Annual flowers are those plants that complete their life cycle in one season. Annuals that thrive in winter are cool-season annuals. Depending on the climate, these are either hardy or half-hardy annuals, plants that can withstand small periods of freezing temperatures. Annuals provide consistent color to the garden, especially in winter when many perennials are dormant. Many areas of California enjoy mild weather even in winter. Annuals are usually planted in the fall for winter flowers.
With their colorful, large flowers, and wide range of colors, pansies (Viola tricolor) are one of the more popular cool-season annuals in California. Pansies are a small annual, growing only to 12 inches tall and wide. The leaves are oval and green. The flowers bloom in single and bi-colors. Some pansies have a distinctive markings referred to as a "face." Colors include shades of pink, yellow, white, purple and orange. These annuals are slightly fragrant early in the morning and at dusk, according to Clemson University. In mass planting, pansies provide a blanket of color in the garden. Pansies also thrive in containers. These annuals will bloom all winter long, provided they are protected from prolonged freezing temperatures. They prefer partial sun and moist, but not wet, well-drained soil.
Native to the Mediterranean, snapdragons are considered a cool-weather annual that thrives in California's mild winters. Some varieties of snapdragon reach a height of 3 feet tall, but dwarf cultivars, reaching only 6 inches tall, are also readily available. Flowers bloom in a wide range of colors from white to orange, pink and red. The only color lacking in the snapdragon range is blue according to UC Davis. These plants are not heat-tolerant but thrive in full sun during the fall, winter and early spring. Multiple flowers bloom on tall stalks above green foliage. Snapdragons make excellent cut flowers for winter bouquets. These annuals are sold as seedlings in local nurseries. Seeds are also available.
Sweet alyssum (Lobularia maritime) is a hardy annual, meaning it will hold up to periods of freezing temperatures. Small white, yellow or purple flowers bloom in clusters on slender pale green stems creating a carpet of color. Sweet alyssum grows in partial to full sun and reaches only 6 inches tall. This annual self-seeds and multiplies rapidly, according to University of Illinois. Plant sweet alyssum in well-drained soil along the edges of walkways or around taller plants as a ground cover. The flowers have a delicate fragrance and attract butterflies to the garden.