and prevent toppling. Once you push the stake firmly into the soil, gently tie your asters to the stake with soft cloth or twine.

  • Stake taller aster varieties to prevent them from falling over.
  • Use a soft material such as cloth, flagging tape, or twine to tie asters to stakes.
  • Pinch aster stems to promote taller growth.

You can promote more erect growth of your asters, and possibly eliminate the need for stakes, by pinching the stems early enough in the season. The downside of this is that your asters may bloom later in the season, but it will eliminate the need for tying the stems to stakes.

Divide Every 2 to 3 Years

Asters tend to form large clumps in the center of the plant and need to be divided every 2 to 3 years. Use this sharp gardening spade to dig up and divide larger aster plants in half. A small knife can be used for smaller plants.

  • Divide asters every 2 to 3 years.
  • Early spring or late fall is the best time to divide your asters.
  • Replant divided asters to grow even more flowers in your garden.

If you live in a colder climate area, it’s best to dig up and divide asters in early spring when your asters are just coming out of dormancy. For warmer climates, fall is an ideal time to divide your asters. Cool fall weather will help prevent newly divided asters from drying out after they’re replanted.

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Tackle Common Pests and Diseases

Powdery mildew is a fungal-issue common in aster plants. You will know your aster perennials have powdery mildew if you spot a white powdery substance, similar to flour, covering the leaves of the plant. Use this organic pesticide to treat powdery mildew on your asters. To prevent powdery mildew from returning, allow good air circulation for your plants and maintain healthy soil moisture with a layer of mulch.

  • Use an organic pesticide and proper growing techniques to tackle powdery mildew on your asters.
  • Common aster pests and diseases include aphids, Japanese beetles, lace bugs, and aster wilt.
  • Plant pest and disease-resistant aster cultivars.

Common pests that harm asters include aphids, which cause your flowers to look distorted, Japanese beetles which will leave small holes in the leaves and flowers of your asters, and lace bugs which will leave yellowish-brown spots on the underside of the leaves. Fungal diseases like aster wilt will cause the leaves to turn yellow and blooms to fall from your perennials.

You can also plant aster species that are less susceptible to pests and diseases. A. x frikartii, for example, is a vigorous aster species that resists mildew.

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Protect Asters During the Winter

Some less hardy species of asters require winter protection. During the fall, once your asters are done blooming for the season, cut them back to 6 inches (15 cm) above the ground. Then, use mulch, such as straw or evergreen branches, to cover the flowers to protect them during the winter months ahead.

  • Cut asters down to 6 inches (15 cm) tall once the blooming season ends.
  • Spread a 3–4-inch (7.5–10 cm) deep layer of mulch on the soil around your asters.
  • Trimming and mulching your asters helps prevent frost and ice damage during winter.

Asters are frost-resistant perennials, but proper winter protection helps prevent frozen, cracked ground that can damage the roots of all aster varieties. A layer of mulch is a must for less cold-tolerant varieties, but will benefit any type of aster you plant.

Caring for Asters

To properly care for asters, do the following:

  • Plant asters at the right time of the year.
  • Plant aster perennials in well-draining garden beds that receive full sun.
  • Provide 1 inch (2.5 cm) of water per week to your asters.
  • Cut asters back to 6 inches (15 cm) during the month of June.
  • Stake taller aster varieties to prevent them from falling over.
  • Divide asters once they begin to clump in the center, usually every 2–3 years.
  • Use an organic pesticide to tackle common aster issues like powdery mildew.
  • Lay down a layer of mulch in the fall to insulate your asters’ roots for the winter ahead.

By following these tips, you can ensure your asters bloom beautifully for your enjoyment. Choosing the right planting location, providing weekly water, and protecting your aster from cold ensure healthy plants that produce more flowers and are less likely to be attacked by disease.

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