Window boxes are charming miniature gardens with all the same horticultural potential of a big flowerbed in the ground. Because the scale is limited, you'll need to concentrate on smaller plants, but you don't have to compromise on style.
When you're planning a window box -- or a series of them for the front of a house, a balcony railing or a terrace wall -- think creatively. You could fill a box with bright red geraniums, of course, but this is a fine opportunity to explore other options at little cost. Succulents, ornamental grasses, perennial plants and small shrubs are all great candidates for window boxes. Tropical plants, such as caladiums, small palms or bromeliads, are excellent choices, too. They will flourish through a long, hot summer without pampering.
But your first choice has to be about the box itself. Garden shops and big-box stores sell window boxes in standard sizes to fit most windowsills. Hayrack-style planters, lined with coco-fiber inserts that hold the soil in place, are also widely available. If you can't find a planter that quite fits your situation and suits your style, easy do-it-yourself plans, adaptable to windows of every size, are available on the internet.
There's no need to splurge on an elaborate container: Simple boxes may be best because the plants are the real stars of a window box. You may need to install brackets (available at garden shops and building-supply shops) to support the container. Whatever container you choose, it should have drainage holes.
Before you shop for plants, consider the conditions where your window box will be mounted. You'll need sun-loving plants for south-facing windows, and plants that flourish in shade for windows facing north. Most plants will thrive in spots that receive good morning (eastern) light. Afternoon (western) exposures can be a little hot and harsh, so if your windows face west, look for plants that can take the heat.
Your own garden can be the inspiration for window box plantings. Ideas that work in the ground will usually work well in planters, too, on a smaller scale. Go ahead and try your favorite plants in your window boxes -- there's nothing wrong with more of a good thing. You may want to echo the colors and textures in your garden, or complement them with different tones and shapes.
At your local garden shop, remember to think about all the options. Many people tend to rely on annual flowers for window boxes, but shrubs and perennial plants will make a window box planting more interesting than an all-annual design. They broaden your palette. Small shrubs, such as boxwoods or dwarf conifers, will give your window box garden a fine foundation. Take a look at miniature roses and even small hydrangeas. Plants in one-gallon pots might be just right: You want plants that are large enough to show up right away and get your little garden in the window off to a strong start.
Low-growing ornamental grasses, such as Mexican feather grass (Stipa tenuissima), dwarf Japanese bloodgrass, short fescues or little fountain grasses, which have bottlebrush-like blooms, will fill in around flowers. Hostas, especially those with a creamy stripe or other variegation, will look far more distinguished in a shady exposure than a window box full of the usual impatiens. Try combining coral bells, hellebores, salvias or succulents with window box favorites, such as begonias and ferns.
Trailing plants will add to the fullness of your design, but choose carefully. Ornamental sweet-potato vines will require regular trimming through the summer. Cascading petunias or million bells (Calibrachoa), which has many small flowers that look like petunias, might be a better choice. Bacopa, lobelia and even ivy all trail gracefully.
Just like a garden in the ground, your window box can change through the seasons. You might start the spring with a few daffodils and tulips from a garden shop, then replace them with sunny annual flowers or herbs after the weather warms up and the bulb flowers fade. In midsummer, you can brighten up the palette with new blooms; and in fall, you could find a spot in your window box for mums and asters, or add edibles such as Swiss chard, mustard and kale. Don't worry about disturbing existing plants; everything will settle down as soon as you water. On the other hand, if a plant is getting tired, get rid of it -- and the sooner, the better.
Window boxes are the perfect size for new gardeners who are not yet quite ready to commit themselves to a big undertaking. They're also a great way for experienced gardeners to try out new ideas. For renters, they are an easy and obvious choice. You don't even need a window: boxes fit on a balcony or deck rail, and they're pretty on a porch or patio. And now is the time to plant them, for a miniature garden you'll be able to enjoy all season.