A little time and less than $20 made this cool window box planter

(TL/DR: Click here to skip straight to the instructions)

Our house is a 1950’s single story California ranch. Long and low, it has lots of big windows that bring in fresh air and light keeping the house cool in the summer and naturally lit in the winter. The guest bathroom has a large window with a view out across the deck down to the orange grove. The glass is frosted to provide privacy, but most of the time it’s wide open and people don’t realize that anyone on the deck has a clear view into the bathroom.

To limit the awkward accidental eye contact, I had a big ficus in a 35 gallon pot on the deck in front of the window as a screen, but several nights of hard freeze killed it this last winter so the window was once again bare.

I didn’t have another big tree to put in place (plus they’re too heavy), so I dorked around with a few ideas until my wife finally said “why don’t you build a window box planter?”

Not a bad idea, I thought. I dug through my surplus building stuff and came up with a couple dog-eared cedar fence boards for the box itself and a piece of corrugated steel sheet I could wrap the box in to give it a sort of rustic livestock “water trough” look.

Raw materials among the surplus building stuff

The whole thing — materials and plants — cost less than $20 and took only a weekend to put together. Not only does it look great and screen the window really well, but it also frees up a bunch of room on the deck for the lounge chairs and side table. Win-win-win.

Here’s how I built the window box. Feel free to copy, modify or improve on it any way you like.

Corrugated Steel & Cedar Window Box Planter

Materials
  • 2 Cedar Fence Pickets 1-in x 8-in x 6-ft
  • 1-in x 2-in x 20-in piece of wood (can be pine, redwood, etc. Any old scrap will do)
  • 1 sheet corrugated steel at least 48-in long
  • Waterproof Wood Glue
  • 1½-in finish nails
  • 5/8-in wood screws
  • 2 galvanized steel corner brackets rated for 30 lbs or more (Mine were 2-in.)
Instructions

The finished size of the window box is 30-in x 9½-in x 9½-in.

Planter box diagram view from the front

The wood planter itself is two inches smaller in all dimensions which lets it hide inside of the steel so the planter looks like it’s a real corrugated steel trough.

Diagram of planter box assembly from the top

Step 1 – Cut the Wood

The cut boards ready for assembly


The wood box is 7½-in tall and wide because the cedar fence pickets are already 7½-in wide, which means you only have to cut them to length as follows:

  • 2 x 28-in (front and back)
  • 1 x 27-in (bottom)
  • 2 x 7½-in (ends)

(Cedar pickets are prone to splitting so make sure to check the boards and cut off any ends with cracks or splits before you cut your longer boards.)

Once the cedar is cut, get your 1×2 and cut two pieces:

  • 2 x 8½-in

These will be the supports that will prevent the cedar bottom from warping or splitting once it’s mounted and has plants in it.

Step 2 – Assemble the Cedar Box

Starting with the box bottom glue and nail the end pieces to the bottom. The end pieces should be mounted to the outside of the bottom, not on top of it. Once again, because cedar can split, be careful when securing the piece with the finish nails.

Beginning with the ends, use waterproof wood glue and finish nails to assemble the box.

Once the ends are on, glue and nail the box sides to finish the box.

Gluing and nailing the cedar box

Flip the box over and attach the supports to the bottom of the box with glue and nails. The supports should be mounted on each side of the bottom halfway between the outer edge and the center of the box.

Mounting bottom supports and drilling drain holes in the box

Finally, using a 3/8-in wood bit, drill a set of six drainage holes in the bottom.

Set the box aside and let the glue dry (about 2 hours should do it).

Step 3 – Cut Corrugated Steel Pieces

A standard sheet of corrugated steel is 26 inches wide, which is too short for the box, so rather than running the corrugation vertically as I had planned, I ran it horizontally. Turns out it worked better because it’s a lot easier to cut the panel with tin snips when you’re cutting along the bottom of the corrugated curve rather than across it. Pieces cut:

  • 2 – 9½-in x 30-in (front & back)
  • 2 – 9½-in x 8½-in (end pieces)

Once they’re cut, use a file to remove sharp pieces and metal burrs from the edges.

Step 4 – Attach Steel Sheets

Once the glue on the box is dry, it’s time to attach the steel panels to the wood.

Use a pencil and straight rule to make a line 1 inch from the long edge of both pieces of steel you cut for the front and back. Align it with the top of your wood box and make sure that the bottom completely hides the support bars on the bottom of the box (a pair of spring clamps makes this a lot easier).

Using clamps and 5/8-inch screws to attach the corrugated panels to the box

Screw the panel to the box with the 5/8-in wood screws. Screw through the panel at the bottom of the corrugated curve to ensure good contact with the wood under it. Mount the other panel to the other side of the box the same way.

Once the front and back panels are attached, put the end panels and put it in place, align them so they’re even with the front and back, and screw them to the box as well.

Corrugated panels mounted on the cedar planter box

Step 5 – Attach Mounting Brackets

Mark where the mounting brackets will go on the back of the window box and use tin snips to clip out a slot wide enough to allow the bracket to slide down between the steel panel and the wood so the mounting holes are level with the top of the wood box (not the steel panel). Attach the brackets to the wood with screws.

Step 6 – Paint

You don’t actually have to paint this window box, because the steel will build up a nice patina over time. However, scratches and cuts to the metal will allow rust, which will ultimately drip and stain whatever is under the window box. In my case, that’s a redwood deck, so I painted.

Painting all the exposed edges of the box with a rust-colored primer

I’m in this brick red phase, so I decided to paint the box with brick red primer. I painted the outside and top (but not the inside or bottom) with a couple of coats of primer, and then added a third coat just because I felt like it.

Step 7 – Mount

Mounting is pretty straightforward. Center the empty window box on the sill where you plan to mount it, and mark the locations of the angle bracket’s screw holes. Drill pilot holes in the sill, set the box and brackets back in place and attach to the window sill with screws (I used 1-⅜-in exterior wood screws).

Step 8 – Fill and Enjoy

The space where the window box hangs doesn’t get much sun and I’m not very good with shade plants, so I left the plant selection to the Mrs. who chose a couple of fuschias, a tall burgundy coleus, and a few little pink and green coleuses to soften the edges.

Planter box filled and mounted in the window

As you can see from this photo one month later, all the plants seem to be doing quite well. Best of all, the risk of awkward accidental eye contact is practically nil.

Planter box at night looks cool even if you can’t see the plants

author avatar
Sage Osterfeld
I’m just a guy with nearly an acre of dirt, a nice little mid-century ranch house and a near-perfect climate. But in my mind I’m a landscaper survivalist craftsman chef naturalist with a barbeque the size of a VW and my own cable TV show. I like to write about the stuff I build, grow and see here at Sage's Acre.