The Aster are hardy herbaceous perennials and half-hardy annuals.
The perennial asters may conveniently be considered under four distinct headings.
Dwarf early-flowering kinds derived from such species as Aster Amellus and Aster Thomsoni.
The taller, later-flowering varieties with comparatively large blooms, which have been raised from the North American species Aster Novi Belgii and Aster Novse Anglias, and together with the next group are popularly known as Michaelmas daisies.
The late-flowering kinds with narrow foliage and ele¬gant habit and large panicles of starry flowers have their origin in such species as Aster ericoides, Aster cordifolius, diffusus, and Trade-scanti.
There are also miscellaneous low growing kinds most suited to the rock garden or the extreme front of the herbaceous border.
The annual asters are derived from a Chinese plant botanically known as Callis-tephus hortensis. Numerous distinct types have been evolved by hybridisation and selection, but all have similar cultural re¬quirements.
All the perennial asters are extremely hardy and will grow in any ordinary garden soil, though in the case of the choicest alpine species it is advisable to add a liberal quantity of sand and a little leaf-mould or peat moss litter if the natural soil is of a heavy, wet, or sticky nature. For the other kinds the only preparation necessary is good deep digging and the incorporation of a little well-rotted manure into the lower spit. The taller kinds, such as hybrids of Aster Novi Belgii, cordifolius, etc., should be staked early with long bamboo canes. Even some of the dwarf hybrids of Aster Amellus and Aster Thomsoni will pay for some support, which may be provided in the form of short, brushy sticks. Clumps increase in size very rapidly and should be divided every two or three years. If very fine blooms are desired, it is advisable to thin the growths in spring, leaving only three or four to each plant according to its strength. The most suitable planting seasons for most kinds are October, March, and early April, but varieties of Aster Amellus should only be planted in spring and never in autumn.