Michaelmas daisy: the best Michaelmas daisies to grow

By Daisy Bowie-Sell

Published: Saturday, 06 August 2022 at 12:00 am

It would be hard to imagine autumn without the soft, pastel drifts of the small-flowered Michaelmas daisy. The individual flowers of Michaelmas daisies may be small, but they are produced en masse, transforming the plants into cloud-like forms.

Small-flowered Michaelmas daisies are herbaceous, clump-forming perennial members of the Asteraceae family. They are drawn from five species, all part of the largely American genus Symphyotrichum, (previously Aster). They are distinguished through their flower size and profusion of blooms, along with their bushy habit. They are native to the USA and southern Canada.

While some groups, such as the prolific New York Michaelmas daisies, are grown for their striking individual flowers or depth of colour, the small-flowered Michaelmas daisies offer a softer approach with their multitude of flowers, arching sprays and interesting foliage.

Highly drought tolerant and resistant to mildew, and often able to flower in part shade, Michaelmas daisies are a welcome addition to the garden.

Season The main flowering period is from early to mid-autumn.
Conditions Best in sun or light shade in reasonable garden soil.
Hardiness Most have a hardiness rating of RHS H7, (tolerating temperatures to below –20ºC) and are suitable for gardens in USDA 4a-9b.

How to grow Michaelmas daisy

Small-flowered asters flourish in good, humus-rich garden soils and will tolerate and even thrive in poorer soils, as long as they do not dry out too much in hot conditions or get waterlogged in winter. Winter drainage is particularly important. In very hot, dry conditions, S. ericoides cultivars such as ‘Blue Star’ are often the toughest. S. cordifolium cultivars and hybrids such as ‘Little Carlow’ enjoy a bit more moisture.

Good light is important for the best flowering, but many such as ‘Chieftain’ or S. lateriflorum will tolerate light, dappled shade – that is, light, dappled shade from deciduous shrubs (not heavy evergreens).

Where to plant Michaelmas daisy

In borders, small-flowered asters, particularly those with coloured foliage, such as ‘Lady in Black’, combine well with spring bulbs – the purple colouring acts as a foil for pale-flowered bulbs, such as Tulipa linifolia ‘Bright Gem’. Some forms make excellent border edging, for example, S. lateriflorum var. horizontale as in the Peacock Garden at Great Dixter, where it is used as a pseudohedge. Combined with other herbaceous plants and shrubs, they are invaluable for extending the season, the pastels helping to bring the rich autumn colours of Cotinus and Acer to an ever-more
striking crescendo. Combined with ornamental grasses, they can add a charming pop of colour and an important change in texture.

In raised beds and hanging baskets, the prostrate ‘Snow Flurry’ will happily trail over the edges. Growing small-flowered asters in garden borders may be the most common form of cultivation, but many can also be easily grown in containers, extending the season for terrace displays. The slightly shorter, bushier forms tend to excel in a generous container. Importantly, almost all make excellent cut flowers – so we can enjoy a little bit of autumn beauty in the house as well.

How to propagate Michaelmas daisy

As well as improving the health and vigour of the plant, division is the easiest way to propagate small-flowered asters. Lift clumps for division every three to five years in spring, removing any old and woody material, and replanting or potting up the divided sections.

Michaelmas daisy problems

Most species and cultivars show good levels of resistance to powdery mildew, but this does vary. In general, those with rougher foliage are less susceptible to mildew than those with very smooth foliage, but in very hot, dry conditions it can appear on some plants. To reduce the risk, apply a good mulch in the spring to slow down the rate of water loss and divide the plants on a fairly regular basis. Remove any diseased foliage as soon as
you see it to prevent spread.

While most small-flowered asters are relatively untroubled by pests, it is worth watching out for slugs in early spring on young, clump-forming plants that are slow to establish, such as ‘Photograph’.