Asters are a popular choice for gardeners seeking to extend vibrant color into the late growing season. These daisy-like flowers offer a beautiful display when many other blooms begin to fade.
Understanding Aster Varieties
The Aster genus encompasses diverse species in size, color, and bloom time. Two prominent types are the New England aster (Symphyotrichum novae-angliae) and the New York aster (Symphyotrichum novi-belgii), both native to North America.
New England asters typically grow thicker stems with hairy leaves, reaching 3 to 4 feet, and produce full, dense flowers in late summer or early fall. New York asters can also grow 2 to over 4 feet tall, but generally possess thinner, smoother stems.
Beyond these common types, other varieties include the bushy blue wood aster (Symphyotrichum cordifolium) with small blue-to-white flowers, and the low-growing heath aster (Symphyotrichum ericoides) which forms a ground cover with small white blooms. Flower colors span a spectrum from white, pink, and red to various shades of purple and blue, ensuring a suitable option for almost any garden. Annual asters, like China aster, provide summer bedding and cut flowers.
Planting Asters
Planting asters begins with proper site selection and soil preparation. Most asters thrive in full sun, promoting robust flowering. While some tolerate partial shade, shadier conditions result in fewer blooms and lankier growth.
Asters prefer moist, well-draining, loamy soil, ideally with a neutral to slightly acidic pH. Heavy clay soils can lead to root rot, while overly dry, sandy soils cause wilting. Before planting, enrich the soil with 2 to 3 inches of compost or other organic matter to improve drainage and fertility.
Plant young asters outdoors in mid to late spring after the last frost, allowing establishment before flowering. Mature, potted asters can also be planted in late summer or early fall. Space young plants 1 to 3 feet apart, depending on mature size, to ensure adequate air circulation.
Sow seeds about 1 inch deep in pots or flats. For bare roots, loosen the soil about a foot deep and plant them at their previous growing depth.
Ongoing Aster Care
Ongoing care ensures aster health and vigorous blooming. Established plants generally require regular watering, particularly during dry periods, to keep the soil consistently moist but not waterlogged. Improper watering can cause foliage drop or inhibit flowering.
While asters are not heavy feeders, a spring application of compost or a balanced granular fertilizer, such as a 10-10-10 formula, can support growth. For lighter, sandy soils, a general-purpose fertilizer in spring can be beneficial. Container-grown asters may benefit from liquid feeds.
Cease fertilization once blooms begin to open, typically by August, as excessive nutrients can shorten the blooming period. Deadheading spent blooms can encourage continuous flowering, though it is not always necessary.
Taller aster varieties may require staking to prevent flopping, especially if over 3 to 4 feet. Place supports before mid-summer. Pinching back plants by one-third in early summer (the “Chelsea chop”) promotes bushier growth and reduces the need for staking. Divide aster clumps every three to five years in early spring to maintain vigor and health, preventing woody, sparse centers.
Troubleshooting Common Aster Problems
Asters are generally robust plants, but they can occasionally encounter issues with pests and diseases. Powdery mildew, a common fungal disease, appears as white patches on leaves, especially in humid conditions or with poor air circulation. Manage by ensuring proper plant spacing and avoiding overhead watering.
Rust is another fungal problem, causing orange pustules on leaf undersides. Remove affected foliage and maintain good air circulation.
Insect pests like aphids and lace bugs can affect asters. Aphids are small, found on stems and leaf undersides, and can be treated with insecticidal soap.
Lace bugs feed on plant juices, causing yellowing foliage and leaf drop. Apply insecticidal soap, coating all sides of the foliage, to address infestations.
Yellowing leaves or stunted growth, especially with distorted flowers, might indicate aster yellows, a bacterial disease spread by leafhoppers. Unfortunately, there is no cure; remove and destroy infected plants to prevent spread.