This group can be divided into the five North American species; Aster cordifolius, Aster ericoides, Aster pringeli, and Aster lateriflorus, and then the garden and cut flower hybrids. The majority bear graceful, many branched sprays with clouds of tiny star-like flowerheads. Most give beautiful displays in late September and through October. They are not especially prone to mildew and even the larger hybrids are excellent for cutting. They are usually slow growing and require a fertile soil which is free draining over winter. Supply of most sorts is limited so early ordering is essential.
Native from southern Canada to Georgia in the south, and westward this species is found growing in clearings of woods and thickets. It is one of a very small selection of Asters which are tolerant of a little shade. The leaves are thin, dull green and slightly hairy and heart-shaped on the lower parts of the stem. Most of the cultivars reach 120 cm in height, although ‘Chieftain’ is capable of exceeding 150 cm. The flowering sprays form graceful spires covered in tiny flowerheads, usually no more than 13 mm diameter. The sprays last well when picked but the disc florets do change rapidly from pale yellow to purple shades. The Aster cordifolius hybrids can be grown in the same way as A. cordifolius but they do need open, sunny positions to flower at their best.
They have good resistance to mildew attack and the species can tolerate a little shade, such as dappled shade from deciduous trees. Heavy shade from evergreen shrubs and trees will prove to be too much particularly through the winter. Although tough enough to survive in dry soils a lack of moisture will lead to badly discoloured foliage and a reduced number of flowerheads.
It is not necessary to divide them more than once every three years. The clumps should be split into 10 – 15 cm sections and then re-planted in humus-rich prepared soil. It is possible to divide right down to single shoots but better results are achieved from larger sections. Redundant woody sections of root and old stems can be removed during division.
Native from Maine to Ontario, Florida, Minnesota and Missouri this species is found growing in dry soils. The leaves are linear to linear-lanceolate, up to 6 cm long. The clumps are vigorous and compact ranging from 30cm up to 90 cm. Most cultivars bloom in mid-autumn with masses of tiny flowerheads on erect or arching, well branched sprays. They are useful for flower arranging and are on the whole very easy to grow. They are happy not only out in the garden but the majority also make good container plants.
Mildew is not a major problem but attacks do occur in some years, so a minimum amount of preventative spraying might be useful to ensure clean foliage. Although quite happy left in one spot for years the best display will be achieved by dividing the clumps every three or four years. This should be done in early spring and the sections re-planted in well prepared soil.
This species is very similar to Aster ericoides and is of considerable importance to gardeners and commercial growers. Native to Massachusetts and Vermont to Wisconsin it is found growing along riverbanks particularly in rocky places. The clumps are small and not very strong with oblong to lanceolate basal leaves and more linear stem leaves. The white flowerheads are bourne in broad panicles on upright sprays in mid-autumn. The cultivars are perfect for the cut flower trade; the best known being ‘Monte Cassino’ also known as ‘September flower’, however, they do not make particularly strong garden plants. If to be grown in the garden the soil needs to be light but with good moisture through the growing season and very good winter drainage. Mildew poses few problems when they are grown outside but preventative spraying is necessary if under cover. To maintain the best flowering sprays the plants should be divided every year. Many cultivars are produced for the cut flower trade but few are likely to make good garden plants.
Native from southern Canada down through north-eastern USA to Texas this species grows in dry and moist soils, in open situations as well as thickets and along woodland edges. The flower sprays are wiry and bushy with the lower branches being almost horizontal. The flowerheads are small and produced late in the season. They are set on the upper sides of the branches and are often only 13 mm in diameter, although some of the cultivars are now approaching 2 cm in diameter. The disc florets are often the most prominent feature of the flowerhead. The lower leaves tend to be oval while the stem leaves are lanceolate. They show bronze-purple colour in spring and are then green. The clumps are strong, woody and quite compact with heights ranging from 40 cm to 150 cm. The compact cultivars make very good container plants.
Although the typical species will tolerate shade the cultivars are best in fertile soil with summer moisture and a sunny situation. Mildew is rarely a problem particularly if there is no host plant in the immediate vicinity. Mature clumps are will support the flowering sprays without the need for staking. The plants do not require regular division being quite happy left for a number of years. When they are divided simply split into smaller sections and remove any hard wood from the central regions.