There are about 50 varieties currently available and all are selections of this species; unlike the more traditional Aster novi-belgii group which is largely composed of hybrids. Because of this there is less diversity in habit and flower. The stems are stiff and woody with coarse pale green leaves. Generally, plants are between 90 cm and 180 cm; except for ‘Purple Dome’ at up to 60 cm. New England Asters are popular garden flowers because of their restance to mildew attack. However, they are not ideal cut flowers due their habit of closing in the evening and are difficult to grow effectively in containers. There flowering season is September and October.
Aster novae-angliae is native from Quebec to Saskatchewan, South Carolina, Alabama, Kansas and Colorado. The species was introduced to Europe as far back as 1710 but never stimulated as much breeding interest among gardeners as A. novi-belgii. From 70 known cultivars only around 50 are still available to growers compared to around 300 A. novi-belgii cultivars of the 1000 bred since the 19th century. In the garden they add beautiful autumn colour to formal borders and are also perfectly suited to the more informal prairie style planting. Combined with grasses and other autumn flowering perennials, particularly perennial sunflowers and rudbeckias such as Rudbeckia nitida, they make a stunning autumn display.
These cultivars need to be planted in an open and reasonably sunny position to achieve peak flowering. They are naturally found in a wide range of sunny locations throughout their North American range. Sun is essential for the flowerheads to open fully, with many of the older cultivars rays closing up during wet and cloudy periods. However, most of the modern cultivars have rays that remain open to face all elements. The soil should be moisture retentive in the summer and can range from slightly acidic to quite alkaline. Light soils despite being less water retentive will grow excellent Michaelmas daisies but to ensure sufficient moisture is maintained over their shallow root systems a mulch is recommended. New England Asters are resistant to mildew; but, under stress conditions, such as long drought, lower leaves can be affected. A single spray with a mildew specific fungicide will usually clear this up.
They also tend to loose the lower leaves, leaving their stems looking brown and naked or even with brown leaves still hanging on. It is therefore advisable to use foreground planting. One way to hide the dying leaves on the stems is pinch out the tips of the young shoots around the outer edge of the clump when they are about 15 cm tall. This creates later and lower growth. It is possible to pinch all the shoots on a clump; making the whole plant shorter. This must be done early and only once, otherwise flowering will be too delayed. The need to stake depends on the prevailing conditions in any particular garden. Well grown plants with large crops of fowerheads will be well supported by the woody stems until they get drenched and blown about, when the need for canes will become apparent. Perversely less well grown plants, or more naturalised clumps with smaller crops of flowerheads should be more than adequately supported by the strong woody stems. This species appears to produce masses of fertile seed in this country so it is advisable to remove the old sprays in the autumn to avoid the good cultivars being swamped by seedlings. By late autumn old flowering stems will have dried on the plants and can then be cut back to ground level. If you do compost the material it is best not to use it on your Michaelmas daisies in order to reduce the risk of disease transference.
New England Asters can be left undivided for up to five seasons, and are best left for at least two. If space is short in your border it is advisable, with the more robust cultivars, to divide them every second season since many can form clumps of up to 1 metre diameter if left for four or five seasons. Also clumps that are divided more regularly will be less troubled by the loss of the lower leaves. Once the centre starts to die out the clump must be divided.
In the early spring when the new shoots are beginning to move but are not too far above ground the clumps can be lifted. Split the clumps into 15 cm segments using two forks or a sharp spade and then plant them straight into prepared ground. The divisions should be set out about 60 cm apart; very tall varieties will benefit from wider spacing. Once the root system is moving apply a light dressing of a good organic fertiliser. The plants can be mulched after spring or early summer rainfall to help with moisture retention. No additional feeding should be needed until application of a top dressing the following winter.
Young plants from 9 cm to1.5 litre pots can be planted in groups at a spacing between 45 cm and 60 cm apart.