Botanically, an annual plant is a plant that usually germinates, flowers, and dies in one year. True annuals will only live longer than a year if they are prevented from setting seed. Some seedless plants can also be considered annuals even though they do not flower.
In gardening, annual often refers to a plant grown outdoors in the spring and summer and surviving just for one growing season. Many food plants are, or are grown as, annuals, including most domesticated cereal grains. Some perennial and biennial plants are grown in gardens as annuals for convenience, particularly if they are not considered cold hardy for the local climate. Carrot, celery and parsley are true biennials that are usually grown as annual crops for their edible roots, petioles and leaves, respectively. Tomato, sweet potato and bell pepper are tender perennials usually grown as annuals.
Ornamental annuals are often called bedding plants. Annuals are often used in gardens to provide splashes of color, as they tend to have a longer season of bloom than hardy herbaceous perennials. Some tender perennials commonly grown as annuals are impatiens, wax begonia, snapdragon, Pelargonium, coleus and petunia. Some biennials that can be grown as annuals are pansy and hollyhock.
One seed-to-seed life cycle for an annual can occur in as little as a month in some species, though most last several months. Brassica rapaOilseed rape can go from seed-to-seed in about five weeks under a bank of fluorescent lamps in a school classroom. Many desert annuals are termed ephemerals because their seed-to-seed life cycle is only a few weeks. They spend most of the year as seeds to survive dry conditions.
Examples of true annuals include maizecorn, lettuce, pea, cauliflower, watermelon, bean, zinnia and marigold.