How to Build a DIY Deck Planter Box

A simple wooden planter box dresses up a bare deck or patio corner and gives you room for herbs, flowers or salad greens without digging a garden bed. This design uses basic butt joints, corner posts and screws, so it’s a good first woodworking project. The details that decide whether it lasts one season or many are the wood, the drainage and keeping the box off the deck surface.

Quick answer: Build the box from cedar or redwood 1x6 boards screwed to 2x2 corner posts, with a slatted or drilled bottom for drainage. Line the sides with landscape fabric, raise the box on small feet, and fill it with potting mix rather than garden soil or a gravel layer. Use exterior-rated screws, and avoid plastic sheeting that traps water against the wood.

Project Overview

Detail	Estimate
Finished size	About 24 in long × 11 in wide × 11 in tall (outside)
Difficulty	Beginner
Build time	2–3 hours
Soil needed	About 1 cubic foot of potting mix
Main costs	Cedar boards, exterior screws, potting mix

Choosing the Wood

Wood	Rot resistance	Notes
Cedar or redwood	Good, naturally	The go-to for planters; no finish required
Pressure-treated lumber	Very good	Modern treatments are widely used, but many gardeners prefer to avoid them for edibles or line them
Untreated pine or fir	Poor	Often breaks down within a few seasons of constant moisture
Composite boards	Excellent	Heavier, pricier, harder to cut cleanly

This build uses cedar. Its natural oils resist rot and insects without chemical treatment.

What You’ll Need

Materials

• Cedar 1x6 boards (actual size about ¾ × 5½ in), about 12 linear feet
• Cedar 2x2 (actual about 1½ × 1½ in), about 4 linear feet
• 1¼ in and 2 in exterior-rated screws (coated or stainless)
• Exterior wood glue (optional)
• Landscape fabric and a staple gun
• Potting mix

Tools

• Drill/driver with countersink bit
• Miter saw or circular saw
• Tape measure, speed square, clamps
• Sandpaper or sanding block

Cut List

Part	Quantity	Length	Notes
Front and back boards	4	24 in	Two boards stacked per side = 11 in tall
End boards	4	9½ in	Fit between the front and back boards
Corner posts (2x2)	4	10½ in	Slightly shorter than the sides so they don’t show on top
Bottom slats	4	About 22½ in	Measure inside and cut to fit; notch the outer slats around the corner posts; leave ¼ in gaps
Bottom cleats (2x2 or 1x2)	2	8 in	Support the bottom slats
Feet	4	1½ in blocks	Keep the box off the deck

The method scales up or down easily. Keep the corner posts slightly shorter than the side height, and recalculate the ends and bottom to match.

Step 1: Build the Ends

Lay two corner posts on a flat surface and screw two end boards across them, flush with the post edges and the top of the boards. Pre-drill every hole; cedar splits easily near board ends. A thin line of exterior glue adds strength. Build the second end the same way.

Step 2: Add the Front and Back

Stand the ends up and attach the long boards, screwing into the corner posts. Check the box for square by measuring the diagonals; they should match.

Step 3: Install the Bottom

Screw the cleats along the inside of the end walls, near the bottom. Lay the bottom slats across the cleats with about ¼ inch between each, which lets water drain freely. If you prefer a solid plywood bottom, drill six to eight ½-inch drainage holes before installing it.

Step 4: Add Feet

Screw small blocks under each corner. Raising the box even an inch lets air circulate under it, so both the planter bottom and your deck boards dry out after rain instead of staying damp and staining.

Step 5: Line and Fill

Staple landscape fabric to the inside walls and across the bottom. The fabric keeps soil in while letting water drain and slows how quickly moisture reaches the wood. Don’t use plastic sheeting across the bottom; it blocks drainage.

Fill with a quality potting mix, not garden soil, which compacts in containers. Skip the old advice to add a layer of gravel or pottery shards: it doesn’t improve drainage and actually leaves a zone of soggy soil above it. Leave about an inch between the soil and the top edge so water doesn’t spill over.

What to Plant

Spot	Good choices
Full sun (6+ hours)	Herbs like basil, thyme and rosemary; peppers; compact tomatoes; marigolds
Part sun (3–6 hours)	Lettuce, spinach, parsley, mint (alone, it spreads), impatiens
Shade	Ferns, hostas, coleus, begonias

Mounting on a Railing

For a railing planter, build the box narrower and attach two cleats or brackets to the back that hook over the railing. Measure your actual railing width, since it varies between decks. A full planter with wet soil is heavy, so keep railing boxes small, use sturdy metal brackets rated for the weight, and check that the railing itself is solid. Test the fit before filling with soil.

Finishing and Weatherproofing

Cedar can be left bare to weather to silver-gray. To keep its color longer, apply an exterior oil or stain to the outside only. Reapply every year or two. Leave the inside unfinished.

Seasonal Care

• Water often. Planters dry out much faster than garden beds, sometimes daily in summer heat. Check with your finger.
• Feed regularly with a liquid or slow-release fertilizer, since potting mix nutrients run out over a season.
• Refresh the soil each spring by replacing the top third with fresh mix and compost.
• Winter: in freezing climates, empty or cover the planter, or store it in a garage, so trapped water doesn’t freeze and stress the joints. Our guide to winterizing outdoor furniture covers other deck items.

Troubleshooting

Problem	Likely cause	Fix
Soil stays soggy	Blocked drainage, gravel layer or dense soil	Clear gaps or holes; replace with potting mix
Boards splitting	Screws too close to ends, no pre-drilling	Pre-drill; use a countersink bit
Rust streaks	Interior screws	Replace with coated or stainless exterior screws
Dark stain on the deck under the box	Box sitting flat on boards	Add feet or furring strips
Box bowing outward	Long sides without support	Add a cross brace inside at mid-length

FAQ

Do I need to line a cedar planter?

It isn’t required, but landscape fabric keeps soil from washing through gaps and slightly extends the wood’s life. Avoid plastic, which traps water.

Can I grow vegetables in a small planter box?

Yes. Herbs, salad greens and compact varieties do well. Larger crops need deeper boxes and more frequent watering.

How long will a cedar planter last?

With good drainage, feet under the box and no plastic liner, a cedar planter can last many years, though exact lifespan depends on climate.

What size screws should I use?

Use 1¼-in exterior screws for board-to-post joints with ¾-in boards, and longer screws where you join thicker parts. Always choose screws rated for exterior use.