Gardens

All about asters (or the Michaelmas daisy) and how to grow them

Indispensable for their late-season flowers, asters or Michaelmas daisies fill the autumn garden with colour and wildlife. Hazel Sillver looks at the history of these long bloomers, as well as the best to grow and how.  

Aster ‘Mönch’ at the gardens of St Giles House in Dorset

Andrew Montgomery
  • Common names: Aster, Michaelmas daisy
  • Botanical names: Aster, Symphyotrichum, Eurybia
  • Family: Daisy (Asteraceae)
  • Type: Perennials
  • Flowering time: Late summer and autumn
  • Planting time: Spring
  • Height: 30cm-1.5m (1-5ft)
  • Spread: 30cm-90cm (1-3ft)
  • Aspect: Full sun or semi-shade
  • Hardiness: H6-H7
  • Difficulty: Easy to average

Producing clouds of colourful daisies during the autumn months, whilst the majority of the garden is browning into hibernation, asters are stalwart perennials. The most dazzling of the vast range available are the lilac and blue forms, which glow incredible hues beneath the grey skies and sit so well with autumn’s golden grasses. The soft-pink forms are also beautiful, providing warmth when the weather cools and the perfect foil for falling copper leaves.  

Within the 600 or so species and umpteen hybrids of aster, there are also darker shades of pink and purple, as well as white forms, and the plants produce a great range of structure: including upright, bushy, dense, and airy options; some tall and some short. They bloom over a long period, sometimes from August into November, providing hoverflies, bees, and butterflies with vital nectar before winter sets in. Since the peak of this flowering occurs around the feast of Archangel Michael in late September, they are commonly known as Michaelmas daisies. Hence the old rhyme rings, ‘The Michaelmas daisy, among dead weeds, Blooms for St Michael’s valorous deeds. And seems the last of flowers that stood, Till the feast of St Simon and St Jude.’ The latter feast day is held on 28 October, when many asters are still blooming away.  

The name ‘aster’ is the Ancient Greek word for star and given because the radiate petals of the flowers give them a starry look. In mythology, they grew when Asteria, the Greek goddess of the stars and the mother of Hecate, wept tears of stars from the night sky. In the old world, the plants were ceremonially burnt at the end of autumn, as the smoke was believed to cast out evil spirits and flush out snakes.  

Although several perennials are still commonly known as asters, it is no longer the correct horticultural Latin classification for many of them. A swig of espresso is required before trying to get to grips with the name changes. A few years ago, Aster novi-belgii (the true Michaelmas daisy) became the ridiculous mouthful Symphyotrichum novi-belgii; likewise, A. novae-angliae (the New England aster) and A. ericoides (the heath aster) are now Symphyotrichum. Continuing the tongue-twisting, A. acris was re-named Galatella sedifolia, and A. macrophyllus ‘Twilight’ morphed into Eurybia x herveyi. But others (such as A. x frikartii) remain Aster. Many nurseries ignore the name changes and still refer to them all as asters to prevent frightening customers.  

 The vast majority are native to North America or Eurasia. A few are British wildflowers (including the sea aster, Tripolium pannonicum), but the key species were introduced here in the early 18th century and became beloved plants in Victorian and Edwardian gardens. In the early 20th century, naturalistic gardener William Robinson used asters ‘as graceful wreaths’ to billow ‘in the October winds . . . making natural and picturesque effects’, and garden designer Gertrude Jekyll planted a whole border of asters at her home, Munstead Wood.  

 They eventually fell out of favour – probably due to the susceptibility some have to mildew and the invasive vigour of others. But, in recent years, asters have enjoyed a revival via the trend for prairie-style planting. Since many hail from the US prairies and because there are now so many garden-worthy forms that behave themselves, asters have become primary plants in contemporary meadow-style plantings. They pair well with grasses and offer a lovely informal charm, and when they blaze lavender-blue on overcast autumn days, they are hard to beat.  

Which asters to grow 

The flowers of Michaelmas daises range in size, from the wonderful violet-blue blooms of Aster x frikartii ‘Mönch’, which can reach 5 centimetres, down to the tiny white and pink stars of Symphyotrichum lateriflorum var. horizontale that are held on horizontal stems, producing a pleasing bushy effect. In general, the bigger-bloomed varieties (such as A. amellus ‘King George’) create a traditional look, which works well in cottage gardens; while the small-flowered forms (for example, S. cordifolium ‘Chieftain’) produce a more contemporary mood.  

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Garden designers love the little lilac-pink daisies of S. ‘Coombe Fishacre’ and S. ericoides 'Pink Cloud', which both have a shrubby habit, and use the airy structure of pale-blue S. turbinellum and sugar-pink S. ‘Vasterival’ to create lightness and movement. All asters pair well with grasses to add splendour to the modern autumn garden. For instance, at Great Dixter in East Sussex, S. lateriflorum var. horizontale blooms beside the golden wands of Calamagrostis × acutiflora 'Karl Foerster' and feathery plumes of Miscanthus sinensis 'Malepartus'.  

 For a blast of colour, the generous rich-purple daisies of S. novae-angliae ‘Helen Picton’ and bold cerise-pink S. novae-angliae ‘Andenken an Alma Pötschke’ are a joy. Garden designer Piet Oudolf, who made the prairie style popular, favours Eurybia x herveyi (syn. Aster ‘Twilight’) for a mass of soft lavender, which glows an enchanting shade of blue at dusk.  

 There are double-flowered forms – such as the gorgeous purple-blue S. novi-belgii ‘Marie Ballard’. But the single-flowered asters give a more modern feel to the border, and there are endless varieties to choose from. A reliable all-rounder is S. ‘Little Carlow’, which is a cloud of single violet-blue daises in early autumn. For advice on the best choice for your garden and for good quality plants, order from a specialist supplier, such as Old Court Nurseries.  

How to plant asters 

If possible, choose an open site in full sun. However, many forms – including the bulletproof A. × frikartii ‘Mönch’ – will bloom well in semi-shade. Ensure the soil is well-drained, fertile, and moisture retentive by digging in organic matter (such as peat-free compost) before planting. Asters prefer neutral to alkaline soil; if you are on very acid soil, the more compact forms (such as A. × frikartii ‘Flora’s Delight’, A. amellus ‘Veilchenkönigin’, and S. novi-belgii ‘Remembrance’) can be grown in well-drained pots.  

How to grow asters 

Deadhead early in the season to encourage a second flush of flowers, but leave the later blooms to provide a habitat for insects over winter and food for birds. Taller forms may need staking in exposed borders. Mulch annually in spring on all soils; and on lighter soils (such as sand), add a general fertilizer (such as Vitax Q4) once a year. Divide plants regularly in spring in order to maintain health and flower power and control their size. This is required every 1-3 years for S. novi-belgii; every 3-5 years for S. novae-angliae, S. cordifolium, S. lateriflorum, and S. ericoides; and every 4-6 years for A. frikartii, A. pyrenaeus, and A. amellus.  

Aster pests and diseases 

Some forms of S. novi-belgii are prone to powdery mildew. Prevent it by avoiding a very hot south-facing position, give the plant plenty of elbow room to ensure there is good air flow, divide regularly, and mulch with organic matter (such as peat-free compost) every spring.  

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