Window boxes bring flowers and foliage to the forefront of a home's exterior design. These lovely boxes sit tucked under the windowsill, adding beauty to the outside of the house, as well as the inside. Designing a window planting box requires assessment of the lighting conditions in the location. Each plant must be chosen to match sunlight availability and thus ensure the health of the plant. Creating a design depends on the preferences of the gardener. The many varieties of annual plants allow a wealth of choices in color, texture, height and foliage.
Evaluate the sunlight availability in the planned location of the window box. This first decision refers to the amount of sun exposure plants can tolerate over the course of a day. Full sun means the area receives direct light for more than six hours and partial sun means it receives four to six hours each day. Partially shaded areas experience less than four hours of sun a day, and full shade areas receive no direct sunlight. Let this determination guide your choices for plants, since this is the primary indicator of the success of the window box.
Measure the length of the window box to determine the number of plants that will fit in the container. This measurement should include length and width. Window box design involves close placement of annual plants to make the container garden look mature and full at initial planting. Annuals can tolerate crowded conditions as long as the garden receives plenty of water and fertilizer.
Consult the USDA hardiness zone map to determine your local zone. Take this information to the nursery and inspect the annual plants that grow well in your zone for light requirements. Then make decisions based on the color scheme of the exterior of the home. Choose annual plant colors that complement brick or siding or reflect the colors of flowers in other parts of the yard for cohesion. Limit your choices to two to three types of plants to keep the design simple.
Jot down your preferred plants and note pertinent information such as sunlight requirements, watering needs and planting instructions. Plants with similar needs should be grouped together in the window box to ensure success of the container.
Look for plants that use vertical space to make a visually dramatic presence in the container. Trailing vines of blooming petunias and plants with tall spikes use the exterior portions of the planter and the vertical space above it, respectively. Window boxes serve as a focal point in the landscape, and as a result, their design should be dramatic. Avoid excessively tall plants since this will draw attention from other flowers in the container garden.
Determine the correct number of plants for the box. Each annual requires about 4 to 6 inches in the window box. Use the ruler to measure how many plants will fit in the box. Place taller plants at the back of the container, and limit trailing plants to the front and sides unless you're filling the entire window box with vinelike plants.