The most winter hardy plants are usually plants with woody stems. These plants resist the seasonal effects of freezing weather. The risk of winter damage is greatest during the fall and spring when the plants are not completely dormant. Spreading mulch 2 to 2 1/2 inches deep around the plant after the soil has frozen helps to protects winter hardy plants. This prevents the ground from warming up too early and causing premature spring growth that runs the risk of frost damage. Use shredded bark, wood chips, compost, peat moss, pine needles, straw and hay as your winter mulch.
American bittersweet (Celastrus scandens) grows as a 60 foot vine. The leaves are oblong with delicate serrated edges and pointed tips. It produces small, green flowers followed by shiny orange or red fruit that splits open when ripe. Wild birds, attracted to the fruit, flock to this vine . American bittersweet is commonly used as an ornamental plant. American bittersweet is winter hardy to USDA zone 2 which has temperatures down to -50 degrees Fahrenheit.
Bearberry (Arctostaphylos uva-ursi) is a slow growing evergreen that reaches 6 to 12 inches tall. This groundcover has shiny, dark green leaves that are 1/2 to 1 inch long. The leaves turn bronze or reddish in winter weather. Bell-shaped, white and pink blossoms appear in April and May. Small, bright red berries show up in the late summer. Bearberry is salt tolerant and can withstand coastal conditions. Bearberry is hardy to USDA zone 3 which has low temperatures of -40 degrees Fahrenheit.
Common lilac (Syringa vulgaris) has heart-shaped, 2- to 4-inch-long leaves that are dark green to bluish green in color. The undersides of the leaves are a paler color than the tops. This large shrub produces clusters of lavender, pink and white flowers on the ends of the branches in late spring. Common lilac grows 15 feet in height and creates several suckers from the roots each season. Common lilac is hardy to USDA zone 3, which includes International Falls, Minnesota and St. Michael, Alaska.
Rugosa rose (Rosa rugosa) grows 4 to 6 feet tall in a dense, round shape. This small deciduous shrub produces upright stems with dark green leaves made up of five to nine leaflets. Fragrant, 2 1/- to 3 1/2-inch flowers bloom all summer long in rose and white colors. In the fall, rugosa rose grows 1 inch, red rose hips. Rugosa rose survives in USDA zone 2 in places like Unalakleet, Alaska and Pinecreek, Minnesota.
Sweet fern (Comptonia peregrine) is a slow growing deciduous dwarf shrub reaching 2 to 4 feet tall. Slender branches spread 4 to 8 feet wide. Narrow, fern-like leaves are dark green turning greenish-brown in the fall. Sweet fern produces a small, yellow-green blossom in the spring. Sweet fern lives through winters in USDA zone 2 that include places like Manitoba, Canada and Prudhoe Bay, Alaska.
Virginia creeper (Parthenocissus quinquefolia) grows compound leaves with five leaflets reaching 4 to 8 inches across. The shiny green leaves on this vine have serrated edges. In the summer, small green flowers cluster together. Blue-black berries 1/4 inch across grow and mature in the late summer. This climbing vine provides a quick growing ground cover or privacy screen. Virginia creeper is winter hardy in USDA zone 4 that has temperatures as low as -30 degrees Fahrenheit. and includes Minneapolis, Minnesota and Lewistown, Montana.