My wife wants me to install a window box or flower box, depending on what you call them. I’m pretty sure that if I’m successful, I’ll be installing a few more. The boxes, when full of potting soil, plants and water, are pretty heavy. I’m concerned that the box is going to crash to the ground. What works best when installing these decorative items? — Don B., Staten Island, N.Y.

Your foremost concern needs to be the safety of anyone who might walk under the window. You sure don’t want a flower box to detach from a wall and fall on someone’s head. It has happened and surely will happen again.

There are several ways to support a flower box, the most common being metal brackets screwed to the wall. The challenge when using a bracket is to make sure the screws go into solid lumber. The only problem with this approach is that the placement of the brackets might not be centered under the flower box. Centering brackets on a masonry wall is easy, and it’s easy to anchor them for solid support.

This is why I usually don’t use brackets but hidden French cleats. They are a time-tested method to secure pictures, mirrors, mantles and even window boxes to a wall.

The French cleat is a two-piece connection system in which the piece of wood or metal that’s attached to the window box interlocks with the mating piece attached to the wall. The best part is that once it is installed, the window box will appear to be floating in midair with no visible means of support.

It’s easiest to use lumber to create a French cleat. I recommend using treated lumber in your case, since the wood will be subjected to water. You don’t want the French cleat to rot over time and fail, causing the window box to crash to the ground.

The French cleat can be made from 3 / 4-inch thick material. You need a piece of lumber that’s about three inches wide and as long as the window box. The magic happens when you cut the single piece of lumber into two pieces along its length. You need a circular handsaw or, better yet, a table saw with the blade set at a 45-degree angle.

By splitting the piece of wood down the middle with the saw set at that angle, you create two pieces of lumber that look identical, but one actually interlocks with the other when mated. This is what’s going to hold the window box to the wall.

The piece of lumber that attaches to the window box is screwed to the window box so that the angled cut points to the ground and the long tip of the cut is not touching the back of the window box. The flat or square edge of this piece is usually flush with the top of the rear of the window box.

The other piece of lumber gets screwed to the wall of the house with the angled cut pointing up to the sky and the long point not touching the wall.

When you bring the window box over to the wall and allow the two pieces of lumber to interlock, the box will be securely attached to the wall. The only tricky measuring you have to do is to calculate how far below the bottom of the windowsill or window frame to attach the piece to the house.

Typically, the top of the window box, once installed, is a inch or so below the window sill or the outer frame of the window. It’s easy to do the math to see where the bottom of the house piece needs to be for the box to be at the right height. If you started with a piece of lumber three inches wide, the square bottom of the house piece needs to be four inches below the bottom of the windowsill or window frame.

—Tribune Media

Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site, askthebuilder.