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.
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. Most bedding plants grown by gardeners fall into this category.