Though winter is often associated with darkness, animals entering a period of hibernation, and temperatures that are too cold for most plant life, it need not be devoid of seasonal color and flare. Some plants are naturally able to persist through these cool months without dying back or losing their foliage. Moreover, a handful of exceptional temperate species actually wait for a shorter photoperiod and significant drops in temperature to produce their winter blooms!
Perennials or winter annuals that set out blooms, retain their tough foliage, produce cool-season berries, or have lasting stems with ornamental appeal may just be the tickets to maintaining a vibrant garden all through the year. Some of these are small enough to thrive in a window box, where they can be combined with other plants to create a lively and colorful arrangement.
Your selection of plants and where you situate your window box would depend on the amount of sunlight, wind exposure, snow, and the incidence of frosts around your area. Some window boxes are best propped up beneath the protection of eaves or along a roofed porch, where they need not be fully exposed to the elements. Other arrangements with hardy vines and time-tested evergreens may be sturdy enough to withstand icy rain and direct winter sun!
1) English ivy (Hedera helix)
Well-loved for its evergreen foliage and the textural coverage it provides, English ivy is a phenomenal vine. With its reputation for thriving almost anywhere, it has proven to be one of the hardiest and most versatile plants around. Fast-growing and ever-lengthening, its stems can creep to heights of about 30 meters (98 feet) due to their incredibly strong aerial rootlets. Fortunately, these can be cut back frequently to encourage the vine to keep a more compact and well-maintained shape.
English ivy and its many eye-catching cultivars are fine choices for winter boxes because their foliage can withstand cool temperatures. Hardy to USDA zones 5 – 11, the foliage of some cold-hardy cultivars can be used to add visual interest in northern landscapes, where temperatures may drop down to around -10˚F (-23˚C). Cuttings of stems can be placed along the edges of a winter basket, where they may be trained to serve as “spillers” around an upright arrangement of winter plants.
2) Flowering cabbage (Brassica oleracea)
“Flowering” cabbage is often grown for its frost-tolerant foliage, which comes in vibrant shades of green, purple, grey, and white. These are perfect for injecting color and liveliness into the winter landscape as their crisp leaves look great in containers, dedicated beds, and plots. Ideal for adequately sized window boxes, most cultivars tend to grow to a mature height of around 10 – 15 inches (25 – 38 cm). Their rosettes can maintain a similar spread.
Typically grown as an annual, the flowering cabbage requires cool conditions to thrive. Once temperatures change significantly, its leaves undergo a phenomenon called “bolting”. In spring, they turn yellowish and may begin to die back. Best situated in light shade, the leaves can retain their visual interest in USDA zones 2 – 11, but they require mild winters to be able to persist throughout the entire season. Their colors tend to darken or intensify as temperatures drop (i.e., down to a minimum of around 5˚F or -15˚C).
3) Rosemary (Salvia rosmarinus)
A multipurpose, evergreen perennial that lasts through winter, rosemary is a remarkably rewarding herb to cultivate directly in the garden or within containers and window boxes. This flowering plant is set apart by its narrow, leathery foliage, which is infused with an incredible array of scented phytochemicals. While these are fantastic components of anyone’s culinary arsenal, they also make for a great pest repellent outdoors.
Hardy to USDA zones 7 – 10, rosemary can tolerate winter temperatures that dip down to around 15 – 23˚F (-9 to -5˚C). It is thus suitable for window containers in zones with mild climate conditions or relatively frost-free winters. In cooler areas, it should be overwintered indoors. Regardless, there’s no harm in testing its tolerance for conditions in your area; its perennial sprigs may thrive as far north as hardiness zone 6 if they are well-established and protected.
4) Winter-flowering pansies (Viola hiemalis)
Winter-flowering pansies, also known as ice pansies, are some of the most charming flowering plants for a container garden or window box. These cool-season plants are distinguished by their preference for low temperatures. In fact, warm winter conditions, with temperatures measuring 60˚F (15.6˚C) and up, may be detrimental to their survival. They are best suited for zones with wintertime soil temperatures around 45˚F (7˚C).
Those situated in window boxes can be afforded protection from strong winds, rain, and snow, allowing their buds and blooms to continue developing through the season. Typically graced with multi-colored petals, winter-flowering pansies boast shades of red, pink, yellow, purple, and white. In plant nurseries, they may be grouped into varieties under V. tricolor or Viola x wittrockiana. Those planted in fall may have multiple bloom periods lasting into early spring, mild conditions permitting.
5) Ivy-leaved cyclamen (Cyclamen hederifolium)
The icy-leaved cyclamen is perhaps one of the cold-hardiest members of its genus. This remarkable flowering plant is hardy to USDA zones 5 – 9, where it can withstand temperatures down to -4˚F (-20˚C) in winter. An unsurprising recipient of the RHS Award of Garden Merit, it makes for a stunning addition to window boxes, from which its upright tufts of butterfly-like blooms can combat the chilly and drab atmosphere of the darkest months of the year.
A rosette of ivy-leaved cyclamen grows to a full height of about 6 inches (15 cm) and an easily manageable width of about 6 – 12 inches (15 – 30 cm). Its small size makes it ideal for various sizes of window boxes, where it can be grown on its own or surrounded by an array of other cold-tolerant plants. Its foliage, which develops during or after the appearance of its blooms, is variegated and shaped like ivy. Evergreen, it can be used as textural ground cover from fall to spring; winter is actually its peak season for growth.
6) ‘Winter Gem’ boxwood (Buxus microphylla var. japonica)
The ‘Winter Gem’ variety of B. microphylla is a fantastic dwarf boxwood for container gardens, pots, or window boxes. This evergreen shrub is one of the most reliable options for winter, during which its foliage should continue to stay green, highly textural, and firmly secure on their stems in temperatures down to -20˚F (-29˚C). Hardy to USDA zones 5 – 9, its leaves may tolerate brief frosts but should look their best when they are afforded protection from harsh winds.
This boxwood can grow to about 4 feet (1.2 meters) tall if it is rooted into well-draining substrates and situated under full to partial sun. If it is grown out of a window box, it should respond well to being pruned in a square or rounded shape. Compact, its new stems should give it an increasingly dense and structured appearance – one which can be used as a natural, low-growing screen for your windows all throughout the year.
7) Winter-flowering heather (Erica carnea)
As the winter-flowering heather grows to a full height of just 6 – 12 inches (15 – 30 cm), it is perfectly suited to the confines of a small to medium window box. This stunning evergreen subshrub comes in more than 100 radiant cultivars, so several of these can be grown next to one another to create an array of colors. Imagine peering out of an initially gloomy window, only to be greeted by the most delicate tufts of cool-season blooms!
Bell-shaped heather blooms arise in dense racemes that significantly change the appearance of their leafy stems. They may be abundant enough to almost entirely mask all of the plant’s tiny, needle-like foliage. Those of some cultivars appear through early to late winter, serving as reliable sources of nectar for winter bees that venture out on mild days.
8) Monkey grass (Liriope spp.)
Monkey grass, also known as lilyturf, is an impressively hardy member of the Asparagaceae family. For this reason, it is often used as a textural plant in temperate gardens and landscapes. Its spritely foliage also looks fantastic as an ornamental addition to containers and window boxes, where it can easily be grown to hide edges or to complement the visual appeal of more delicate perennials. Though its clumping form (L. muscari) can spread on its own via networks of underground runners, it is not known for being particularly invasive.
Hardy to USDA zones 5 – 10, monkey grass fares well through mild winters. It may enter a period of dormancy once its roots and leaves are exposed to low temperatures (down to 14˚F or -10˚C), but this should not significantly impact its appearance. Though its leaves may stop growing, they’ll continue to add fine texture and color to their containers. Note that even well-established specimens will not tolerate either frosts or intense heat very well.
9) American wintergreen (Gaultheria procumbens)
One of the more quirky options for a winter window box, the American wintergreen greets the chilliest of months by producing its eye-catching bunches of red berries. These are contrasted by a backdrop of leathery, evergreen leaves, which may develop subtle red tinges as temperatures drop. The blooms of this species, which are pinkish or starkly white in comparison, appear as early as summer. Bell-shaped, these are produced in groups of three and arise from the stems’ leaf axils.
As the American wintergreen is hardy to USDA zones 3 – 9, it is known for being a potential source of food for winter wildlife. If you cultivate an open garden, a thriving specimen of this shrub may have deer or other small mammals creep toward your window boxes once other perennials become devoid of their leaves! You might even find yourself opening your frosty windows to pick at the fragrant leaves, which emit a scent that is reminiscent of peppermint.
10) Dwarf Japanese garden juniper (Juniperus procumbens ‘Nana’)
Evergreen conifers can be used as accent plants in winter window boxes too! Of course, due to the limited amount of space, either their dwarf varieties or their cuttings are preferred. The ‘Nana’ form of the dwarf juniper is one fine option due to its naturally petite size and the adaptiveness of its roots to restricted spaces. Occasionally grown as a bonsai tree or as a sprawling, ground cover shrub for raised plots or container gardens, it sends out compact and readily intertwining branches.
This low-growing, conifer cultivar grows to about a foot tall at most. Its needle-shaped foliage is bluish-green and is arranged in whorls with three leaves each. In winter, the evergreen foliage can take on a slightly purplish color in response to the cool temperatures. Slow-growing, they are retained by their branches throughout the year in USDA hardiness zones 4 – 9, where winter temperatures may dip to around -20˚F (-29˚C).
11) Fortune’s spindle (Euonymus fortunei)
Though the fortune’s spindle is capable of thriving not only in temperate but also in tropical regions, this shrub can remain evergreen in winter conditions. Occasionally grown as a climbing plant due to its tendency to elongate in a vine-like manner when provided with enough support, it is also known as the “wintercreeper”. If you intend to grow this species out of a window box, you may either cultivate its stands as a central, upright feature or as trailing plants that are trained to grow around the window itself.
Fortune’s spindle comes in several eye-catching cultivars with a tolerance for temperatures down to 10˚F (-12˚C). Those with variegated leaves tend to have a slower spread rate, so they are usually recommended if you reside outside of this species’ native range. These are also less likely to compete with other winter plants in window boxes. As well-established specimens tolerate heavy shade, they are suitable for north-facing zones or for windows that are shaded by an eave.
12) Japanese skimmia (Skimmia japonica)
Another Asian native that flaunts its ornamental features through the winter months, the Japanese skimmia is often cultivated as a specimen shrub or as a bonsai plant. Known for its tolerance of frosts, it can easily thrive in temperatures that dip down to around 5˚F (-15˚C). Hardy to USDA zones 6 – 8, it is recommended for winter window boxes in regions with mild to moderate climate conditions. Its lovely display of winter fruits is particularly vibrant in areas receiving partial to full shade.
This shrub’s clusters of bright red berries are contrasted by its distinctly leathery, smooth-margined, and lance-shaped leaves. Evergreen, these arise in whorled clusters along the tips of elongating stems. Collectively, the stems create mounds that may measure up to 4 feet (1.2 meters) tall when they are rooted directly into the garden. Those in window boxes are more likely to maintain a manageable size. The cultivars ‘Rubella’, ‘Obsession’, ‘Temptation’, and ‘Fragrant Cloud’ are best for winter appeal.
