As the name implies, annuals last for just one year. They're the bright blooms you'll often see up front in nurseries and home centers. They grow and bloom quickly, providing instant impact. They're ideal for filling in empty spaces, and most will grow in all climate zones. But because they only last for a season, you'll need to replace them yearly.

Annuals are sold as either cool-season annuals or warm-season annuals. Cool-season annuals provide early color in the spring and often bloom throughout the winter in mild-winter climates. Popular cool-season annuals include pansies and sweet peas.

In mild-climate areas, plant these in late fall for winter bloom or in very late winter or early spring for spring bloom. In cold-climate areas, plant as soon as the ground can be worked.

Warm-season annuals flourish during the late spring, summer, and early fall. Favorites include sunflowers and zinnias. Because these plants can't handle cold, they need to be planted later in the growing season.

In mild-climate areas, plant in mid-spring; in colder climates, set out plants once there is no more danger of frost.

In the Southwest, however, where winters are warm and summer temperatures can stress even the hardiest plants, planting seasons may be reversed. Many warm-season annuals are planted in the fall for winter bloom.

Because of their rapid growth, annuals need more nutrients throughout the growing season than do other plants. Apply a complete fertilizer when planting. If you're in a mild-winter climate, add a nitrogen fertilizer once the plants start flowering and in late summer. In cold-winter areas, feed once the plants start flowering. Be careful not to overfertilize.

You'll usually find annuals sold in 6-packs or cell-packs, or in 4-inch pots. Look for smaller and bushier plants with strong-colored foliage. The roots should not be overgrown or matted. Although plants with plenty of flowers are tempting, instead choose ones with fewer flowers or even just buds. They will have more energy to put into establishing good roots.

Keep in mind that some plants sold as annuals aren't really annuals. In cold-weather climates, tender perennials such as common geraniums (Pelargonium) that don't survive freezing temperatures are sold as annuals. And biennials such as foxglove (Digitalis), plants that grow over a two-year cycle, may also be sold as annuals when they start blooming.