Asters are a beautiful addition to any garden, providing vibrant colors and attracting pollinators such as bees and butterflies. Growing these flowers successfully involves understanding their specific needs and providing the right conditions for them to thrive. This guide will take you through the essential steps to grow aster flowers, from selecting the right variety to maintaining their health throughout the growing season.
Understanding Aster Flowers
Asters belong to the Asteraceae family, which includes daisies and sunflowers. They are perennial plants, meaning they come back year after year, with some varieties that are annuals. Asters are known for their star-shaped flower heads, which come in a range of colors, including purple, pink, blue, white, and red. They bloom in late summer to fall, providing much-needed color in the garden when many other flowers have faded.
Selecting the Right Variety
Choosing the right variety of aster is crucial for successful growth. There are many types of asters, each with its unique characteristics. Some popular varieties include:
New England Aster (Symphyotrichum novae-angliae): This variety is known for its tall growth and vibrant purple flowers. It can grow up to six feet tall and is hardy in USDA zones 4-8.
New York Aster (Symphyotrichum novi-belgii): Slightly shorter than the New England aster, this variety also comes in various colors and is hardy in USDA zones 4-8.
Wood’s Aster (Symphyotrichum dumosum): A compact variety that grows about 12-18 inches tall, making it perfect for borders and containers. It is hardy in USDA zones 4-8.
Smooth Aster (Symphyotrichum laeve): Known for its smooth leaves and purple-blue flowers, this variety is hardy in USDA zones 4-8 and grows up to three feet tall.
Choose a variety that suits your garden’s size and climate. Consider the mature height of the plant and the color that will best complement your garden’s design.
Preparing the Soil
Asters prefer well-drained soil with a pH level between 5.8 and 6.5. Before planting, test your soil to determine its pH and nutrient levels. If necessary, amend the soil to meet the needs of the asters. Adding organic matter, such as compost or aged manure, can improve soil structure and fertility.
For optimal drainage, consider planting asters in raised beds or mounds. This is especially important if you have heavy clay soil, which can retain too much moisture and cause root rot.
Planting Aster Flowers
Timing
The best time to plant asters is in the spring, after the last frost has passed. This gives the plants enough time to establish their roots before the hot summer weather.
Spacing
Asters need adequate space to grow and spread. Plant them about 1 to 3 feet apart, depending on the variety’s mature size. Proper spacing ensures good air circulation, which helps prevent fungal diseases.
Planting Steps
Digging the Hole: Dig a hole that is twice as wide and just as deep as the root ball of the plant.
Amending the Soil: Mix some compost or other organic matter into the soil that will go back into the hole.
Planting: Place the aster plant in the hole, ensuring the top of the root ball is level with the surrounding soil. Backfill with the amended soil, gently pressing down to remove air pockets.
Watering: Water the newly planted asters thoroughly to settle the soil around the roots.
Watering and Mulching
Asters need consistent moisture, especially during the growing season. Water them deeply once a week, providing about 1 inch of water. During hot, dry periods, you may need to water more frequently.
Mulching helps retain soil moisture and keeps the roots cool. Apply a 2-3 inch layer of organic mulch, such as shredded bark or straw, around the base of the plants. Be sure to keep the mulch a few inches away from the stems to prevent rot.
Fertilizing Asters
Asters benefit from regular feeding, especially during the growing season. Use a balanced, slow-release fertilizer with an N-P-K ratio of 10-10-10 or 5-10-5. Apply the fertilizer in early spring when new growth begins and again in mid-summer.
Avoid over-fertilizing, as this can lead to excessive foliage growth at the expense of flowers. Follow the manufacturer’s instructions for the correct application rate.
Pruning and Deadheading
Pruning helps maintain the shape and health of aster plants. In late spring or early summer, pinch back the stems by one-third to encourage bushier growth and more blooms. This is especially important for tall varieties that can become leggy.
Deadheading, or removing spent flowers, promotes continuous blooming. Regularly check your plants and snip off faded flowers just above a set of healthy leaves.
Supporting Tall Varieties
Tall aster varieties, such as the New England aster, may need support to prevent them from flopping over. Use stakes, cages, or plant supports to keep the stems upright. Install supports early in the season to avoid damaging the roots later on.
Managing Pests and Diseases
Asters are relatively resistant to pests and diseases, but they can occasionally be affected by:
Aphids: These small, sap-sucking insects can cause distorted growth and yellowing leaves. Control them with insecticidal soap or by introducing natural predators like ladybugs.
Powdery Mildew: This fungal disease appears as a white, powdery coating on the leaves. Prevent it by ensuring good air circulation and avoiding overhead watering. Treat affected plants with a fungicide if necessary.
Leaf Spot: Fungal or bacterial leaf spots can cause brown or black spots on the leaves. Remove and destroy infected leaves, and apply a fungicide if needed.
Regularly inspect your plants for signs of pests and diseases. Early detection and treatment can prevent widespread damage.
Overwintering Asters
In regions with cold winters, asters may need some protection to survive. Cut back the plants to about 2-3 inches above the ground after the first frost. Apply a thick layer of mulch, such as straw or leaves, to insulate the roots and protect them from freezing temperatures.
In milder climates, asters can remain evergreen. However, they may still benefit from a light layer of mulch to retain soil moisture and suppress weeds.
Propagating Asters
Asters can be propagated by division or from seeds.
Division
Divide established aster plants every 3-4 years to rejuvenate them and prevent overcrowding. The best time to divide asters is in early spring before new growth begins.
Digging Up the Plant: Carefully dig up the entire plant, ensuring you get as much of the root system as possible.
Dividing the Clump: Use a sharp knife or spade to divide the root ball into smaller sections, each with at least one healthy shoot and a portion of the root system.
Replanting: Plant the divisions in prepared soil, spacing them appropriately. Water thoroughly to help them settle in.
See Also: Caring for Primroses After Flowering
Seeds
Growing asters from seeds is a cost-effective way to propagate them, but it requires more time and patience.
Sowing Indoors: Start seeds indoors about 6-8 weeks before the last expected frost. Sow the seeds in seed trays or pots filled with a seed-starting mix. Cover them lightly with soil and keep them moist.
Germination: Place the trays in a warm, bright location with temperatures between 65-75°F (18-24°C). Seeds should germinate in 14-21 days.
Transplanting: Once the seedlings have developed two sets of true leaves, transplant them into individual pots. Harden them off by gradually exposing them to outdoor conditions before planting them in the garden.
Companion Planting with Asters
Asters make excellent companion plants in the garden. Their late-season blooms provide nectar for pollinators, which can benefit nearby plants. Some good companions for asters include:
- Coneflowers (Echinacea): Their similar growing conditions and complementary colors make them great partners for asters.
- Goldenrod (Solidago): These plants bloom around the same time as asters, creating a beautiful contrast of colors.
- Sedum: The low-growing, succulent nature of sedum makes it a good ground cover around taller aster varieties.
- Ornamental Grasses: Grasses add texture and movement to the garden and look stunning when paired with asters.
Avoid planting asters near plants that are prone to similar diseases, such as powdery mildew.
Conclusion
Growing aster flowers can be a rewarding experience, bringing vibrant colors and pollinators to your garden. By selecting the right variety, preparing the soil, planting correctly, and providing proper care, you can enjoy these beautiful flowers year after year. With regular watering, feeding, pruning, and protection from pests and diseases, your asters will thrive and become a highlight of your garden. Whether you are a seasoned gardener or a beginner, following these guidelines will help you successfully grow and enjoy aster flowers.
