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Asters

Eva Monning Eva Monning

What would fall be without a sea of aster flowers? Let us introduce you to this low-maintenance star-shaped flower in all its diversity.

Origin

With over 180 known species, asters are not just part of the largest daisy family but also its namesake (Asteraceae). The precursors to these plants come from America and Africa as well as Europe. These colorful members of the daisy family decorate the garden at the end of the season with flowers that are unusually dense for this time of year without being particularly hard to grow.

Caution: taxonomically, the North American aster species are not strictly asters anymore due to their major genetic differences compared to Eurasian species, so now have their own genus names. This affects the well-known garden varieties of New York aster, New England aster, white heath aster and bushy aster, which now have “Symphyotricum” as their genus rather than “Aster”, as well as the Chinese aster (formerly Aster chinensis, now Callistephus chinensis) and the Goldilocks aster (formerly Aster linosyris, now Galatella linosyris). This distinction is, however, yet to be implemented in the hobbyist and retail spheres. This genus portrait covers all garden varieties traditionally known as asters.

Balcony container

Young New York asters (Symphyotrichum novi-belgii) together with “Tricolor” sage, ivy and a garland of Chinese lanterns look great in a balcony container

Appearance and Growth

Primarily perennials, the sheer variety of aster species means that there is a huge range of sizes, colors and growth patterns. These star-flowered plants can grow to any height from a couple inches to 10 feet tall. The shape, position and foliage also varies drastically from species to species. All asters have one thing in common: their characteristic basket-shaped flowers whereby the long, ligulate, white, pink or blue flowers flowers feature central yellow tubular flowers. They appear individually or grouped at the end of a slightly hairy stem. Asters may be annual or biennial decorative plants, with most varieties forming a rhizome.

Location and Soil

Asters generally value soils with medium nutrient density, and poor locations must therefore be improved with compost. The European Michaelmas-daisy (Aster amellus) and Chinese aster (Callistephus chinensis) prefer limey soil but are satisfied with nutrient-poor sites. European Michaelmas-daisies are suitable for rockeries and can withstand drought well. Most aster species like sun but the large-leaved aster (Aster macrophyllus), Aster ageratoides and white wood aster (Eurybia divaricata) are also suitable for partially shaded sites. Small-growing varieties can be planted as fall-flowering groundcover, even in difficult locations under trees.

Fall asters

Flowering stars in a cottage garden: tall species such as the New England aster and New York aster catch the eye above a wooden fence from afar

Planting and Care

The best times to plant asters are from March to May and from September to November. The European Michaelmas-daisy and Chinese aster should be planted in spring as they will establish better. After establishing, care is limited to pruning in March (simply snap off dry stems), occasional fertilization and moderate watering. Only tall species are fertilized with the addition of compost in spring. Asters should be regularly taken out of the ground, separated and replanted not just for propagation, but also to ensure that the aster flowers over the years.

Pruning

Cut spent stems in spring to around one hand’s width above the ground. Healthy parts of the plant may be added to your compost. If your asters are infected with mildew, any cuttings must be disposed of with general household waste. Bushy aster (Symphyotrichum dumosus) grows runners to form thick bushes. To ensure these don’t remain too compact, cut the plant back by half after flowering and spread mature compost in between. It’s not otherwise necessary to shape asters.

Bouquet

Asters make lovely cut flowers. This posy of New England asters, dahlias, stonecrop and pearly everlasting is a greeting straight from the flower bed

Use

Asters are typical cottage garden plants but also look great in containers or on balconies - but just until spring. Most asters will have reached their maximum height in containers by this point, so should be transferred to a bed. Here, their ideal companions include stonecrop, Japanese anemone, coneflower, dahlia and chrysanthemum. Decorative grasses also look cute. Thanks to their diversity, asters also never look boring when combined with one another. The various shades of red and purple complement each other wonderfully. If you choose the right location and follow a couple of care rules, you will enjoy these intensely colored perennials for many years to come. Plenty of butterflies and bees will also appreciate the flowers in fall for their generous supplies of nectar and pollen.

Lounger in the garden

Fall asters, Japanese anemones, red fountain grass “Rubrum” and fine fall sedges (Carex comans ‘Bronze Form’) make a comfortable lounger a favorite hideaway

Low-growing bushy asters enjoy growing in small groups in the front row, creating a lovely bed border. Tall species can also be planted individually. Their thin stems will, however, need stable support. Caution: some aster varieties tend to lose leaves from the bottom. This can only be partly prevented through regular watering. Dropping leaves is a normal defense mechanism, often seen in times of dryness. It is therefore advisable to plant tall varieties in beds and position smaller but denser plants in front to hide the dry stems.

Species

If you get to know the world of asters, you’ll be surprised at how many species there are with varieties that impress with their flowers in summer and fall. The annual Chinese aster (Callistephus chinensis) grows from 7.87 inches to over 39 inches tall and flowers in white, pink, purple or yellow from July. It loves warm locations in full sun. The Chinese aster’s flowers are mostly double flowers that can reach over 3.94 inches in diameter, making them gorgeous cut flowers.

Chinese asters

Chinese asters have large, mostly double flowers

New England asters, New York asters and bushy asters are the most important groups of September and October bloomers. New England and New York asters (Symphyotrichum novae-angliae and Symphyotrichum novi-belgii) tower above fences and their companions in the flower bed with majestic heights of up to 4 feet. Support the tall stems early on! A well-ventilated location reduces susceptibility to fungal disease. Bushy asters do their name proud, forming a densely flowered carpet up to 20 inches tall around the edges of paths and beds. Shades of blue and purple dominate here. To help you shop: bushy aster varieties “Apollo”, “Blauer Gletscher”, “Herbstgruß vom Bresserhof”, “Niobe”, “Rosenwichtel” and “Zwergenhimmel” have all been considered “excellent” perennials.

New England aster “Andenken an Paul Gerber”

New England aster (Symphyotrichum novae-angliae “Andenken an Paul Gerber”)

The white heath aster (Symphyotrichum ericoides, also known as frost aster) grows as a branching bush that is adorned with countless small flowers in white, pink or delicate purple into November. Important: avoid waterlogging! Alpine asters (Aster alpinus) grow to only 7.87 inches tall. There are ideal for small rockeries. Fall planting will ensure that these plants flower in spring. Despite their similar names, they are not to be confused with the European Michaelmas-daisy (Aster amellus). These like to be occasionally sprinkled with lime, as they tolerate very acidic soil. European Michaelmas-daisies and Chinese asters are among the earliest flowerers, as these compact upright bushes flower from June. European Michaelmas-daisy variety “Veilchenkönigin” is particularly compact with a lovely deep shade of blue-violet. One outlier among the asters is the Goldilocks aster (Galatella linosyris). It is different from its relatives primarily due to its golden-yellow flowers, which it bears from August to September on stalks up to 20 inches tall. The blooms don’t have ligulate flowers, rather just the tubular elements, making them look fluffy. The Goldilocks aster likes sun and is very resilient to even long-lasting drought.

Goldilocks aster (Galatella linosyris)

The flowers of the Goldilocks aster (Galatella linosyris) are significantly different from typical aster flowers

Propagation

Fall asters should ideally be separated in spring. Insert a spade into the ground at an angle and carefully lift the stolon out. Separate out pieces with two to three nodes for new growth. These pieces are replanted in other sunny, nutrient-dense locations. Remove uncontrolled growth beforehand. Place the divided parts as deep in the ground as the parent plant was before. Generous watering supports root establishment in the first few weeks after division.

Separating asters

Even if you don’t want to propagate asters, the rootstock should be regularly separated

Diseases and Pests

If the plant has limp leaves and black shoots, it may have aster yellows and should be removed along with all of its roots. Look for yellow-resistant varieties when making a purchase. Excess fertilization, heat and drought stress encourage mildew. You should therefore carefully choose heat-tolerant varieties for warm, dry locations in the garden. The varieties New England aster (Symphyotrichum novae-angliae), Alpine aster (Aster alpinus) and Aster tongolensis are mildew-resistant. Treating mildew with microfine sulfur is only possible right at the beginning of the infection to prevent spread.

Frequently Asked Questions

What are asters?

Asters are part of the daisy family. There are over 180 types of aster, such as the European Michaelmas-daisy, New York aster and Chinese aster. They originally come from America, Africa and Eurasia. Most species are perennials.

What do asters look like?

Asters can look very different depending on their species and variety. There are small plants that grow to just a couple inches tall as well as large specimens measuring nearly 10 feet tall. All asters have the same typical, basket-shaped flowers. The ligulate flowers arranged around the yellow tubular flowers in the center may be various shades of blue, pink or white depending on the species and variety.

When can asters be planted?

It’s best to plant asters between March and May or between September and November.

When do asters need pruning?

Spent stems can be cut to around one hand’s width above the ground in spring.

Which asters are winter hardy?

Apart from annual Chinese asters, all asters are winter hardy and don’t need any special winter protection.

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