There are many varieties of cool-weather-loving annuals that can be planted in fall. Although this same group of flowers is most commonly planted in early spring, they can also be planted in fall and will grow and thrive in the cool winter weather. They are known as "hardy annuals," and will bloom right through the winter months in milder climates. The shorter days and lower angle of sunlight in winter causes them to grow more slowly. They'll still produce flowers, but will require less water and fertilizer than annuals grown during the longer, warmer days of spring and summer.
Pansies and Violas
These close cousins are the first annual flowers to appear in garden centers every spring. They can also be planted in fall and will bloom all winter long in mild winter climates. Both pansies and violas can take a good amount of frost without missing a beat. They prefer partial shade, but can be planted in full sun for winter. Pinch off spent blossoms to encourage the plants to keep producing. If they start to grow a bit leggy, cut them back to about four inches high. They will rejuvenate themselves and bloom again soon.
Dianthus are available in many varieties, but the low-growing annual varieties commonly called "pinks" are hardy enough to grow and bloom through the winter months. Pinks grow less than a foot high and are a good plant to put in the front of the winter flower border. They produce copious amounts of single, clove-scented flowers in all shades of pink, from creamy white through deep magenta. If you leave the spent blossoms on them, the plants will self-seed in your garden.
Calendula's common name is "pot marigold," but it's not related to the tender French and African marigolds that are widely grown as hot weather annuals. Pot marigold is an herb that has been cultivated for medicine and seasoning since before the Middle Ages. Sometimes called the "herb of the sun," calendula's flowers, in shades of cream and bright yellow, follow the sun as it tracks across the sky, just like sunflowers do. They bloom prolifically, especially if you deadhead the faded flowers. Calendulas can withstand temperatures below freezing for short periods of time and will sometimes re-grow from their roots if the foliage is killed by a severe frost.