Michaelmas daisies: plant care & the most beautiful autumn asters

Looking for an insect-friendly plant that blooms in autumn? Then the Michaelmas daisy is just the flower for you. It comes in a variety of colours and starts showcasing its beauty in the last days of summer, ushering in the autumn.

There is still plenty of garden work to be done in autumn. Michaelmas daisies, also known as autumn asters (Symphyotrichum and Aster), come in many different colours and are an excellent example of late season flowers. Read on to find out what to bear in mind when planting and caring for your own Michaelmas daisy.

Did you know? While some asters are still part of the Aster genus, many Michaelmas daisies that used to belong to the Aster group are now classified as Symphyotrichum.

Michaelmas daisies: origin and properties

Asters from the genus Symphyotrichum originate from North America and Canada. Those of the genus Aster, on the other hand, are native to Eurasia. Plants of both genera have long been found in local gardens and their late summer flowers provide lovely pops of colour.

Autumn asters are hardy perennials that really stand out in the garden. They grow to a height of 20 to 140 cm and a width of 30 to 90 cm, depending on the species. The leaves can be elliptical, lanceolate and either smooth or rough. The colour of the ray-shaped flowers can vary from white to light pink to violet, again depending on the species and variety. The yellow stamens attract a multitude of insects. A garden full of autumn asters is truly a haven for bees, bumblebees and other pollinators, as they are rich in nectar, especially the native European Michaelmas daisy.

When do Michaelmas daisies flower? Autumn asters flower from the beginning of September into November.

Tip: People sometimes confuse asters and chrysanthemums (Chrysanthemum) because they look very similar. While both genera belong to the daisy family known as Asteraceae, the most notable difference between autumn asters and chrysanthemums is that the latter are usually not winter hardy.

Autumn aster varieties

There are many types of autumn asters with varying flower colours. Here are a few of our favourites:

Rice button aster (Symphyotrichum dumosum)

The rice button aster grows like a cushion. Due to its stocky growth habit, this aster only grows to a maximum height of 20 to 40 cm. Depending on the variety, the flowers vary from pink to purple. You can create a lovely sea of flowers by planting ten to twelve rice button aster plants over one square metre, keeping a planting distance of 30 cm between each of them.

White heath aster (Symphyotrichum ericoides)

The white heath aster has a bushy habit with upright stems and grows to a height of 50 to 100 cm. The flowers are small and, as the name suggests, white. These asters have a growth width of 45 to 50 cm, so you can plant around four to six white heath asters per square metre, keeping a planting distance of 45 cm between each plant.

New York aster (Symphyotrichum novi belgii)

This Michaelmas daisy flowers blue-violet. It reaches a maximum height of 70 to 140 cm. New York asters have a bushy growth habit and form short runners. In contrast to the other species mentioned here, this one requires soil that is a little more moist. New York asters grow to about 70 to 80 cm wide, so you should only plant one to three plants per square metre, keeping a planting distance of 80 cm.

New England aster (Symphyotrichum novae angliae)

This Michaelmas daisy cultivar grows in dense clumps and reaches a height of 50 to 100 cm. It blooms mainly in shades of pink and, at around 10 cm in size, the flowers are quite large. The leaves feel velvety to the touch as they are covered in fine hairs. As this species is rather wide, measuring up to 90 cm across, you will need to plant them about the same width apart.

European Michaelmas daisy (Aster amellus)

This bee-friendly aster has a bushy growth habit and can reach a height of between 30 and 60 cm. The flowers are pink to blue-violet and small. Due to its maximum growth width of 40 to 50 cm, this species’ planting distance is about 45 cm, which amounts to about four to six plants per square metre.

Rough-surface aster (Aster ageratoides)

This is a very drought-resistant species of aster that grows broad and tall, reaching between 70 and 100 cm high. The flowers are mostly light purple and small, while the leaves are lanceolate and rough. When planting this aster, keep a planting distance of about 60 cm, or two plants per square metre.

Planting Michaelmas daisies: where, when and how

Michaelmas daisies like it sunny. With too much shade, the number of flowers will diminish. Additionally, the soil must be rich in minerals and nutrients, well-drained, and dry to fresh. Autumn asters do not tolerate excessively moist soil. If your soil is rich in clay, mix in some sand. Soil that is too sandy, on the other hand, needs to be amended with compost. Our peat-free Plantura Organic Enriched Compost is ideal for this. Thanks to its high humus content, it helps promote a healthy soil life and provides plenty of beneficial nutrients. This in turn ensures sustainably beautiful, lush plants. This soil is also recommended for potted plants.

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When to plant autumn asters? You can buy autumn asters in containers and plant them out on frost-free days anytime between spring and autumn. Propagated asters are typically sold just before they flower in late summer and should be planted out straight away.

Tip: Ornamental grasses, delphinium and phlox make good autumn aster companion plants in perennial beds.

Michaelmas daisies in pots and on balconies

Some varieties, especially the larger ones, do not grow well in pots. But compact cultivars like the rice button aster do well on the balcony. When planting two or more rice button asters together, remember to keep a planting distance of about 10 cm. Place your potted aster in a spot protected from rain to reduce the risk of infection by powdery mildew. It is also important to add a drainage layer in the pot to stop the soil from staying too moist for too long.

Michaelmas daisy care

Michaelmas daisies are undemanding, easy-care plants. That said, there are a few things you should know when it comes to caring for your autumn asters.

Pruning, watering and fertilising

Cut autumn asters back to about a third of their height immediately after flowering. Avoid cutting the stems too closely to the ground, as they serve as winter protection. The hollow stems also provide insects with a place to overwinter. Autumn asters can also be cut back in spring, in March or April, and the plant will sprout anew near the ground.

Tip: To maintain a lush growth habit throughout the flowering period, cut off wilted flowers promptly. This stimulates asters to produce new flowers.

When it comes to watering, Michaelmas daisies prefer soil that is not too moist. Do not pour water over the plants’ flowers or leaves − only water the soil around the base of your plants. Asters only need to be watered on occasion, such as during drought periods or in very sandy soils. New York asters are the exception to this, as their soil should always be kept moist.

We recommend fertilising autumn asters annually in spring. This keeps the soil fertile and enables the plants to grow vigorously. Our Plantura Flower Food is a good option, as its nutrient ratio is designed for magnificent flower growth. The high proportion of organic components promotes a healthy soil life for strong root growth. On top of this, the high potassium content helps to prevent fungal diseases such as mildew and ensures a sturdy base.

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Michaelmas daisies and powdery mildew

Powdery mildew on autumn asters is quite easy to recognise by the white-grey layer on top of the leaves. On top of the fact that leaves covered with powdery mildew are not able to photosynthesise very efficiently, the fungus also feeds on the plant’s assimilates and nutrients. Autumn asters afflicted by powdery mildew grow poorly and produce few flowers.

Various conditions can make your plants more susceptible to powdery mildew. This fungal infection usually occurs during cool, dewy nights, but this can also happen during otherwise warm weather with little rain. Asters that are in the shade in the morning or growing too closely together are particularly at risk. When leaves remain damp for a long time in the morning and there is poor air circulation, the chance of this fungal disease developing increases. Asters that are not getting enough nutrients are also at risk.

The first thing to do when powdery mildew first appears is to cut off the infested parts of the plant immediately. Do not dispose of the infected cuttings in the compost, but instead put them directly in the household waste. You can then gently treat the rest of the plant with milk or baking powder.

Are Michaelmas daisies hardy?

Autumn asters are generally hardy down to -35 °C or -45 °C, which corresponds to winter hardiness zone H2 and H3. When pruning Michaelmas daisies before winter, leave some of the stems behind so that the plants have some protection throughout the colder months.

Propagating Michaelmas daisies

It is easy to propagate Michaelmas daisies by dividing the plant at the roots. To do this, separate the rootstock by inserting a spade in the middle of the aster. You can then move the new plant to another suitable spot in your garden. Propagation by division also benefits the mother plant by promoting rejuvenation.

In addition to division, you can also propagate autumn asters by cuttings. Cuttings can be taken in spring, and will root easily in growing or cutting soil at room temperature.

Michaelmas daisies can also be grown from seeds. To do this, sow the seeds directly after harvesting in a garden bed or in pots outside. They will germinate within two weeks at 15 °C.

Are autumn asters poisonous?

Autumn asters are not poisonous to humans or pets. In fact, the flowers are edible and are used to decorate food, as are the leaves. However, store bought asters may be contaminated with fungicides or other pesticides, so are often not suitable for consumption.

In addition to Michaelmas daisies, there are many other wonderful plants that flower in autumn. Check out our article on beautiful autumn flowers for some more inspiration.