How to Build a DIY Railing Planter

Planning and Building the Railing Planter's Box

To plan and build the planter box for your railing planter, follow the instructions below. These steps are meant to be adjustable in order to allow you to customize the size and nature of the box to best suit your needs.

1. Determine the Dimensions
   

   Before you head to the hardware store, first determine your planter's dimensions, along with how many planters you want to build. To figure your dimensions for the planter, you first need to decide whether or not you want to use a planter box insert or not. A coco fiber insert will help the planter retain moisture. You also will need to factor in the size and spacing that will best suit your railing.

   Once you determine your dimensions, use these numbers to gather your materials. We recommend using cedar wood, as it has great resistance to the elements.
   

2. Measure and Cut Your Lumber

   Using a miter saw, cut your boards to length. Because the long sides will be placed overtop of the short sides, their length will be the full length of the planter. Likewise, the length of the short sides will determine the interior depth of the planter. A fifth board should be cut to fit inside the bottom, flush on all sides. If necessary, use a table saw to rip the board to a custom width.
   

   Tip

   If you don't own a table saw for ripping, it's a good idea to alter the short side lengths to account for an unaltered board to fit in the bottom.

3. Sand the Boards

   To improve the bond of the glue and remove any splinters, thoroughly sand the entirety of each board using an orbital sander and 120-grit sandpaper. Once smooth, remove all dust with a tack cloth.
   

4. Mock up the Box

   Whenever you're working with glue, it's best to familiarize yourself with the assembly process before applying the glue. This way, you can work quickly and efficiently once the glue is on the wood. Since the priority will be the front of the box, place the long sides over top of the short sides to hide the end grain.
   

5. Assemble the Planter Box Sides

   Assembling the planter is as easy as gluing the joints and nailing the boards together. We recommend a 16-gauge nail gun for its speed and ease, but a simple hammer and brad nails will also do the trick. The nails themselves are merely there to tightly hold the boards together as the glue dries, as the glue itself is stronger than the hold of the nails.

   Warning

   While a brad nailer is handy and can save you a lot of time, special attention should be paid whenever using this tool and other power tools. Brad nails can wander when you drive them, causing them to quickly exit out the side of the material you are nailing. For this reason, always wear safety glasses, and keep your support hand out of harm's way.

   Apply glue to each side of the joints, and press the boards together. Once perfectly aligned, drive nails every two inches and at each end. Promptly wipe any excess glue using a rag.
   

6. Secure the Bottom Piece

   To add the bottom piece, apply a thin layer of glue along the entire edge of the bottom piece and the corresponding spot on the inside of the box. Slide the bottom into the box, lightly tapping with a rubber mallet if it won't easily slide into place. Once properly aligned, carefully drive nails around the perimeter, approximately every two inches.
   

7. Drill Drain Holes

   To prevent water from collecting inside the planter, drill three to four drain holes in the bottom using a 1/2-inch drill bit.
   

8. Seal the Wood

   While cedar has excellent weather resistance, it will become gray over time. For some people, this is fine, as they appreciate its weathered appearance. However, if you wish for cedar to stay good as new for years to come, apply a clear sealant with UV protection according to the manufacturer's instructions.
   

9. Add Corner Braces

   Plants are heavy, so it's a good idea to add some bracing to your planter box before adding plants. For this, simply install small L-brackets with 5/8-inch wood screws spanning each of the corners. For most planters, two in each corner is adequate, but this number can be adjusted depending on the size of your planter. Furthermore, it's your choice whether you'd like to place the brackets on the inside to maintain the planter's sleek look, or on the outside to add a more industrial accent.
   

Ways to Hang Your DIY Planter

How to Hang With Railing Hooks

The main way of mounting planter boxes to your railing is to attach railing brackets to the box. These metal brackets screw directly into the back of the planter and drape over the top of the railing, supporting the weight of the planter. This is a great option for those with non-wood railings, as it doesn't require screwing into the railing itself.

How to Hang With a French Cleat

A French cleat is a fancy term for a piece of wood cut down the middle at a 45-degree angle. One side of the board is attached to a wall or fixed object and the other is attached to the object that is to be mounted. Once the angles are joined together once more, the angles seat and hold the item in place. This is a great option for wooden railings, as it provides a solid mounting point that is easily removed and hidden from view.

1. Create French Cleat

   Cut an exterior-grade scrap piece of wood to a length just shy of the length of your planter. The wood piece must be have a wide and short dimension (1-inch by 4-inches, for example). Set your table saw blade to 45 degrees and, with the wider dimension laying flat, rip the board down the middle.
   

2. Attach French Cleat

   Using self-drilling wood screws long enough to penetrate both the cleat and the wood it is resting against, fasten one side of the cleat to the back of the planter so that the angle creates a downward-facing pocket. Attach the other side of the cleat to the railing to create an upward-facing pocket.
   

3. Mount the Planter

   Mount the planter to the railing by seating the two angles together.