Annual flowers are categorized according to their tolerance to cold weather and frost. Hardy annuals are tolerant to light frost and some freezing temperatures. Half-hardy annuals tolerate cold, damp weather, but are damaged by frost. Tender annuals are native to tropical areas and are sensitive to cold soil temperatures. Annual plants can be planted among perennials or shrubs to fill in gaps while waiting for the larger plants to grow. They are used as accents in planters and boxes. Plant them with bulbs to disguise the fading foliage of spring bulbs.
California poppy (Eschscholzia californica) has cup-shaped flowers in orange, yellow, white, pink and red. Pinching off developing seed pods extend the flowering season. The California poppy blossoms open during the day, but close in cloudy weather and at night. They thrive in full sun and sandy soil.
Common stock (Matthiola incana) produce fragrant blossoms in clusters growing on flower spikes. These blooms are white, pink, red, yellow and purple. This fast-growing annual has upright stems and lance-shaped leaves. It likes full sun conditions.
Cornflower (Centaurea cyanus) is also commonly called bachelor's button. This in an easy to care for hardy annual. Cornflowers are bushy with thin stems and fluffy flower heads that are 1 to 2 inches wide. The blossoms are white, blue, purple, pink or red. Pinch off dying blooms to prolong the flowering season. Cornflowers thrive in full sun and partial shade.
Dahlias, or Dahlia hybrids, are bushy plants with flowers that are 1 to 8 inches across. Dahlias flower in nearly every color except true blue. They even have a near black blossom. Pinching off dying blossoms extend the flowering season. Dahlias enjoy full sun conditions.
Petunia (Petunia x hybrida) grows in clumps of upright or trailing stems. The leaves are green ovals and it has funnel-shaped flowers. Petunias produce flowers in every color of the rainbow and some blossoms have stripes. Petunias grow well in full sun with light shade.
Marigold, or Tagetes hybrids, produces 2- to 4-inch flowers over bushy mounds of lacy, green leaves. Remove dying blooms to prolong the blossoming time of a plant. Marigolds do well in full sun with light shade in the afternoon.
Sunflower (Helianthus annus) is a hardy annual with large, showy blossoms and edible seeds. Their leaves are heart-shaped and the flowers are flat, daisy-like. The cultivars range from dwarf varieties to giant varieties. Sunflowers like to be planted in areas with lots of sunlight.
Sweet Williams (Dianthus barbatus) have lance-shaped green leaves. Their stems are topped with dense clusters of five-petal blooms. Sweet William flowers are red, pink or white. They like full sun or partial shade conditions.