Horticulture Magazine

Asters ‘Michaelmas Daisies’ Plant Care & Growing Tips

purple and yellow asters flowers with pollinators

Asters Overview

Official Plant NameAsters
Common Name(s)Michaelmas Daisies
Plant TypePerennial / Annual Flower
Native AreaEurasia
Hardiness RatingH6-H7
ToxicityNone
FoliageDeciduous
FlowersStar-shaped flowers in different colours
When To Sow / Plant OutMarch, April, May
Flowering MonthsAugust, September, October
When To Pinch Out TopsJuly
When To DeadheadSeptember, October
Sunlight

Preferred
Full Sun (some Partial Shade)

Exposure
Exposed or Sheltered

Size

Height
0.1 – 0.5M

Spread
0.1 – 0.5M

Bloom Time
August – October

Soil

Preferred
Most Soil Types

Moisture
Moist but well drained

pH
Any

Asters, also known as ‘Michaelmas Daisies’, are popular herbaceous flowering perennials that look wonderful in many UK gardens.

Whether you are trying to create a traditional cottage garden feel, or more modern prairie style planting, asters can be a go-to choice. They look lovely, and can be great for the bees, butterflies and other beneficial insects that visit your garden. And of course, what is good for the wildlife in your garden is good for you as a gardener too – since the rich biodiversity makes it easier for you to grow your own food and derive other yields from your organic garden.

Plant Background

purple Aster amellus flowers blooming in a garden
Aster amellus

The genus Aster once included over 500 different species of perennial flowering plant from Eurasia and North America. However, research during the 1990s led to North American species being reclassified into different genera – such as, for example, Eurybia and Symphyotrichum.

Nonetheless, these North American species are usually still referred to as asters. So in this article, we will include these species too – since the care and growing tips for these plants are often the same or very similar to the around 180 Eurasian species in this genus.

The term ‘Aster’ comes from the ancient Greek for ‘star’. The name refers to the shape of the flower head. The genus Aster is part of the large Asteraceae plant family, also known as the ‘daisy’ or ‘sunflower’ family. This is a huge plant family with over 32,000 different species, many of which are common garden flowers.

There is actually only one native Aster in the UK – the Aster tripolium, or sea aster. Another species formerly known as Aster linosyris is now known as Galatella linosyris.

But many asters from Europe and North America, and hybrids derived from them, can be grown easily and successfully in UK gardens.

Why Choose Asters For Your Garden?

Asters take their common name – Michaelmas Daisies – from the fact that they mostly bloom in late summer or early autumn. They can be excellent choices where you want to make sure you have flowers in bloom in your garden over as much of the year as possible. They take over where summer flowering blooms leave off. And can bridge the gap between the summer and autumn seasons in your garden.

Asters can grow in all hardiness zones, and can be useful for attracting wildlife in your garden. They can be beneficial for pollinators, and are important food plants for the larvae of a number of common butterflies and moths.

Another benefit of growing asters, of course, is that these perennials will return to bloom in your garden year after year. And like many other perennial plants, they will require very little care, so could be a great choice for a relatively low maintenance garden scheme.

Common Varieties

beautiful butterfly sat on Symphyotrichum novi-belgii flowers
Symphyotrichum novi-belgii attracting a butterfly.

There are a great many different asters that you might consider choosing for your garden. Some great options for UK gardeners include:

  • Aster alpinus
  • Aster amellus
  • Aster x frikartii (A. amellus x A. thomsonii)
  • Aster herveyi (Eurybia x herveyi)
  • Aster tongolensis (e.g. ‘Beggarten’)
  • Symphyotrichum laeve (e.g. ‘Calliope’)
  • Symphyotrichum novae-angliae (e.g. Harrington’s Pink’)
  • Symphyotrichum novi-belgii (e.g. ‘Dasthree’, ‘Island Series’, ‘Samoa’, ‘Algar’s Pride’)
  • Symphyotrichum ‘Ochtendgloren’ (pilosum var pringlei hybrid)

When choosing Asters for your garden, the size and hues of the blooms are one thing to consider. But you should also think about the typical height of the plants. Since this will determine whether they will work best towards the back, in the middle, or near the front of a bed or border on in a container. Some asters are much taller than others.

Where To Place Asters in Your Garden

a flower bed with absinthe wormwood, ornamental grass and asters
A perennial border with asters and grasses.

Asters look great in herbaceous perennial borders, especially alongside other perennial flowering plants and meadow grasses. They are right at home in a prairie planting scheme. The flowers are cheery and colourful, and a number of varieties also make excellent cut flowers. They can be great for a traditional cottage garden. But many varieties can also work well in a more contemporary scheme.

These perennial flowers will thrive in almost any soil type, ideally one that is moist but well-drained to well-drained. They will usually do best in areas of full sun though many varieties can also cope with partial or dappled shade. Many varieties are also excellent for growing in containers.

Remember to place asters in a location which suits their appearance and form – and note their eventual height when deciding where to place them. Avoid placing taller asters in a location that is too exposed, where they may be subject to wind damage.

A border of asters and tall perennial grasses can also have wider applications. For example, it can be used to ‘borrow’ landscape from beyond the edges of a rural garden – tying in the garden with farm fields beyond.  A border of perennial flowers and grasses might also screen another part of the garden from view, or partially obscure a view without entirely blocking it.

Sowing and Planting Asters

Asters can be grown from seed or from cuttings. If you are sowing seeds, you should typically sow asters in March or April. However, it is more common to purchase pot grown asters here in the UK.

If you would like to take cuttings from an existing aster, you should do so between April and August. Keep these moist and in a sheltered location and if they have rooted successfully, you can plant out your cuttings in spring to flower the following year.

Aster seedlings or cuttings should be planted out, typically, between March and May. This is also the time when you should plant out asters as potted plants that you have purchased for your garden.

Asters should typically be placed for a spacing of around 40cm between plants.

What To Plant With Asters

Asters are versatile perennials that will work well alongside many other herbaceous perennials in a bed or garden border.

Asters look fantastic alongside other herbaceous perennials for summer/autumn including:

  • Achillea millefolium
  • Caryopteris
  • Chrysanthemums
  • Echinacea
  • Helenium
  • Phlox
  • Rudbeckia
  • Salvias
  • Veronicastrums

And alongside a wide range of ornamental grasses such as:

  • Stipa
  • Molinia
  • and Calamagrostis, for example.

Caring For Asters

Caring for asters does not require a lot of work. In fact, when placed in the right locations, asters will require very little care and be a great choice for a low-maintenance garden.

Watering

Keep the soil well-watered. But do not let asters sit with wet feet. Watering problems are the most common reason for one of the main issues that aster growers can encounter – mildews. These flowering plants can be rather prone to mildew problems. And over-watering is one of the most common causes.

Typically, in normal UK conditions, watering in addition to natural rainfall will not be required (unless they are grown in containers). In drought conditions, or when growing in containers, a thorough soaking every two weeks should be sufficient to see them through hot and dry periods.

Mildew Issues

Consistent watering, but a well-draining medium or soil, and good air-flow around the plants can help to reduce the likelihood that this problem will occur. Avoid overcrowding your plants. And do not water too much.

If you experience a lot of problems with mildew in your particular garden, then it could be a good idea to look for more mildew-resistant cultivars or varieties.

Fertilisation

Asters typically do not require particularly high levels of nutrients. And fertilizers will not typically be required. Usually, it will be enough to simply mulch around the plants with a good quality organic mulch, which will act as a slow-release fertilizer over time. When growing in pots, however, or to improve very poor soil, you may wish to add blood fish and bone or another organic fertilizer a couple of times during the flowering period.

Deadheading and Cutting Back

Deadheading the plants and getting rid of spent flowers can also help to reduce the incidence of any problems of this type. Deadheading will also keep them looking good for longer. And will encourage them to produce more flowers.

To get as many flowers as possible from your asters, you should pinch out top shoots at midsummer. Then deadhead as you go. Then cut back your asters hard after flowering finishes in autumn.

Division of Mature Plants

Asters should also be divided every four years or so. This will help the plants to retain their vigour, and prevent clumps from becoming overly congested. It is best to divide mature asters in the spring, just as new growth begins.

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