How to Build Concrete Covered Garden Boxes

Build a garden box that will last into your old age.

A covered garden box provides a protected place for plants to grow. Building the box out of concrete adds another level of protection and creates a container that will last for decades. Select two cardboard boxes to serve as the molds for the planter. One should be smaller than the other -- able to fit inside of the larger box with 3 inches of empty space on all sides. This project requires a few days because of the concrete's drying time.

Things You'll Need

• 2 cardboard boxes
• Pencil
• Utility knife
• Petroleum jelly
• Brush
• Ready-mix concrete
• Water
• Trowel
• Sand
• 1-inch diameter PVC pipes 4 feet long
• Level
• Additional PVC pipe
• PVC elbow joints
• PVC glue
• Soil
• Clear plastic tarp
• Small clamps

Instructions

1. Draw a line around the larger cardboard box that is 6 inches higher than the desired height of the garden box.

2. Cut away unneeded cardboard with a utility knife to make the remaining box more accessible while you work.

3. Brush a layer of petroleum jelly on the interior of the box to allow the cured concrete to slip out of the mold. Place the box on level surface.

4. Fill the bottom 2 inches of the box with ready-mix concrete, mixed with water following the instructions.

5. Smooth the surface of the concrete with a trowel, and allow the concrete to harden overnight.

6. Place the smaller box in the center of the concrete slab.

7. Fill the smaller box with sand to weigh it down, and brush the outer surface with petroleum jelly.

8. Mix more concrete and fill the gap between the two boxes to the desired height, creating the planter's walls. Smooth the surface of the concrete as needed.

9. Allow the concrete to thicken to the consistency of thick peanut butter.

10. Insert 4-foot long, 1-inch diameter PVC pipes into the thickened concrete every 16 inches along both long sides of the planter, set 2 inches in from the edges. Arrange these pipes in pairs with one on either side of the planter, forming ribs to eventually hold the planter's cover. Use a level to ensure they are perfectly vertical.

11. Allow the concrete to harden for another day.

12. Dig out the sand and remove the cardboard from the inside and outside of the garden box. Leave the cardboard under the box; it will eventually decompose.

13. Cut pieces of PVC pipe long enough to join the pairs lining the planter.

14. Connect the pipes to the vertical pairs with elbow joints, applying a bead of PVC glue into the joints before connecting the pipes.

15. Fill the garden box with soil, and drape a clear plastic tarp over the PVC structures. Clamp the tarp in place. It will allow light through but will keep out insects and minor pests.

Tips & Warnings

• Water as needed to keep the soil moist, but not excessively. Although concrete is porous and can absorb some water, over-saturating the garden box could drown the plants.