What wood is safe for a planter box you grow food in?

Cedar and redwood are the top choices because they resist rot naturally without chemicals, making them safe for edibles and long-lasting. Pressure-treated lumber is fine for ornamental planters, but for food crops many gardeners avoid direct soil contact with treated wood and line the box with plastic as a barrier, since modern treatments are far less toxic than old ones but caution is common. Untreated pine is cheapest but rots within a few seasons. For a deck planter you will grow herbs or vegetables in, cedar lined with plastic is the reliable, safe combination.

How deep does a deck planter box need to be?

Match depth to what you will grow: 6 to 8 inches suits herbs, lettuce, and shallow-rooted flowers; 10 to 12 inches handles most vegetables and perennials; 18 inches or more is better for tomatoes, deep-rooted crops, or small shrubs. Deeper boxes also dry out more slowly, which matters on a hot, breezy deck. Do not go shallower than about 6 inches for anything you want to thrive, since shallow soil dries fast and cramps roots. Size the depth to the plant, then build the box to suit.

How do I keep a planter box from damaging my deck?

Trapped moisture between the planter and the deck boards is what stains and rots decking, so lift the box off the surface and let water escape. Add feet, casters, or cleats so air circulates underneath and the box does not sit flat in a puddle, and make sure drainage holes and any liner direct water away rather than pooling under the box. A drip tray that you actually empty, or simply raising the planter on feet over a spot where water can run off the deck edge, protects the boards beneath.

Do planter boxes need drainage holes and a liner?

Yes to drainage, and usually yes to a liner. Drill several holes in the bottom so excess water escapes, because a box with no drainage drowns roots and rots the wood from the inside. A plastic liner (landscape fabric or perforated plastic sheeting) on the inside walls slows the wood's contact with wet soil, extending the box's life, but the liner must still allow water to drain out the bottom holes, not seal water in. For edibles in treated wood, the liner also acts as a barrier between soil and the lumber.

How long does it take to build a deck planter box?

A simple cedar planter takes an afternoon, about 2 to 4 hours including cutting, assembly, drilling drainage, and lining, at a cost of roughly $40 to $90 depending on size and wood. The build is beginner-friendly: straight cuts and screwed butt joints, no complex joinery required. Most of the time is cutting the pieces and lining the interior. A taller planter with a false bottom (to save soil and weight) or decorative trim adds an hour, but the basic box is one of the easiest outdoor woodworking projects.

How to Build a Deck Planter Box (DIY, Step by Step)

Written & researched by Derek Holt Home & Appliances Editor

Updated August 2026

Over-the-shoulder view of a person grilling vegetables, in soft early-morning light

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Building a deck planter box is a beginner woodworking project you can finish in an afternoon for $40 to $90. It needs a saw, a drill, and rot-resistant lumber — no special skills or joinery. There is nothing structural or code-related about a freestanding planter, so no permit and no pro. The details that make it last and protect your deck are simple: choose cedar or redwood, drill drainage holes, add a liner, and lift the box off the deck boards on feet so trapped water cannot stain or rot the decking beneath.

Plan the size and depth

Decide what you will grow, which sets the depth: 6 to 8 inches for herbs and lettuce, 10 to 12 inches for most vegetables, 18 inches or more for tomatoes and deep roots. Pick a length and width that fits your deck and that you can still reach across to tend. Sketch a cut list. Cedar or redwood is the go-to for a planter you will grow food in.

Low-angle view of a person grilling vegetables, in warm late-afternoon light

Step-by-step build

Cut the pieces. From cedar boards, cut the four side panels to your length and width, corner posts or cleats to join them, and bottom slats. Cut like pieces together for a square box.
Assemble the sides. Screw the side panels to the corner posts with exterior screws and glue, forming the box walls. Check each corner for square as you go.
Add the bottom. Fit the bottom slats across the base with small gaps between them for drainage, screwing them to a bottom cleat or the corner posts.
Drill drainage holes. Bore several 1/2-inch holes through the bottom (in addition to the slat gaps) so water always has an escape.
Attach feet. Add feet, cleats, or casters to lift the box off the deck so air circulates and water drains away rather than pooling under it.
Line the interior. Staple landscape fabric or perforated plastic to the inside walls (not sealing the bottom holes) to slow the wood's contact with wet soil and extend its life.
Sand and finish. Ease sharp edges, sand the exterior, and apply an exterior sealer or stain to the outside. Leave the interior liner to protect the inside.
Fill and plant. Add a false bottom or filler in a deep box to save soil and weight if desired, then fill with potting mix and plant.

Over-the-shoulder view of a person grilling vegetables, in soft overcast light

Tools and materials

You need a circular or miter saw, a drill/driver with a 1/2-inch bit, a staple gun, a level, sandpaper, exterior wood glue and screws, landscape fabric or plastic liner, and cedar or redwood boards. A planter box softens and greens an outdoor living space — line it up along a privacy screen, pair it with a matching outdoor bench built the same way, and place it on a paver patio or deck near your patio furniture to frame the seating area.

Golden-hour view of a person grilling vegetables

Mistakes that rot the box or the deck

No drainage. A sealed bottom drowns roots and rots the box. Drill holes and gap the slats.
Box flat on the deck. Trapped water stains and rots decking. Lift it on feet for airflow.
Untreated pine. It rots in a season or two. Use cedar or redwood, or line treated wood.
Liner sealing the bottom. A watertight liner drowns plants. Keep the drainage holes clear.

Do you need a pro?

No. A freestanding deck planter is pure DIY with no code, permit, or trade involvement. The only considerations are weight and your deck: a large planter full of wet soil is heavy, so on an older or questionable deck, spread the load or place heavy planters near beams and posts rather than mid-span, and have the deck's condition checked if you are unsure it can carry the added weight. For a normal planter on a sound deck, this is an easy, rewarding afternoon build.

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How to Build a Deck Planter Box