Annual, a term applied to plants which complete the whole course of their development in one season, within which they germinate, flower, perfect their seeds, and perish, never to spring again from the same root. The whole duration of life in the plants thus designated is indeed generally much less than a year, and in temperate and cold climates falls within the brief period of the summer months. Some species are generally annual, and others generally biennial; but whether an individual plant is annual or biennial often depends upon the accidental circumstance of the season at which the seed germinates, and may therefore be artificially determined by the time of sowing. Peculiar circumstances also sometimes convert annual into biennial, or even perennial plants; and those which are mere annuals in one climate, are perennial or even shrubby in another—e.g. the Castor-oil plant. Most kinds of corn are the produce of annual grasses; some of which, however, as wheat, in certain circumstances, prove of longer duration. The annuals cultivated in our flower-gardens are very numerous; and many species, both native and foreign, are among our most beautiful flowers.
In Gardening, annuals are divided into three classes—viz. hardy, half-hardy, and tender. The last named are those which can only be cultivated in the temperature of a stove or greenhouse, and consist of such as the Cockscomb (Celosia cristata), the Melon (Cucumis melo), and many others. The half-hardy class consists of those kinds that, while they will flower and perhaps perfect their seeds in the open air, need the assistance of artificial heat and protection in the early stages of their growth. The China Aster (Callistemma hortense), Tobacco (Nicotiana tabacum), Drummond's Phlox (Phlox drummondii), and Marigold (Tagetes), are familiar examples of this class of annuals. The first named or hardy class is composed of those that may be sown in the open ground, and will germinate and flourish from first to last without any artificial protection or aid. Nemophila Lupine (Lupinus nanus and others), the Large-flowered Flax (Linum grandiflorum), Candytuft (Iberis umbellata and others), the various Godetias, Gilias, and the Rocket Larkspur (Delphinium ajacis), are well-known members of the hardy group. So hardy are many of these that they may be sown in autumn and bloom the following spring, thus greatly prolonging the enjoyment of the flower-garden, as these will last in bloom till the ordinary spring-sown plants come in.
Californian annuals are unquestionably the most valuable for those who must rely solely on hardy flowers for the adornment of their gardens.