No matter what season, there are a few things you can do to make sure your container plants are happy:
Drainage hole: All containers, including window boxes, must have drainage holes. If they don't, you need to drill them.
Width and Depth: The width of your window box should match your window. The depth of the box should be 6 to 8 inches -- deep enough for plants to set root.
Soil: Use a lightweight potting mix. Never use soil from your yard because it's too heavy for use in a container.
Let's get planting!
Fill the window box about two-thirds full with soil. (Optional: some people line the box with several pieces of newspaper to act as a blotter.)
Next, add a structural element that will stay in the window box all year, such as a shrub or small tree. Alberta spruce, a small arborvitae, or boxwood offer evergreen color all year round.
Now add seasonal flowers. Pansies an take a cold nip, so they're perfect for spring window boxes. Perennial herbs such as parsley and sage are excellent choices, too.
When summer arrives, the heat will wilt the pansies, so replace them with sun-loving annuals. Supertunias are ideal because they cascade over the sides. And they grow like crazy in summer's hot weather. Geraniums also love the heat -- and offer huge flower clusters.
In autumn, replace summer annuals with fall flowers. Asters bloom in shades of purple, lilac, blue and white. And mums are a traditional fall favorite. Your window box has a fresh fall feel -- with just a few plant change-outs.
When freezing weather arrives, remove all the plants except the shrubs. Add holiday greens such as pine boughs or holly berries. And stick in ornaments such as wire stars to decorate your winter view until spring rolls around again.
A window box for every season is easy when you start out with some stay-all-year structure and switch out companion plantings as the seasons progress. You'll have an ever-changing view year round.