How to Build Garden Planters | A Straightforward Build

Building your own garden planter involves cutting lumber to size, assembling a frame with rot-resistant materials, drilling drainage holes, and lining the interior to protect the wood.

A handmade planter can last for years if you choose the right wood and follow a simple assembly sequence. Cedar and pressure-treated lumber resist moisture well, and a basic 5-foot by 3-foot or 8-foot by 4-foot box gives most vegetables and flowers the room they need. The whole project takes an afternoon with basic tools and a trip to the lumber yard.

What Materials Actually Last in a Garden Planter

Rot resistance is the main quality to look for in planter wood. Cedar naturally handles damp soil without chemical treatments, while pressure-treated pine is a budget-friendly alternative that also resists decay. Avoid untreated framing lumber — it will rot from the inside within a year or two. You will also need exterior-grade wood screws (deck screws work well), landscape fabric or heavy-duty plastic sheeting, and a gravel layer for drainage at the bottom of the box.

If you want to skip the cutting and measuring entirely, pre-built options in our planter roundup arrive ready to fill with soil, which can be faster than a full DIY build.

The Standard Dimensions and Assembly Order

A planter between 12 and 24 inches deep gives most root systems enough space. The most common beginner-friendly sizes are 5 feet by 3 feet or 8 feet by 4 feet, both of which work with standard 8-foot lumber lengths with minimal waste.

Building the Frame

Cut your lumber to the side and end lengths you need, then attach the side panels to corner posts using exterior wood screws. For a 5×3 planter, cut two 5-foot pieces for the long sides and two 3-foot pieces for the short sides. Screw through the side pieces into 4×4 corner posts at each end. Space additional slats or boards evenly along the sides to form the walls, leaving a small gap between each board for airflow.

Adding the Base and Drainage

Attach the floor boards to the bottom of the frame, then drill at least five evenly-spaced drainage holes, each about 3/4-inch wide, through the floor. Holes smaller than that can clog with soil; larger ones let the gravel layer fall through. Line the interior with landscape fabric or plastic sheeting, then cut small slits over each drainage hole so water can escape. Spread a 2-inch layer of gravel across the bottom before adding soil — this keeps the drainage holes clear and prevents the soil from getting waterlogged.

How to Protect the Wood and Extend the Planter’s Life

Sand down any rough edges before assembly to prevent splinters, then apply a water-resistant sealant or wood preservative to all bare surfaces — especially the interior face that will contact damp soil. Let the sealant fully dry before adding the fabric liner or gravel. Reapply sealant once a year on the outside of the planter to keep the wood from cracking or warping over the growing season.

If you are building an in-ground raised bed instead of a freestanding planter, call 811 before you dig to have underground utilities marked. This is a free service in the US and prevents accidentally cutting a gas line or buried cable.

FAQs

Can I use regular pine for a garden planter?

Pressure-treated pine or cedar is a better choice for long-term use with minimal maintenance.

How deep should a planter be for vegetables?

Most vegetables need at least 12 inches of soil depth. Root crops like carrots and potatoes grow best in planters that are 18 to 24 inches deep. Shallow-rooted greens and herbs can manage in 8 to 10 inches.

Do I need to seal the inside of a cedar planter?

Use a plant-safe sealant and let it cure fully before adding the liner.