How to Build Cedar Planter Boxes | Step-by-Step Plans

Building a cedar planter box requires cutting cedar fence pickets to length, attaching them to corner posts with outdoor screws, adding a slatted bottom for drainage, and applying a weatherproof exterior finish before planting.

A strong wood planter doesn’t need a workshop full of tools or expensive lumber. Cedar fence pickets — typically $2–$4 each at Home Depot and Lowe’s — build a box that holds up to rain, snow, and sun for years without chemical treatment. The method below covers a medium square planter (roughly 20″ × 21″ × 13″) that gives roots about 6 inches of soil depth, ideal for flowers, herbs, and shallow vegetables.

What You Need for a Cedar Planter Box

The short materials list keeps the project simple and under $100. , four 2×2 or 4×4 posts cut to match the box height (roughly 15″–21.5″ depending on your design), and exterior-grade deck screws. A drill, circular saw or hand saw, and sandpaper (60–80 grit followed by 180–220 grit) complete the tool kit. A Kreg pocket hole jig ($50–$100) makes joinery cleaner but is optional.

, so build it at its final location whenever possible. Browse tested cedar planter boxes for ready-built alternatives if you’d rather buy than build.

Planter depth matters: vegetables and most flowers need at least 9–12 inches of soil.

Building the Frame and Sides

Start by trimming about 1/2″ off each end of the pickets for clean, square edges. Sand everything starting with 60–80 grit to knock down rough saw marks, then finish with 180–220 grit for a smooth surface.

Pre-drill holes about 3/4″ from the ends of each picket to prevent splitting — skipping this step is the most common beginner mistake.

Stand those side panels upright and attach the remaining boards to form the third and fourth sides. Check that the box is square — measure corner-to-corner diagonally; both measurements should match.

Installing the Bottom and Drainage

Knot-free cedar naturally resists rot, but standing water will still break down any wood over time.

Finishing and Protecting the Wood

Cedar weathers to a natural silver-gray if left unfinished, but UV exposure and rain will eventually check and crack the surface. Home Depot’s guide on DIY planter boxes recommends exterior finishes rated for ground contact.