How to create a decorative accent throughout the seasons—and increase your curb appeal.

Old Fashioned Charm in Modern Gardening

There’s something charming about window boxes, whether mounted traditionally beneath windows, on a deck railing or simply set on a step or near a garden. For many people, especially those with little or no yard—or little or no time for more intensive gardening—window boxes are a perfect way to exercise their green thumb. For others, they’re an extension of their gardens, and a way to have ever-changing displays throughout the seasons.

As with any type of gardening, there are a few logistics to consider before you begin. First of all, are you going to mount your boxes under your windows, or on a deck or veranda railing? Make sure that whatever brackets you purchase or make to support the boxes are strong; your containers may not be heavy when empty, but once you plant them or arrange boughs and branches in them they’ll weigh significantly more.

Worried about water draining from your window boxes rotting the wood on your shingles? Putting liners in your boxes easily rectifies this. Or if you’re building your own window box, it’s a good idea to buy a plastic planter and build your box so the planter can sit inside it (many plastic planters come with trays built in). For an easy-to-build planter box see “A Place in the Sun,” on page 87.

Planting Recommendations

What sort of potting medium should you use? It's best to get a growing mix suitable for containerized plantings. Resist the urge to use soil out of the garden—you’ll regret it later. Not only will it be full of weed seeds and possibly fungal and bacterial diseases, it will be much heavier than commercial potting media. Most commercial mixes are a blend of peat moss, perlite and vermiculite, which allows for good drainage and aeration. Some now come with slow-release fertilizer included, or with tiny crystals of moisture-retaining compounds to keep the soil moist between waterings.

You can purchase several moisture-retaining products at garden centres, but follow instructions carefully when mixing them into your potting soil. One gardener I know made the mistake of using a teaspoonful of Soil-Moist, a clear moisture-holding product, in a small window box. When this much compound has water added to it, it swells up to fill a three-quart bowl. A heavy rain came along, and the gardener found himself with a strange concoction bubbling out of his container—as the moisture-holding compound swelled up and overflowed, it took the soil and plants with it. It’s a mistake to think that if some is good, more is better.

If your window boxes have built-in drainage holes, use a strip of window screen or other fine mesh to line the bottom, so your potting medium doesn’t wash out. Before planting, mount the box to make sure it fits properly. In fact it may be easier to plant or decorate the box already mounted—it’ll be heavy to lift afterwards but also you can stand back and see how the composition suits its setting as it’s taking shape.

Ensure your planting medium is damp but not soggy, so you don’t have to deal with dust while you’re tucking your plants in, and they’ll have a welcoming environment in which to get started.

As with any containerized planting, window box plantings will benefit from a regular application of water-soluble fertilizer. I use liquid seaweed emulsion, applied once weekly when watering. It’s a gentle solution that adds small amounts of the required nutrients, keeping plants looking great and flowering robustly throughout the season. If you’re using chemical (non-organic) fertilizers, use only half the amount called for in the instructions—this will reduce excess fertilizer salt buildup in your boxes, yet still give your plants a boost.

Planting by theme

What you choose to plant in your window boxes season by season depends of course on your own preferences for colour, texture, flowering time, etc. However, there are a few rules to follow to ensure success. Don’t set plants too deeply in the soil; stems shouldn’t be deeper than they had been in their pots when you bought them.

While we’re often told to leave ample spacing between plants for them to grow, in a container planting you can get away with planting more closely than you would in a garden bed. Unless your aim is to create a Zen or minimalist style, you want the boxes to be lush and abundant, spilling over with foliage and colour.

Want to do a culinary window box? Simply plant it with your favourite cooking herbs such as basil, oregano, chives, parsley, rosemary and sage. Include a few transplants of brightly coloured lettuces or other greens, keeping them regularly harvested so they keep producing new growth. For accent, include edible flowered annuals such as calendula, Johnny-jump-ups and scented geraniums. This is a great planting to have on your kitchen window or a nearby deck, so you don't have far to go for a few sprigs of herbs or a handful of greens.

How about a fragrant window box, so you have waves of scent wafting in your windows? Choose scented annuals such as stocks, phlox, heliotrope and the species types of nicotiana (as opposed to the hybrids, which have great colour but less scent). Herbs such as scented geraniums, lemon verbena and lavender also make great additions to a scent box.

Longing to do something whimsical with your window box? Put a piece of rustic folk art on it as a focal point—a small wooden birdhouse, wooden cutouts of hearts or other motifs, twig wreaths…any of these can make a pleasant window box arrangement outstanding. Don’t be afraid to use faux materials, such as artificial fruits and flowers; the secret is to buy good quality reproductions, and use them sparingly.

Lest you think we have only one (short) season here in the Atlantic Provinces, think again. The following ideas will help you reinvent your window boxes, throughout all seasons.

Fulsome Fall

By mid September I’m bored with our container plantings—I’m ready to turf out the nearly-spent annuals and replace them with offerings to celebrate this time of plenty in the natural world.

Autumn means chrysanthemums at garden centres, and while some may find them cliché, I think they’re a dandy way to celebrate the season’s abundance. Growers are planting them in large (10 to 14 inch) containers so that instead of a few polka dots of colour there’s a mass of bloom in one shade for dramatic effect. You may find these large pots too big to transplant into window boxes, but there are always smaller pots of mums on sale for just such uses. Plant breeders are always coming up with terrific new colours too, so you can work with the usual autumn shades or punch up the mix with rich burgundies, hot fuchsia and even white.

Ornamental cabbage and kale are among my favourite choices for fall colour. The deep purples and roses contrast nicely with the usual autumn palette of golds, rusts, reds, bronzes and coppers. Ornamental kale reminds me of a huge rose bloom, and makes a terrific focal point in a planting. If you have large window boxes, you can create a dramatic effect by using just kales to fill the box; add stalks of ornamental grass and flowerheads for contrasts in texture, colour and shape.

Other good candidates for fall window boxes include the autumn-flowering succulents ‘Autumn Joy’ or ‘Voodoo’ sedum, heathers and other ericaceous plants, and fall-flowering grasses such as purple fountain grass. Rather than plant directly into soil, you can simply set plant pots down inside the window boxes. Remember to check plants in pots often to ensure they haven’t dried out.

If you plan to replace the soil in the window box for spring plantings, after the live display has run its course in fall take the soil out—or leave a couple of inches in the bottom to hold material for winter arrangements. Or use lava rocks or charcoal to hold your winter materials in place; they’re lightweight and allow water to drain away.

Materials to consider using:

•    Ornamental gourds and pumpkins
•    Vines and berries from bittersweet vine
•    Grape vines
•    Seed heads of perennials such as teasel, Queen Anne’s lace, coneflowers, poppies
•    Dried hot peppers
•    Indian corn
•    Everlasting flowers such as statice, Japanese lanterns, strawflowers, lunaria
•    Cuttings of wild bayberry (Myrica)
•    Wild cranberry vines (Vaccinium macrocarpon)
•    Branches of oak, maple, burning bush     and other brightly coloured fall foliage
•    Bows and decorative accents using raffia or wired ribbon

Wonderful Winter

While it’s true you won’t have many plants blooming outdoors in winter (not even icicle pansies, snowball bushes or snow peas), don’t despair—you can decorate your window boxes using foliage from evergreens, grasses, seed heads and other plant material, as well as lights and other decorations. The secret to success is to stuff the boxes full with evergreen branches and then add sprays or accents of other materials, which you can change as the season progresses. Including bows made from wired ribbon adds a festive look to your home’s exterior.

Materials to consider using:

•    Red osier dogwood twigs
•    Yellow-twigged dogwood
•    Lilac branches (their architectural twists make attractive accents)
•    Sumac (Rhus typhina) seed head spikes
•    Branches with red berries, such as Canada holly, English holly and multiflora rose
•    Rosehips from wild or rugosa roses
•    Prunings from evergreen shrubs, especially those with unique foliage colours, such as ‘Blue Star’ juniper, ‘Golden Plumosa’ false cypress, ‘Rheingold’ cedar
•    Evergreen cones, the bigger the better (if you don’t have a source nearby look for bags of cones at hobby or dollar stores)
•    Tendrils of bittersweet vine or other woody vine
 •   Curly willow branches
•    Heaths and heathers
•    Evergreen ivies (Hedera helix)
•    Clippings of boxwood, euonymous or other broadleaf evergreens

Sweet Spring

Those harbingers of spring gardens, the fall-planted bulbs, work well in window boxes. Some gardeners pot bulbs in the fall, store them in a cool place and bring them out in late winter or early spring to add to their window boxes. You can also usually buy pots of pre-chilled bulbs at nurseries in the spring, but often your selection is limited.

Small bulbs such as glory-of-the-snow (Chionodoxa), grape hyacinth (Muscari), scilla, snowdrops, puschkinia and winter aconite work well at the front of window boxes, especially with species tulips and miniature-flowered narcissus in the back.

If you have a profusion of evergreen periwinkle groundcover (Vinca), try digging some up and adding it to the box, allowing it to cascade down the front; the starry blue flowers are a nice complement to the fresh colours of spring bulbs. For structural contrast, clip a few branches of forsythia just as they come into bloom; tuck them into small glass jars sunk into the back of your window box. The bright gold blooms will add an extra burst of colour in early spring.

As with forcing bulbs in containers indoors, it’s unlikely that forced bulbs for window boxes will come back a second year. You can still give them a chance: remove the bulbs from your box when they’re finished flowering and plant them in your garden, allowing the foliage to die back to produce food for the bulb.

Soulful Summer

In summer there are a dizzying array of annuals, perennials, herbs, small shrubs, grasses and foliage plants to combine in an equally dizzying number of window box arrangements. Try using short annual or perennial grasses in plantings—some of the Carex species, blue fescue, blue oat grass, annual ornamental millets and bronze or leather leaf sedge.

Lantana is a unique perennial with multicoloured flowers, and while it has an unpleasant smell to people it’s irresistible to butterflies.

There are wonderful choices for foliage plants available today, including coleus, creeping Charlie, Swedish ivy and licorice plant, all in remarkable colours far different from those we remember from even 10 years ago. Some gardeners add foliage perennials to their summer plantings, including small hostas (try ‘Blue Cadet’, ‘Golden Tiara’, or some of the mini hostas such as ‘Pandora’s Box’, ‘Teaspoon’ and ‘Teeny Weenie Bikini’), coral bells (Heuchera hybrids) and dead nettles (Lamium and Lamiastrum species).

Every year the plant breeders roll out dozens of new annuals, with awesome bloom colours that give even old favourites a bright new look. While I wouldn’t plant a petunia for any reason, I love calibrachoas or million-bells, especially ones in fiery shades.

The best idea is to get to know a local garden centre operator; ask about new plants and try a few out. Last spring I discovered a small unique shrub from Australia called Silver Sand (Calocephalus). I planted this silver plant with black mondo grass (Opiophogon) and a vibrant Livingstone daisy in a small terra-cotta window box planter, and the result was dynamic.