Cool-season annuals are those short-lived perennials, biennials or one-year plants that prosper when temperatures are below 60 degrees F. Depending on the severity of winter in your location, these plants can be overwintered outdoors and will flower nicely from December to February if bitter cold is avoided. The more southerly the location and milder the overnight temperatures, the more flowering plants you'll have to enjoy.
In very cold parts of North America, where snow cover is common from December through February, and gardens are considered in USDA plant hardiness zones 1 through 5, no annual flowers can consistently survive and bloom. In protected micro-climates, Johnny-jump-ups (Viola tricolor) will prosper and bloom as temperatures allow, around fences or building foundations with southern exposure. Use perennial bulbs, such as daffodils and crocus, for winter color.
Cool but Mild-Winter Regions
In more southerly locales, in USDA plant hardiness zones 6 through 8, ornamental plants grow and bloom in the chilly but mild subfreezing winters. As long as days are between 25 and 40 degrees F, you'll find success with pansies and Johnny-jump-ups (Viola spp.), snapdragons (Antirrhinum), ornamental cabbages and kales (Brassica), wallflowers (Erysimum), pinks (Dianthus) and Dusty Miller (Senecio).
Unseasonally cold or prolonged subfreezing temperatures can can dieback even on these cool-season annuals, but often they will recover and continue growth past February and excel into March.
In the subtropical reaches of North America, in USDA zones 9 to 11, the threat of frost exists. Here, choose from a broad selection of flowers (including those mentioned in Section 2): sweet alyssum (Lobularia), annual phlox (Phlox drummondii), spider flower (Cleome) and Gerbera daisy (Gerbear jamesonii).
Petunia, zinnia, begonia, French marigold and impatiens are also possible if weather is consistently mild, with temperatures between 40 and 70 degrees F from midwinter onward, and if the winter is dry.