How To Install A Window Mounted Flower Box

2-3 hours per box
No Room For A Garden? Think Outside the Box!


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Even if your home doesn't feature views of a rolling forest, a meadow, or a tidy flower garden, you can still put color and fragrance right under your nose. One of the fastest (and easiest) ways to bring springtime both inside and out, is to add a few flower boxes to your windows. With the right selection of flowers and plants, you can add a tremendous amount of color and charm in a single weekend.

Decisions, Decisions

When it comes to installing window boxes, there are a number of different choices. Since windows vary greatly in size, it's important to measure the dimensions of your particular window before moving forward. If your windows are a fairly standard size, there are many do-it-yourself kits that are simple to assemble and mount. If you've got more time and are handy with lumber and a saw, you can build your own boxes from scratch or with the help of some freely available plans.

Project Steps

Step 1

Measure it!

Measure each window from side to side to get the proper dimensions of your window box. For older homes, measurements may vary, so don't assume uniformity even if they look the same.

Step 2

Assemble it!


Assemble the pieces according to the directions that came with your specific kit. To help make your window box last as long as possible, seal all joints and cracks with silicone based caulking which will seal the joints and act as an adhesive to strengthen your box.

Tool Tip: You can save time with a cordless power caulking gun, available at most home improvement stores.

Step 3

Drain it!

If there are no drainage holes in the window box you've chosen, be sure to drill 1/2" holes in the bottom of the box, 3" in from each side. The length of the box will determine whether you drill one or two evenly spaced drainage holes in the middle. Remember that without drainage your precious plants will soon suffer from rot and other problems.

Step 4

Paint it!


If you choose to paint your window box, assuming it's wood, you'll want to start by first applying a primer. Since your window box will be exposed to the elements during most of its life, a primer will help the paint adhere better and last longer. Once dry, paint your window box and brackets a color that complements your house. And remember, you can paint your window box however you wish let your imagination run wild!

Step 5

Building It Yourself?

If you can't find a kit that suits your taste or style, you might choose to build it yourself. The obvious advantage is that you can customize the design and size to match the windows of your house. Also, this is a simple project that would be great to test your budding Jane skills!

There are literally hundreds of plans you can download off the Internet--a quick search for "window box plans" returns many that are free of charge. Most of these plans are easy to follow and easy to customize.

If you decide to go this route, use pressure treated lumber over the usual cedar, pine, fiberglass or plastic. It lasts longer, is sturdy enough to hold wet soil, won't crack or split where it attaches to your house, is bug resistant and repels moisture.

Jane Tip: If building it seems like too much work, that doesn't mean you can't customize one of the existing window box kits. Using a jigsaw, you can alter the shape of the window box however you see fit! Just be sure not to cut too much or you might affect the integrity of the box. You can also add molding to the front to give it a bit of added flair.

Step 6

Mount it!

How you attach the box to the house depends on your home's siding. For most types of siding, a 3" galvanized screw and a wooden mounting bracket will work well. Where you attach it depends on your windows. For double hung or sliding glass windows, place the top of the bracket 1" below the sill. For swing-out windows, measure down 6-8 inches to accommodate your plantings. Mark your measurements with a pencil and use the level to make sure your marks are even. Note that one side of the sill may be higher, so when making your marks, keep the planter level to the ground rather than to the window sill.

Safety Tip: Window boxes longer than 48 inches need a third, center bracket when mounting.

Next, hold the first bracket with its top on the pencil mark, and mark the bracket for the top screw hole so it falls near the bottom of the first piece of siding below the window. Use your drill to bore a pilot hole at the second mark, and bore a second hole into the bracket at the corresponding mark. Fasten the bracket to the house with a 3-inch-long galvanized decking screw through the holes you just made. Hold the level against the side of the bracket to ensure that hangs down straight.

Jane Tip: It may seem obvious, but fill your window box after you mount it. Dirt is heavy!

For the bottom of the bracket, bore a pilot hole through the bracket just above the horizontal leg, where it will be hidden by the window box, and bore the corresponding hole into the siding of the house, then drive the second 3-inch screw through the bracket to secure.

Do the same for the remaining bracket(s), holding up your level each time to be sure everything is aligned.

Place the empty window box on the brackets. Center the box on the brackets, measuring the overhang on either end. Drill pilot holes into the upper rear edge of the box down into each bracket, then drive a 2 1/2-inch-long galvanized screw through each pilot hole and tighten as needed.

If at all possible, be sure you attach your brackets into your building's studs (vertical pieces of lumber, typically 2x4, on which the walls are constructed) and not just into the stucco or siding. There are typically three studs (a king, a trimmer, and a cripple) on each side of a window's rough opening, so there is plenty of solid backing to attach to. As an alternative, if your house's exterior has stucco or plywood sheathing, you can use large hollow wall anchors to secure the brackets without having to find a stud. Also, it is a good idea to shoot some caulking into the hole before you screw in the anchors. This will seal the hole and assure that no moisture seeps into the structure itself.

Step 7

Time to Beautify

For planting, we recommend inserting a plastic container with your plants or a few smaller pots rather than filling the window box directly. This will minimize the water damage that occurs over time. Check with your local garden center for seasonally appropriate arrangements.

Jane Tip: Purchase container inserts before building. It saves you the hassle of searching high and low for the perfect fit once your project is complete. If your planter is in a second-story window or above, insert your plants rather than filling the window box directly and create low-maintenance arrangements.

Flowers always add beauty and color, and evergreens never need to be swapped out, but you can also thinking outside the (flower) box. Create an edible arrangement, with herbs, fruits, vegetables or a nice mix. In summer, try a fragrant and tasty mix of basil and miniature tomatoes. Alternately, flowering strawberries add beauty, fragrance and good snacking.

Jane Tip: Mix plenty of peat moss in with the dirt. Peat moss holds moisture so you don't need to water as often and place a filter layer of small stones over the holes in the bottom of your planter to keep the dirt from washing through.

Window boxes are a great way to add color and flair to the exterior of any home. It's also a great way to enhance your view from the inside as you get a burst of color every time you look out the window. And nothing will brighten up the day—everyday—as the scent of fresh flowers, especially if they're right outside your window.

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