When my windows are open, incoming breezes are scented by sun-warmed lemon verbena, cinnamon basil, and sweet heliotrope growing in the window boxes. The herbs are close at hand where I like them, the leaves and flowers handy for cooking and useful for echoing interior color schemes. From the outside, the flower boxes that frame our windows lend a friendly, inviting look to the house.
Window boxes can enliven the front of a big-city brownstone, a suburban ranch house, or a farmhouse set amid rolling fields. They don’t even have to sit on windowsills. Whether hanging from the balcony of an apartment or over a deck railing, framing a broad veranda, mounted on a plain stretch of wall, set atop a stone fence, or resting on a bench or picnic table, the elongated planter is a graceful accent.
Each window box can be a small garden composition with its own structure, balance, and stimulating combinations of color, texture, and form. Bright annual flowers need not dominate; combinations of herbs with interesting, contrasting foliage are long-lasting, fragrant, and useful. Most window-box plantings are intended to be temporary, to be enjoyed through the warm months but outgrown by season’s end, giving us the opportunity to try something new the following year.
Even beginning herb gardeners can have imaginative window boxes full of healthy herbs. The right container, a good potting mix, and diligent watering are the secret to bountiful, fragrant boxes.
Pick a Box
Window boxes look best when they reflect their architectural surroundings. I chose stained cedar for the front of the house to match the siding and weathered pressure-treated pine boxes for my deck. Other rot-resistant woods include cypress and redwood. You can leave wooden boxes to weather or paint them to match the house or trim color. Plastic, fiberboard, or metal liners (with plenty of drainage holes) can extend their life.
Ready-made plastic or fiberglass boxes are available in many sizes to fit a variety of windows or other situations. I’ve seen plastic boxes that fit over deck railings like saddlebags. Most plastic and fiberglass boxes are lightweight and can withstand extremes of heat and cold without cracking. They are available in colors such as white, black, dark green, terra-cotta, gray, and granite to blend with any decor. A white plastic box might be conspicuous in a garden, but it is unobtrusive when placed on a white-painted windowsill. My friend Becky has a collection of beautiful terra-cotta planters on her deck, some adorned with swags and angels, but among the genuine pottery containers are several inexpensive, terra-cotta-colored plastic window boxes overflowing with flowers and herbs. No one notices that they aren’t pottery.
Window boxes made of wire or wrought-iron rods are another alternative. Some have a plastic coating for rust resistance and easy cleaning. Liners of fiberboard or long-fibered sphagnum moss increase moisture retention and insulation from temperature extremes while they keep the potting mix in place.
Whatever type of window box you settle on, good drainage is essential. If your plastic window boxes don’t have ample holes, enlarge them or drill more; inadequate drainage is seldom a problem with wooden or wrought-iron boxes.
You can either plant the herbs directly into a box filled with potting mix or, to lighten the load, put them in individual pots, which can be replaced if the plants get too big or begin to decline. I tuck moist sphagnum moss around the pots to disguise the rims and keep them from drying out. One of my favorite boxes holds five one-gallon pots snugly and has open ends so I can slide them in or out.
Mounting the Box
A window box filled with potting mix and plants is heavy, especially after watering. Attach it securely to the window or other framework with rustproof (brass or galvanized) screws or to the outside of the house immediately below the window with brackets. Plain right-angle brackets are functional, but ornamental ones are especially nice for upper-story boxes that can be seen from below. Space brackets 3 or 4 inches in from the ends of the box, with additional brackets every 12 inches or so. Use two or more boxes to span the width of a large window. Railing brackets are available to secure window boxes to deck or balcony handrails.
Window boxes should drain freely—and away from the house. To prevent a permanently damp spot on the siding, use cork spacers to hold the box away from the wall and encourage air circulation. If you’re using brackets, just leave a little space between the box and the house.
Many kinds of herbs can be used in window gardens, provided that they have suitable growing conditions. Sun, wind, and reflected heat are drying; fluctuating moisture levels and a confined root zone—conditions present in any container garden—contribute additional stress. The list at left suggests plants suited to sunny and shady exposures.
On the shady north side of my house, I grow bay, burnet, parsley, and sweet cicely. In south-facing window boxes, which receive sun all day, thyme, oregano, santolina, and miniature roses do well.
Consider how plants will look against the color of the house and trim. Many color schemes, including the mauves and blues so common among herbal flowers, work well with my informal, light brown cedar siding or other neutrals such as white or light gray.
In areas colder than Zone 7, don’t count on perennials reliably surviving winter in a window box. You may overwinter the plants in a cold frame, greenhouse, or enclosed sunporch, or simply compost them and start over next spring.
Here in Atlanta (Zone 7), many herbs and other ornamental plants will overwinter even in containers, but I choose plants hardy to slightly colder zones to minimize the chance of casualities. October-planted hardy annuals or biennials such as parsley, cilantro, calendulas, pansies, Johnny-jump-ups, and hardy snapdragons thrive all winter in my window boxes. Small bulbs such as crocuses, snowdrops, miniature daffodils, and anemones tucked around the herbs add color when they bloom in late winter and early spring, but I remove them after they finish blooming to give the herbs more room to grow. Sweet marjoram, oregano, mint, and lemon balm plants go dormant and disappear during the winter, but rosemary, lavender, upright thymes, santolina, dwarf English boxwood, germander, and dwarf yaupon holly keep their foliage all winter and can even be decorated for the holidays. They also look terrific shaped into topiary. In late winter, I supplement these evergreen herbs with blooming Lenten roses, heathers, or spring bulbs, which I replace with tender annuals and brilliant tropicals after the danger of frost is past.
I sometimes maintain a given color scheme in my window boxes through the seasons with a succession of plantings. For a yellow-and-lavender combination, I might begin the year with blue pansies, parsley, golden lemon thyme, dwarf yellow snapdragons, and miniature daffodils. In summer, I plant Persian catnip, sage, dill, and yellow nasturtiums and then finish with fall-blooming Mexican tarragon and velvet sage. One year, feeling daring, I combined red Salvia greggii, cinnamon basil, ‘Purple Ruffles’ basil, maroon perilla, red pentas, and trailing black peppermint with upright lemongrass, which becomes red-streaked in the fall.
The simplest arrangement is a window box filled with a single herb, perhaps bright nasturtiums or fragrant heliotropes, but sometimes I like to cram as many different kinds of plants as I can into one box. I’ve found that familiar window-box combinations such as red geraniums, white petunias, and ivy are enriched by adding herbs in similar colors—in this case, white-flowered feverfew and bright green parsley. Favorite plant or color combinations may be repeated in nearby containers or expanded in garden beds beneath the window boxes if space permits.
Planting and Nurturing
When planting herbs directly in a window box, I first fill it halfway with a moistened potting mix containing peat moss and vermiculite to retain moisture, perlite to improve drainage, a little lime to neutralize the acidity of the peat, and a wetting agent. I also add a water-absorbing polymer to cut down on watering, but I use a light hand. Once I added too much, and my window box looked as though it was oozing gelatin all summer. The addition of cottonseed meal or other fertilizer ensures that the plants get off to a good start.
After placing small potted herbs or rooted cuttings in a pleasing design, keeping in mind their growth habits and mature sizes, I transplant them into the box. I add potting soil up to 2 inches below the rim of the box, tamp it firmly, and water everything thoroughly.
Window boxes, especially those with a sunny exposure, need daily attention and generous watering. The plants, dependent on the gardener for all their needs, require a steady supply of nutrients. I use a quarter-strength solution of liquid houseplant fertilizer every time I water. You can also use a weak solution of manure tea, but then you might want to close your windows for a little while.
Just after planting, I pinch off the growing tips of each plant to encourage bushy growth. Harvesting herbs regularly has the same effect. Whenever I need a sprig or two, I clip back to an outward-facing bud or to just above a set of leaves.
The herbs also benefit from regular grooming. Pinching off dead flowers prevents plants from setting seed and stimulates the initiation of new flower buds. Removing yellowing leaves and bent or broken branches discourages the growth of disease organisms.
Pests aren’t ordinarily a problem, but if you notice leaf drop when the plants seem otherwise healthy, check for aphids, scale insects, whiteflies, or spider mites. A daily spray of water can reduce the incidence of spider mites, which like hot, dry conditions. If plain water or hand-picking the pests doesn’t do the trick, use an insecticidal soap such as Safer’s, or try inert horticultural oils on smooth-leaved herbs. Follow label directions.
Author and lecturer Geri Laufer tends a large garden and many window boxes at her home in Atlanta, Georgia.