Large planter boxes work well for planting herb gardens, big flowers, shrubs and even trees, but also the burden of the plants and potting soil can create it too tough to move planters when needed. Should you include heavy-duty swivel caster wheels on the base of your big planter box, then it is easy to roll the planter across your deck or patio if you want to rearrange your design or only want to sweep around the planter. Choose naturally insect and rot resistant redwood or cedar timber for the planter box material.
Lay six 2-by-6-inch, 24-inch long planks side by side on a flat work surface with the good side of the planks facing out. Set the boards together as tightly as possible.
Measure the six planks to find the true width; while six 2-by-6-inch planks must measure 36 inches, the true width after the boards dry and shrink could be as few as 33 inches.
Cut two pieces of 1-by-4-inch timber with a 45-degree angle miter cut to match the width measurement. The inside of the angle must match the width measurement with the outside of the angle about 1 inch more so the planter fits with corners at a photo frame.
Line up one 1-by-4-inch board horizontally with the top edge and one with the bottom edge of the 2-by-6-inch boards. Drive 2-inch wood screws through the 1-by-4-inch planks and into the 2-by-6-inch planks, using two screws for each 2-by-6-inch board. Repeat this procedure to make an identical second side to your planter box.
Lay three 2-by-6-inch planks side by side on a flat work surface. Measure the true width and then cut two pieces of 1-by-4-inch lumber to match the width, like a 45-degree angle miter cut at each end. Expand the 1-by-4-inch planks to the 2-by-6-inch planks with 2-inch timber screws. Repeat with the remaining three 2-by-6-inch planks to complete the fourth aspect of the planter box.
Hold one short side and one long side together to form an L-shape with the mitered borders of the 1-by-4-inch planks lined up together. Drive 2-inch wood screws through the corners, spaced every four inches along the height of the planks.
Bend the corners of the remaining two pieces together to complete the box and then push 2-inch screws during the corners to secure the sides.
Flip the box upside down and measure the bottom. Cut a bit of half-inch plywood on this dimension and place it over the base of the box. Drive 2-inch wood screws through the plywood, spaced 4 inches apart, to attach the planter box underside.
Measure the inside height of the planter box and then cut four pieces of 1-by-4-inch or 2-by-4-inch lumber for this height. Stand these upright in each corner of the box and then push 2 or 3-inch wood screws through the board and to the planter box. Use 2-inch wood screws should you utilize 1-by-4-inch planks; utilize 3-inch wood screws for 2-by-3-inch corner boards. This isn’t required, but helps to provide increased stability for the planter box corners.
Flip the box over with the underside facing up. Install one heavy duty, plate-mount swivel caster wheel at each corner and one at the middle of each long side, making a total of six swivel caster wheels. As an alternative, you may use one wheel in each corner plus a fifth at the middle of the box. Drive screws through the screw mounting holes in the mounting plates; the screws are usually contained as mounting hardware when you purchase the swivel casters.
Line the inside of the planter with black plastic to protect the timber prior to inserting soil and plants. Add 1 to 2 inches of gravel to the bottom of the planter box. You may also drill drainage holes at the base of the planter box, however this means any excess water will drain on the ground or patio.