How to Make a Large Concrete Planter | Build Your Own for a Fraction of the Cost

A large concrete planter is built by constructing two nested plywood molds, pouring a 2-inch base, and filling the cavity with concrete mixed to a peanut butter consistency for a smooth, durable finish.

Finding a massive concrete planter at a garden center that doesn’t cost a small fortune is nearly impossible. One DIYer saved roughly $1,200 by building a 24-inch by 32-inch planter at home instead of buying one. The process is straightforward for any weekend warrior: you build two plywood boxes, pour concrete between them, and wait for it to cure. The result is a heavy, custom-sized planter that will last for decades on your patio or in your garden. Here is the exact method that works, with the mistakes to avoid so you only do this once.

Materials and Dimensions Needed for a Large Concrete Planter

The planter in this guide finishes at roughly 24 inches wide by 24 inches deep by 32 inches tall, with 2-inch-thick walls. You will adjust these dimensions as needed, but the building method stays the same.

For the concrete mix, use standard bagged concrete mix (not plain cement mix – concrete includes the aggregate needed for strength). Mix it to a “peanut butter” consistency: moist enough to hold its shape when squeezed but not slushy or watery. For a very large planter like this one, plan on roughly 10 bags of 50-pound concrete, though your total depends on the exact dimensions.

How to Make a Large Concrete Planter: Step-by-Step

Start by cutting all plywood panels to the sizes listed in the table above. Assemble the outer box by screwing the four 24″ × 32″ side panels to the 24″ × 24″ bottom panel. Build the inner mold the same way using the smaller side panels and its 22″ × 22″ bottom.

Step 1: Install the Drainage System

Drill a 2-inch diameter hole through the center of the outer mold’s bottom panel. Push one end of the PVC pipe through the hole so that the pipe extends about 2 inches up from the bottom inside the mold. This creates the drainage void. Cover the top of that pipe with tape or a plastic cap to keep concrete out of it during the pour.

Step 2: Pour the Base Layer

Mix your concrete to the peanut butter consistency described above. Pour a 2-inch layer of concrete into the bottom of the outer mold, covering the entire base area. Spread it evenly and tap the sides of the outer mold with a rubber mallet to settle the mix and release any air bubbles.

Step 3: Position the Inner Mold

Lower the inner mold into the outer mold and rest it directly on top of the fresh 2-inch base layer. Center it so there is an even gap on all four sides. Screw the 2-inch spacing blocks to the top edges of the inner and outer molds to lock that position. The blocks guarantee a uniform 2-inch wall thickness all the way around.

Step 4: Fill the Cavity

Now fill the 2-inch gap between the two molds with your concrete mix. Work in layers—fill about 6 inches at a time, then tap the outer mold with the rubber mallet on all sides to consolidate the concrete. Continue until the mix reaches the top of the mold. The top surface can be smoothed with a trowel or left with a slight texture for a more natural look.

Step 5: Cure the Concrete

Let the planter sit undisturbed for a minimum of 24 hours. For thicker sections and stronger results, leave it in the mold for several days. Keep the mold out of direct sunlight during the cure. After removing the molds, you can submerge the entire planter in water for one week to achieve full hydration and maximum strength.

Step 6: Remove the Molds and Finish

Unscrew and remove the outer mold panels. If the inner mold is stuck, gently pry it apart using a flat screwdriver and mallet. Wear a dust mask or respirator, and sand outdoors on a breezy day to avoid inhaling concrete dust. Use a sanding stone or block to smooth any rough edges. Rinse the planter clean with water. Once it is dry, apply a concrete cure-and-seal product. If the planter will sit uncovered outdoors, use a matte sealant to protect it from weather and water damage.

If you want to see photos of finished examples and compare sizes before deciding on your own project, check out our roundup of the best large concrete planters for inspiration and size reference.

Common Mistakes to Avoid When Making a Concrete Planter

Every error below is fixable—but avoiding them entirely saves hours of frustration and a ruined pour.

• Overwatering the mix. Concrete that is too wet leads to cracking during drying. Stick to the peanut butter consistency.
• Skipping mold lubrication. A plastic or cardboard mold that isn’t coated with petroleum jelly or cooking spray will grab the concrete. Cardboard can be ripped away dry, but plastic needs lubrication.
• No drainage hole. A planter without drainage drowns your plants. The PVC pipe method works perfectly.
• Inconsistent spacing. Without the 2-inch spacing blocks screwed to the edges, the inner mold shifts and leaves uneven walls.
• Removing the mold too early. Before 24 hours the concrete is structurally weak. Patience here is the difference between a planter and a pile of rubble.
• Not tapping the box. Air bubbles and voids hide in the mix. The rubber mallet is your best friend during every pour layer.
• Sanding indoors. Concrete dust is hazardous. Always sand outside in a breeze.

What to Do If the Planter Cracks or Has Air Pockets

Small surface cracks or shallow air pockets are cosmetic, not structural. Fill them with a concrete patching compound, let it dry, and sand flush. Deep structural cracks mean a failed pour—scrap that planter and start again. The most common cause is overwatering the mix or removing the mold too early. If the walls feel weak or crumbly, the concrete-to-water ratio was off, and the planter won’t hold up outdoors.

Mold Alternatives When You Don’t Want to Build Plywood Boxes

You don’t have to build 32-inch-tall plywood molds for every project. For smaller planters, recycled plastic containers like sour cream tubs or salsa containers work well. Coat the inside with petroleum jelly before pouring. Cardboard boxes, taped together, also work—you just rip the cardboard away dry after the concrete cures. A standard straw or chopstick poked through both containers creates drainage. These methods are faster and cheaper for small pots, but they won’t produce the clean, straight lines of the plywood box method.

Final Checklist for a Successful Large Concrete Planter Pour

Before you pour, confirm each of these points. It turns a messy project into a controlled one.

• All plywood panels are cut and assembled before mixing concrete.
• Drainage PVC is installed and capped.
• Inner and outer molds are centered with spacing blocks locked in place.
• Concrete is mixed to peanut butter consistency—no slumps, no crumbles.
• Rubber mallet is ready for tapping.
• Planter will sit out of direct sunlight for 24 hours minimum.
• Safety glasses and dust mask are set out for the sanding phase.
• Concrete cure-and-seal is purchased and ready for the finish coat.