Asters : to grow, to cultivate and to maintain

Botany

The Asters comprise nearly 250 species, mainly perennials, but also annuals or biennials. There are even some shrubs. They mainly originate from North America. A few species are native to Asia and Europe. In France, one can mainly find Aster amellus, Aster tripolium, Aster pyrenaeus, Aster linosyris (now called Galatella linosyris), as well as Aster alpinus in mountainous regions. Some are protected! The most commonly cultivated Asters are Aster novae-angliae and Aster novi-belgii, two closely related species that are difficult to differentiate. They are quite hardy plants: they can withstand at least down to -20 °C!

Aster novae-angliae: botanical illustration

They belong to the Asteraceae family. With over 20,000 species, it is one of the largest families in the vegetable kingdom. It includes many plants commonly grown in gardens, such as daisies, marigolds, or dahlias, as well as daisies. It also includes plants consumed as vegetables like artichokes or lettuce.

The name Aster comes from Greek and means Star, referring to the shape of the flowers. Due to recent changes in botanical nomenclature, many asters have changed names to now be called Symphyotrichum or Eurybia. This is particularly true for the “asters” from North America. Thus, Aster nova-angliae has become Symphyotrichum nova-angliae, Aster novi-belgii is now Symphyotrichum novi-belgii, and Aster dumosus is called Symphyotricum dumosum, to name just a few. The Aster macrophyllus has become Eurybia macrophylla and the Aster divaricatus is now Eurybia divaricata. Although most nurserymen continue to sell these asters under the old names, do not be surprised to see these curious genus names appearing on labels.

Asters can grow in a erect clump or have a more spreading habit. Their height varies greatly. Some exceed 1 meter in height. The Asters novae-angliae are among the tallest (up to 1.50 m for the variety ‘Violetta’). Others form small cushions, not exceeding 30 cm in height, like Aster dumosus ‘Marjorie’. There is even one climbing species: Aster carolinianus! Asters often have ramified stems that are very robust, sometimes almost woody.

Asters generally bloom in autumn, but there are also varieties with spring flowering (like Aster alpinus) or summer flowering (like Aster sibiricus). Their flowering is very colourful and abundant! They offer a superb palette of blue, mauve, and pink. Light and airy, it provides a “cloud-like” effect similar to that of gypsophila! This is particularly true for Aster ‘Monte Cassino’, which has a multitude of small white flowers.

The flowers are arranged in heads, measuring between 1 and 8 cm in diameter, and resemble daisy or marguerite flowers. What one thinks is a single flower is actually a multitude of tiny flowers grouped together, of two types: yellow tubular flowers in the centre, and ligulate flowers (composed of a long coloured petal) on the outside. The colours vary between pink, purple, blue, and white, with petals gathered around a yellow centre. Some Asters offer a striking pink flowering!

The flowering can be single or double. Thus, depending on the varieties, the petals (or rather, the ligulate flowers located on the outside of the head) are more or less numerous. There are several rows in Aster dumosus ‘Starlight’, giving it a rather sophisticated look, while Aster cordifolius ‘Ideal’ has far fewer. Some varieties do not have ligulate flowers: this is precisely what gives such a different appearance to the yellow flowers of Aster linosyris.

Used as cut flowers, asters bring lightness to bouquets. They last at least a week in a vase. They are also good melliferous plants, their flowers attract many insects and butterflies.

Asters have simple and fairly thin leaves, except for those of Aster macrophyllus and cordifolius, which are broad and heart-shaped. The leaves are deciduous and arranged alternately on the stem. They are generally green, but can also take on very dark shades, for example, purples in Aster laterifolius ‘Lady in Black’.

Asters possess rhizomes through which they can spread widely. Some can even naturalise!

After flowering, asters bear decorative fruits, composed of an achene topped with an egret of bristles, which allows them to fly away with the wind like dandelion flowers! They have a very light and delicate appearance.

The seeds of Asters are topped with an egret that allows them to fly away, to be dispersed by the wind. (here, Aster subulatus – photo Harry Rose)

The botanical species:

• Symphyotrichum novi-belgii or Aster novi-belgii

These are the most common asters in gardens. They bloom in autumn, a little earlier than Asters novae angliae. They are also more susceptible to diseases, particularly powdery mildew.

• Symphyotrichum novae-angliae or Aster novae-angliae

Commonly cultivated, these asters offer autumn flowering, often purple. They have the advantage of being quite resistant to diseases. They often exceed 1 meter in height. Their flowering is a bit denser than that of Asters novi-belgii.

• Aster amellus

This is a medium-sized aster, with summer flowering in blue – violet. It is protected in France. It is also called “Christ’s Eye”.

• Symphyotrichum dumosum or Aster dumosus

Native to North America, this Aster offers blue – mauve flowering in summer. It is quite compact and forms cushions. It adapts well to pot culture! Discover the variety ‘Jenny’, with pink flowers.

• Aster alpinus

The Alpine Aster has the particularity of blooming in spring. With its spreading and fairly low habit, it is a good rock garden plant. It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

Discover asters in video with Olivier:

The main varieties of Asters

The Most Popular Varieties

Our Favourite Varieties

Other Varieties to Discover

Aster lateriflorus Lady In Black

This aster is covered in autumn with numerous small white and pink flowers, highlighted by very dark, purplish foliage. It is a fairly tall variety. Easy to grow, it enjoys full sun but also tolerates light shade.

• Flowering time October, November
• Height at maturity 1,20 m

See the product sheet

Aster cordifolius Ideal

This is a tall variety that bears countless small pale blue flowers. A spectacular and very airy flowering that changes colour: the yellow centre of the flowers turns pink or red over time. Its very light and airy aspect gives it a 'cloud' appearance.

• Flowering time October to December
• Height at maturity 90 cm

See the product sheet

Aster pringlei Monte Cassino

A fairly tall plant, whose particularly light flowering creates a vapour-like effect similar to that of gypsophila. It bears a multitude of small white flowers and very fine leaves. It enjoys direct sunlight and is very drought-resistant. It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Flowering time September to December
• Height at maturity 90 cm

See the product sheet

Aster novae-angliae Septemberrubin

This variety has a much brighter flowering, with petals of a bright pink-red arranged around a yellow centre. It is a tall variety, also known as 'September Ruby'. It is susceptible to powdery mildew but tolerates dry soils quite well. Enjoy its colourful flowering to create bouquets!

• Flowering time September, October
• Height at maturity 1,20 m

See the product sheet

Aster dumosus Jenny

Aster 'Jenny' is a fairly compact variety, appreciated for its bright pink flowering! It prefers relatively cool and rich soils. You can place it at the front of a border or grow it in a container.

• Flowering time September to November
• Height at maturity 35 cm

See the product sheet

Aster novae-angliae Herbstschnee

This aster bears large pure white flowers with a yellow centre, resembling daisies. It is robust and resistant to powdery mildew. It is a tall variety that will add volume to a border.

• Flowering time September to December
• Height at maturity 1,20 m

See the product sheet

Aster dumosus Lady in Blue

'Lady In Blue' is a small aster with a compact habit, ideal for flowering a border or the front of your beds. It has an abundant flowering of a soft blue.

• Flowering time October, November
• Height at maturity 25 cm

See the product sheet

Aster novae-angliae Andenken an Alma Pötschke

This is a tall variety that offers a generous pink-red flowering with a yellow centre from the end of summer. It is a robust plant, not very susceptible to diseases. It will bring a lot of colour to your borders!

• Flowering time October, November
• Height at maturity 1,20 m

See the product sheet

Aster cordifolius Little Carlow

Aster 'Little Carlow' is a tall variety that is covered in early autumn with countless small mauve-blue flowers. It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS). It is appreciated for its abundant and delicate flowering.

• Flowering time October, November
• Height at maturity 90 cm

See the product sheet

Aster frikartii Mönch

This is a medium-sized variety with a long summer flowering period. It has large soft blue flowers and dark green foliage. It is quite resistant to diseases. It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Flowering time August to November
• Height at maturity 70 cm

See the product sheet

Aster novi-belgii Marie Ballard

This tall variety bears beautiful soft blue flowers in autumn. It is appreciated for its delicate hue and double flowering, where the numerous petals conceal the yellow centre of the flower. It is running.

• Flowering time October, November
• Height at maturity 1 m

See the product sheet

Aster amellus Veilchenkönigin - Violet Queen

A compact variety with a long flowering period. It is covered from mid-summer with multiple purple flowers shaded by a yellow centre. It is easy to grow and has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Flowering time August to December
• Height at maturity 50 cm

See the product sheet

Aster linosyris

A surprising aster that offers a beautiful yellow summer flowering, without ligulate flowers. It is quite compact and will bring brightness to your borders. It grows spontaneously in France. It has recently changed its name to Galatella linosyris.

• Flowering time September, October
• Height at maturity 60 cm

See the product sheet

Aster novi-belgii Fellowship

This variety has large double flowers, soft pink. The delicate colour of its numerous petals allows it to be easily integrated into a romantic border. It has been awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Flowering time September to November
• Height at maturity 1,20 m

See the product sheet

Aster novae-angliae Ann Leys

An amazing variety that looks like no other! It bears dark purple flowers in autumn, surrounded by numerous green bracts. It is a good variety for creating bouquets. Enjoy its purple hue to add depth to your borders and contrast with brighter flowers!

• Flowering time October to December
• Height at maturity 65 cm

See the product sheet

Aster novae-angliae Purple Dome

Aster 'Purple Dome' is a dwarf variety, very bushy. From September, it is covered with purple flowers shaded by a yellow centre. It is resistant to powdery mildew and adapts well to pot culture.

• Flowering time October, November
• Height at maturity 1 m

See the product sheet

Aster divaricatus

This is a rather low aster that offers numerous small white flowers with a yellow-brown centre at the end of summer, borne on black stems. The flowers have relatively few petals compared to other varieties. Suitable for shady situations, it will thrive if you place it in woodland. It is appreciated for its natural and wild aspect!

• Flowering time October to December
• Height at maturity 50 cm

See the product sheet

Aster diplostephioides

This aster, native to Asia, surprises us with its flowers that are very different from other varieties! It has numerous really fine pale mauve petals gathered around a large yellow and black centre. It will thrive in rockeries.

• Flowering time July to September
• Height at maturity 30 cm

See the product sheet

Planting asters

Where to plant?

Plant your asters preferably in full sun! Some varieties appreciate a slightly shaded position. The species best suited for shade is Aster divaricatus (or Eurybia divaricata): feel free to install it in woodland areas. Most will thrive in well-drained soil that remains cool in summer. They do not like excess moisture in winter, as waterlogged soil could cause the roots to rot. If your soil is heavy, add compost to lighten it and enrich it.

Some prefer well-drained, rather dry, and sunny soils. This is generally the case for compact varieties that thrive in rock gardens. The most suitable for this use are Aster amellus, Aster alpinus, and Aster tongolensis. Conversely, other varieties prefer rich and cool soils, in partial shade. For instance, the New England aster (Aster novae-angliae) enjoys cool, even moist soils. Avoid overly sandy soils, which dry out quickly. They appreciate soils that are fairly rich in humus. This is why we recommend adding organic matter. Generally, asters tolerate calcareous soils quite well.

Install the taller varieties, such as Aster tataricus ‘Jindai’, at the back of the border, while the smaller ones, like Aster ‘Wartburgstern’ or the Asters dumosus (or Symphyotrichum dumosum) are perfect for adding colour to the front of a border or a bed!

If you wish to grow them in pots, choose the more compact varieties. The Aster dumosus is particularly suitable! Discover the variety ‘Jenny’ with bright pink flowers. Asters planted in containers will require more regular watering than those in the ground.

Aster divaricatus will appreciate being planted in woodland, Aster novi-belgii ‘Lady in Blue’ will thrive in borders, while Aster alpinus is more suited for rock garden planting.

When to plant?

We recommend planting asters in autumn, although it is also possible to do so in spring.

How to plant asters?

1. Moisten the root ball by placing it in a basin filled with water.
2. Dig a planting hole that is deep enough, two to three times the size of the root ball.
3. Add compost to enrich the soil.
4. Place your aster, fill in around the root ball, and then gently firm it down.
5. Stake the taller varieties.
6. Water generously.
7. Apply a mulch to keep the soil cool and limit weed growth.

Continue to water during the first few weeks, and as needed throughout the summer.

The planting distance can vary quite a bit: about twenty centimetres for the more compact varieties (e.g. Aster dumosus) to 40 or 50 cm for the taller ones. By maintaining a sufficient planting distance, you will achieve more vigorous plants that are less susceptible to diseases, as good air circulation limits their occurrence.

→ Learn more in our advice sheet: Growing an Aster in a pot

Maintenance

Easy to grow, asters are plants that require very little maintenance. It is advisable to stake the tallest varieties, such as Aster cordifolius and Aster novae-angliae, to prevent them from falling over in the wind or rain. Also, add a bit of compost each year at the beginning of spring. We suggest mulching, especially for summer, to keep the soil cool. Some watering will be necessary during summer droughts. When watering, direct the stream towards the base of the plant, avoiding splashing the foliage, which could encourage the onset of diseases (powdery mildew). If you are growing them in pots, water regularly, as the substrate dries out faster than in the ground, and provide liquid fertiliser during the summer. It is important to divide the asters at least every four years to rejuvenate and aerate the clumps. You can remove faded flowers as they appear to prolong flowering and prevent your asters from self-seeding.

Asters are quite sensitive to powdery mildew, especially Aster novi-belgii (Symphyotrichum novi-belgii). We recommend carrying out a preventive treatment during the summer, for example with sulphur or horsetail manure. This disease is favoured by dense planting, a confined situation (air circulation is essential), and shade. To avoid it, plant your asters in full sun and keep the soil cool during the summer. Also, favour Aster novae-angliae, as they are much less sensitive.

Asters can sometimes be affected by rust, which manifests as discoloured spots on the leaves and rust-coloured pustules on their undersides. They are also susceptible to downy mildew. Humidity promotes these diseases, and to remedy this, Bordeaux mixture and horsetail manure are quite effective. We also suggest removing damaged parts to limit their spread. In general, to protect your asters from diseases, place them in well-draining soil, avoid planting them too densely, and refrain from watering the foliage. Waterlogged soil makes them more susceptible to diseases.

Slugs and snails enjoy nibbling on young aster leaves. As a preventive measure, you can place wood ash or sawdust around them to create a barrier. Occasionally, aphids also attack asters.

We recommend pruning asters in June by pinching the tips (Chelsea chop). Shorten the stems by half using pruning shears. This encourages better flowering, a bushier and more compact habit, while allowing good air circulation, thus limiting the risk of diseases (powdery mildew). Similarly, at the beginning of winter, when the stems have dried, it is best to cut them back to ground level. If you live in a region with a harsh climate, wait until the end of winter, as the stems will protect the plant from the cold.

Tall asters often require staking; discover our video on how to stake asters easily.

Aster x frikartii ‘Mönch’ (photo Dominicus Johannes Bergsma)

Multiplication

Asters multiply quite easily. However, we recommend doing so by division, a technique that will ensure you quickly obtain new plants identical to the original variety, unlike sowing.

Division of clumps

Division is the best technique for multiplying asters. Do it every three years for Asters dumosus, novi-belgii, novae-angliae, and x frikartii. Preferably intervene in spring, around April, although division is also possible in autumn.

Dividing asters allows you to renew the clumps and make them more vigorous. This will help you control their spread, preventing them from overtaking the space at the expense of other plants. Additionally, it aerates the clumps and prevents the appearance of powdery mildew by allowing better air circulation.

Identify the Asters to divide, then cut the dry stems at ground level. Dig up the clump with a spade. Then divide the stump into several pieces, ensuring each has enough roots and several young shoots. Replant and then water generously. We recommend installing a mulch to keep the soil cool.

Discover our video tips – Dividing an Aster:

Propagation by cuttings

You can propagate the stems of asters in spring.

1. Start by preparing a pot by filling it with a mixture of potting soil and sand.
2. Take a cutting of stem, about 10 centimetres long. Cut it at the base just below a node (the point where leaves attach to the stem).
3. Prepare the cutting by removing the leaves at the base. Leave just a few leaves at the top of the stem.
4. Make a hole in the substrate with a thin stick or pencil.
5. Place the cutting in the hole, then firm the soil around the stem to ensure good contact between the plant and the substrate and avoid air pockets.
6. Water
7. Place the pots in a bright location, out of direct sunlight.

Ensure the substrate remains moist, but not overly wet, while the cutting roots. Wait until autumn to plant the young plants in the ground.

Sowing

Many varieties of asters self-seed spontaneously, to the point of becoming almost invasive. You will quickly obtain a large number of plants, but you can easily remove them by pulling them out.

Sow your asters in spring, either directly in the ground or under cover to plant them in their final location in autumn. Hybrids are sterile.

Prepare pots by filling them with potting soil and gently firming. Then sow the seeds and cover with a thin layer of potting soil. Water and place the pots in a sheltered location. The substrate should remain moist until germination, which will occur in one to two weeks. In autumn, you can plant your seedlings in the ground.

→ Learn more about the propagation of asters with Ingrid’s tips in our tutorial.

Pairing asters

With their airy habit and delicate, light flowering, asters complement grasses beautifully (for example, stipa, miscanthus, or pennisetum). The tallest varieties create a lovely wild meadow effect.

A beautiful association with grasses! Aster ‘Sonora’ with Calamagrostis ‘Karl Foerster’, Aconitum carmichaelii ‘Arendsii’, Kniphofia, and Miscanthus. (copyright MAP – Clive Nicholspettifers Garden Oxfordshire)

Astors easily fit into the composition of colourful mixed borders, alongside other perennials and bushes. The shorter varieties can animate the front of the beds, while the taller ones will add volume at the back. At the edge, you can use Aster lateriflorus ‘Horizontalis’, which forms a low, spreading tuft that is covered in small white and purple flowers in autumn. Plant them alongside grasses, hardy geraniums, or achilleas.

Asters brighten up autumn with their colourful flowering! Take the opportunity to create a stunning autumn scene in warm tones, with shades ranging from purple, pink, orange, to red. Integrate into this type of bed grasses, echinaceas, a few clumps of Sedum spectabile, or Buenos Aires verbena.

Asters are perfect for creating an autumn bed! Echinacea pallida (photo credit GAP Jo Whitworth), Echinacea purpurea ‘Magnus’ (photo Peter Rosbjerg), Sedum ‘Herbstfreude’, and Verbena bonariensis.

Some asters will thrive in rockeries. This is the case for Asters alpinus and amellus, which are suited to dry, sunny situations. You can associate them with sedums, houseleeks, or small grasses like Stipa tenuifolia. Conversely, Aster divaricatus will appreciate if you install it in woodland, where it will accompany ferns and hostas.

For more inspiration, check out our advice sheet: “10 ideas for associating Asters”