Perennials

These are plants that die down during the winter, butspring up and produce new stems annually. Some, as for instance
Antirrhinums and Pansies, flower the first season, but usually they do
not bloom till the second season. Many of the species improve by age,
forming large clumps or bushes. The stock is increased by division
of the roots, which, if judiciously done, improves the plant. Like
annuals, they are divided into classes of Hardy, Half-hardy, and
Tender plants.
Hardy perennials do not require artificial heat to germinate the
seeds, or at any period of their growth, but are the most easily
cultivated of all plants. Seed may be sown from March to midsummer,
transplanting in the autumn to their flowering quarters; or it may
be sown in August and September in a sheltered position to stand the
winter.
Half-hardy plants require artificial heat to germinate their seed, and
must be gradually introduced into the open. They may be sown during
March and April in frames or a greenhouse, when many will bloom the
first season. If sown between May and the end of August they will
flower the following spring and summer. They require protection during
winter, such as is afforded by a cold pit, frame, or greenhouse, or
the covering of a mat or litter. Tender perennials may be sown as
directed above, but the plants should be kept constantly under glass.
Some perennials, such as Pinks, Carnations, Saxifrages, etc., do
not die down, but retain their leaves. These are called evergreen
perennials.