Cultivation
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 to those plants with S. pringlei in their heritage such as ‘Ochtendgloren’, which, in suitable conditions, will be hardy below -10ºC. Good light is important for the best flowering, but many such as ‘Chieftain’ or S. lateriflorum will tolerate partial shade – that is, light, dappled shade from deciduous shrubs (not heavy evergreens). 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.
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.
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. 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’.
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 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, busier 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.