Gather the appropriate scrap wood you want to use. I used torn down privacy fence.

Supplies

One section of wood cut to size. I added +3 inches to both sides. With the planter I used the overall length of the base was 28”

Step 1: Place Long Sides Onto Base

Using clamps affix and adjust the sides you are using.

Then using a fostner bit 1/4” drill holes into both pieces of woods.

Release your clamps and glue your mating surfaces. Insert your dowels and affix the side and clamp.

Repeat that process for the opposite side. Saw off excess dowel and use light percussion to seat the dowels all the way in.

Step 2: Capstone

Cut out find an appropriately sized send piece for both sides and shot them in. Using the same procedure for inserting 1/4” dowels fix sides into place.

Fully clamp the finished product and drill 3 large drain holes in the bottom.

You could sand and stain but the wood I used is from an old fence and is rot resistant.