Plants that remain green through winter provide a rich visual element in the bleak shades-of-gray landscape. Dense green trees and shrubs also provide protective habitat for birds and other creatures, as well as a contrasting background for bright red or yellow twigged, bare-stemmed winter shrubbery. Winter greenery starts with evergreen conifers but includes broad-leafed shrubs and an array of hardy perennial plants, depending on your winter climate.
Trees which remain green anchor the visual landscape in winter, provide dark masses that seem to retreat in falling snow, and a deep background for contrasting gray and white twigs from bare deciduous shrubs. In the northernmost climes, pines (Pinus spp.), spruce (Picea spp.), fir (Abies spp.), Douglas fir (Pseudosuga Menziesi) and hemlock (Tsuga canadensis) all thrive. There are different species, varieties and cultivars of each of these to fit any northern winter landscaping need. Their needles vary in shade from darkest green to grey-blue, and available sizes and habits run from low-growing shrubs to towering trees.
In zone 5 and southward, holly (Ilex spp.) grows as a glossy-leaved evergreen, available in numerous species from shrubs to the American holly which reaches 50 feet tall. South from zone six, the Southern magnolia (Magnolia grandiflora) and Live Oak (Quercus virginia) add their magnificent forms to the green winter landscape.
In the coldest winter climates, Arbor vitae, juniper (Juniperus spp.), cedar (Cedrus spp.) and shrub forms of the northern conifer trees provide green shrubbery all winter. In zone 5 and lower, the shrub form of holly (Ilex spp.) including the glossy-leaved inkberry (Ilex glabra), provide dense masses of green leaves, while the Wintergreen barberry (Barberris julianae), Leatherleaf viburnum (Viburnum rhytidophyllum), mountain laurel, azaleas and rhododendrons (Rhododendron spp.) hang on to their leathery leaves all winter but grow in a more open habit, suitable for hanging small feeders to watch the hungry winter birds.
In zones 6 and southward, cypress (Cupressus spp.), Abelia (Abelia grandiflora) and boxwood (Buxus spp.), all remain green through the winter, and are often trimmed into geometric shapes which can be quite dramatic in the bare landscape, and even more so when topped with snowfall. The yucca (Yucca spp.) also keeps its green, spiky form through the winter in dry areas of zone 6 and south. South of zone 7, most species remain green through the winter as a hard freeze is uncommon.
Groundcovers and Small Plants
There are varieties of the creeping evergreens and small woodland evergreen plants suitable for all hardiness zones, including: euonymous (Euonymous spp.---there are also shrub varieties), English ivy (Hedera helix), periwinkle (Vinca minor), Oregon grape holly (Mehonia aquifolium), Creeping Mehonia (Mehonia repens) and bearberry (Arctostaphylos uva-ursi).
Plants like helleborus (Helleborus spp.) and ferns (numerous families and genera) stay green all winter even under snow, providing a welcome visual relief during January thaw and a good foil for the earliest spring flowering bulbs.