The general definition of an annual is a plant that germinates from seed, flowers, and sets seed, and dies in one season. Then to complicate matters some annual plants are referred to as hardy annuals or half-hardy annuals. Some half-hardy perennials are also grown as annuals.
Like the general definition, a hardy annual is a plant that completes its lifecycle in one year. Hardy annuals do not need to be raised indoors. They can easily be sown in situ (directly into their garden location). Hardy annuals can tolerate light frost without injury. Some familiar hardy annuals include calendula, cornflower, annual larkspur, and nigella.
Half-hardy annuals also germinate, grow, flower, and die in one year. But, they require a longer period of growth to do so. Half-hardy annuals are started indoors 4 to 8 weeks before the last frost date to give them the extra time they need to mature and begin flowering. They are frost tender and must not be planted outdoors until all danger of frost has passed, usually early- to mid-May in Iowa. Most bedding plants grown by gardeners fall into this category.
Half-hardy perennials, such as dahlia, gazania, gerainium, gerbera, and tuberous begonia are often treated as annuals. Seeds must be sown early (January or February) to obtain blooming plants by summer. Some, like gazania, are treated as half-hardy annuals and are discarded when a hard frost occurs. Others, like geraniums, can be lifted before a frost, repotted or repropagated by cuttings, and grown indoors during the winter. Still others, like dahlias and tuberous begonias, are lifted and their root structures stored in a cool but frost-free location.
Gardeners can grow a variety of plants for a single, annual season of enjoyment. However, a deeper look may reveal something more than the typical annual.
This article originally appeared in the April 26, 1996 issue, p. 59.