Winter-blooming plants are rare and precious. In moderate climates, Zones 6 and south, a variety of small plants and shrubs bloom outdoors year-round. In Zones 5 and northward, few plants bloom outdoors in the darkest weeks of winter, but late-fall and earliest-spring flowering varieties minimize the seasonal blooming gap. Indoor-blooming plants can brighten the winter at home or at the office in any growing climate.
The common witch hazel (Hamamelis virginiana) sold as nursery stock is usually labeled as hardy to zone 5, but specimens grow wild in New England to zone 3, so obtain locally field-grown specimens for maximum hardiness in the coldest areas. Different local strains of witch hazel bloom at different times, from November to February, sporting fireworklike bursts of yellow, orange or red flowers with the distinctive witch hazel smell.
Winter-flowering heather (Erica carnea) is also hardy to Zone 4 or farther north, and comes in a variety of white, pink and lavender blossom shades. The Russian olive tree (Elaeagnus) blooms in late autumn to early winter to zone 5, but is prohibited from planting in many areas due to its invasive nature.
In Zone 6 and further south, a number of shrubs come into bloom sometime between November and early March, including fragrant wintersweet tree (Chimonanthus praecox), winter-flowering viburnum (Viburnum X budnantense 'Dawn' or 'Pink Dawn'), Korean forsythia (Forsythia ovata), Chinese Daphne (Daphne odorata) and the Christmas box (Sarcococca hookeriana 'Digyna').
In zone 5 and northward, winter pansies (sold under a variety of trademarked names) are the only small flowers that bloom through the darkest winter months, though flowering kales and cabbages provide a colorful substitution for actual blooms in winter windowboxes and patio planters. Broccoli raab--a turnip green grown for its broccolilike edible shoots--is winter-hardy and will send forth small, airy sprays of yellow flowers year-round.
In these colder climates, late-autumn blooms extend into the early winter, including late fall sedum, monkshood, toad lilies, asters and football mums. The earliest spring bulbs begin poking through the snow in February, about 3 months after the last fall flowers succumb to winter. These include snowdrops, scilla, snow crocus and snow glories.
In more moderate climates, ranunculus and the pincushion flower (Scabiosa) will bloom all year, while the earliest spring bulbs will emerge in late winter.
Many plants will bloom indoors during winter under proper growing conditions. The Christmas cactus and Amaryllis are common holiday-season blooms. Many of the spring-flowering bulbs--narcissus, hyacinths, crocus--can be forced to winter bloom by first subjecting them to a freeze, then planting them in pebbles and water in a warm, sunny indoor location. Small forsythia, pussy willow or azalea shrubs can be brought indoors in containers for late-winter bloom.
Early-spring blooming English primroses will bloom in pots indoors all winter. Miniature roses and exotic orchid varieties will bloom indoors in winter under artificial lights and with careful attention to cultivation requirements.