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Window Boxes

Window Boxes

window box window box Many houses' styles are brightened and improved with colorful flowers in window boxes. These boxes are simple to build and in a weekend you can dress up your home and add the color and beauty the flowers can bring.

There are a variety of approaches you can use. I will discuss these two in this article.

Planting directly in the box.

I have used this method for many years. The box holds the dirt directly inside it, and therefore should be made of pressure treated wood. I have tried cedar, but it didn't last as long as the pressure treated wood. The soil and peat moss is added to the box and freshened each year and the flowers do just fine. This is a relatively simple approach.

Planting in a planter inside a box.

If you build the box to hold a planter you can make the box out of any wood although I would use pressure treated wood at least for the bottoms and the inside should be painted as well as the outside. The advantage here is you can lift the planter out of the box to pot the plants and change out the soil. I think this method is best for second story windows or any window too high to get to from the ground.

Determining the size

To make your planter, it will have to be custom designed for your windows. And this of course, besides the cost and pleasure of doing it yourself is why you will want to make them in the first place. The box should be as wide as the window and frame including trim. You can vary that of course to your taste but I find this seems to be the most appealing (my own opinion). Measure the width of your window and frame and this is your boxes length.

If you are going to place a long plastic planter in the box rather than plant directly in the box, go to the store and buy your planters now. Their width, depth and even length will determine the size box you will make. You can use the general directions given here, but make your dimensions fit your planters' size at a minimum. If you are planting directly into the box, you can use the dimensions I provide, but recognize they are not critical. Varying them slightly will not alter the final look.

Window Box

Pressure treated wood is hard to come by in all the sizes you need, though it is getting better. My boxes are built, to a degree based on the available lumber size. I have found pressure treated 1x8's, so 7 inches has become my largest dimension. This keeps you from having to joint two boards together.

The box will then be 8 inches wide at the top, 6 inches wide at the bottom and roughly 7 inches deep.

Building the window box

Start by cutting the end boards.

window box ends

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Next cut the front, back and bottom boards. The dimensions for the length should be the one determined by your windows. The width of the front board will be the total width of your board, 7 (assuming you are using 1x8's). The back board is cut square 7 inches wide. The bottom board should be cut 5 inches wide with a 20 degree angle to make it meet the front board squarely on the front. (5 inches will be the short dimension).

bottom of the window box To assemble your box, use galvanized exterior wood screws and galvanized 6d finishing nails. The screws should be 1 long. I always countersink the screws and cover them with elmer's wood filler. Drill inch holes, about an 1/8 in deep, 2 for each the front, bottom and back. Then drill the hole all the way through the end boards with a bit about the size of your screws threads.

screw holes in end of windowbox Now screw the end boards on to the front, back and bottom. The exterior screws shouldn't need a pilot hole in the front, back and bottom boards, however if they are hard going in, put a little soap on the threads to make them go in easier.

Next nail along the front and back at the bottom into the bottom board fastening it to the front and back boards. Countersink all the nails and then cover all nail holes and screws with the wood putty.

Drill a inch hole every 6 inches into the bottom board along the center of the board to allow water to drain out.

Finally, prime and then paint the boxes an accent color to compliment your house's colors.


Mounting the boxes always seems to present a problem. I hate putting holes in a house. I have found that mounting them from the window's sill works well. But I have also seen them screwed directly into the side of the house where the siding was wood. In any case I will describe the method I have used to hang them from the sill. Buy 3 inch T brackets. Two for each box. These should be painted to match the window sill.

Evenly spaced from either side, bolt them to the window box. Use galvanized or stainless steel bolts/nuts etc. The horizontal top part of the T should be just above the back of the window box. Using stainless steel screws, screw the top of the T into the window sill.


For planting it is best to have plenty of peat moss mixed in with the dirt to hold the moisture so you don't need to water as often. I always place a small stone over the holes to keep the dirt from washing through.

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