Best Cedar Planter Boxes for Decks and Gardens

The best cedar planter boxes for most decks and gardens are 36 to 48-inch long Western Red Cedar boxes made from clear or tight-knot heartwood, with 10 to 12-inch depth, end-wall drainage holes positioned 1/2 to 3/4 inch above the base, and an optional fabric liner for soil retention rather than rot prevention.

That combination balances root space for vegetables and ornamentals, resists rot for 8-12 years outdoors without chemical treatment, and drains correctly whether the box sits on deck boards, concrete, or soil. Shorter or shallower boxes work for herbs and annuals but dry out too fast and heave in winter, while untreated sapwood cedar boxes can soften in 3-5 seasons even with a liner.

How to Choose: The 4 Decision Criteria That Matter

1. Dimensions vs. What You Want to Grow

Size determines both plant health and weight on a deck. A common mistake is buying a narrow 7-inch wide window-box style planter for tomatoes or carrots, which need lateral and vertical root room.

• Herbs and lettuce: 24″ L x 12″ W x 8″ D is sufficient. Holds about 1 cubic foot (7.5 gallons) of soil mix per 24-inch section.
• Peppers, bush beans, strawberries: 36″ L x 14″ W x 10″ D minimum. Holds 2.2-2.6 cubic feet. This is the sweet spot for deck rail or bench-height boxes.
• Tomatoes, cucumbers, dwarf citrus: 48″ L x 18″ W x 12-14″ D or a square 24″ x 24″ x 16″ deep box. Holds 4.5-6 cubic feet and supports deeper roots and staking.
• Weight when watered: Soil mix weighs 40-50 lbs per cubic foot when saturated. A 48″ x 14″ x 12″ box with 4.5 cu ft of mix weighs 180-225 lbs before plants and water reservoir. Confirm deck load capacity and use feet or risers to spread weight and allow airflow.

2. Cedar Grade and Rot Resistance

Not all cedar is equal. Durability comes from heartwood content, not just the species name.

• Western Red Cedar – Clear Heartwood: Highest natural resistance. Uniform reddish-brown color, no knots. Typically lasts 10-15 years outdoors unfinished, 12+ if elevated off the ground. Most expensive.
• Western Red Cedar – Tight-Knot or Select Knotty: Heartwood with small, tight knots. Very good resistance (8-12 years) and better value. This is what most premium planter brands like CedarCraft and Real Wood Products use. Avoid if knots are large, loose, or falling out.
• Western Red Cedar – Sapwood: Pale yellow-white streaks. Sapwood has little rot resistance and will soften, turn spongy, and attract fungi in 2-4 years in contact with wet soil, liner or not. Inspect boards – if more than 15-20% of the surface is sapwood, service life drops sharply.
• White Cedar (Northern/ Eastern): Lighter, slightly less rot-resistant than Western Red but still good for 6-10 years. Often sold as more affordable kits.
• Chinese Fir / Cedar-toned softwoods: Marketed as cedar alternatives. Much lower durability (3-5 years) without a thick liner and regular sealing. Not true cedar for multi-season use.

Thickness also matters. 5/8-inch boards are standard for 24-36 inch boxes, but 3/4 to 7/8-inch boards resist warping and bowing when soil is wet for boxes over 42 inches long. Look for corner joinery with stainless steel or coated deck screws, not uncoated staples.

3. Drainage Hole Placement

Cedar is rot-resistant, but standing water accelerates decay at joints and invites root rot. Placement matters more than number of holes.

• Best placement: End walls, not bottom center. Two to four 1/2-inch holes drilled 1/2 to 3/4 inch up from the inside bottom edge create a small internal reservoir while letting excess water escape. This works on both hard surfaces and soil.
• Bottom-center holes alone: Drain fastest but clog when the box sits flat on decking or a patio. Water pools and the bottom boards stay wet. If holes are only on the bottom, always add 3/4-inch feet or risers.
• No pre-drilled holes: Common on decorative boxes. You must drill them. Place holes before filling with soil. For a 36-inch box, drill two holes on each end wall. For a 48-inch box, add two more centered on the long sides, also raised slightly above the base.
• Self-watering planters: Have a false bottom with reservoir and an overflow hole on the side. Do not add extra bottom holes or the reservoir function is lost.

4. Do You Need a Liner for Multi-Season Durability?

Liners help with soil retention and moisture management, but they do not make low-grade cedar last longer on their own.

• Fabric landscape liner (breathable): Recommended for most open-slatted or loosely joined boxes. Keeps soil from washing through gaps, reduces soil-to-wood contact slightly, and allows water and air through. Does not trap moisture against wood. Replace every 2-3 seasons when it tears.
• Plastic liner or heavy poly sheeting: Only useful if perforated at the bottom with drainage slits or holes that align with the box’s drain holes. A solid, non-perforated plastic liner traps water against the bottom boards and accelerates rot at the base – a common cause of early failure.
• No liner: Works fine for tight-jointed, thick cedar boxes if you use a coarse, well-draining potting mix. You will get fine soil staining on a deck during the first few waterings until particles settle. Adding a 1-inch layer of coarse gravel is not needed and adds weight; fabric is lighter and more effective.
• For vegetables: Choose untreated cedar and a food-safe fabric liner. Avoid pressure-treated liners, creosote, or reclaimed wood of unknown treatment.

Spec Comparison: Common Cedar Planter Box Sizes

This table uses typical specs for solid Western Red Cedar boxes sold by established makers such as CedarCraft, Gardener’s Supply Company, Greenes Fence, and Real Wood Products. Capacities are for interior dimensions filled to 1 inch below the rim.

Best Cedar Planter Box by Situation

Match the box to where it will live and how you will use it, rather than just price.

Best for Small Decks and Balconies: 36-Inch Compact Box

If space and weight are limited and you grow herbs, greens, and strawberries, a 36 x 14 x 10-inch box is the most efficient. It fits through standard doorways, stays under 120 lbs when watered, and can sit on a deck bench or on 6-inch risers. Choose tight-knot Western Red Cedar with end-wall drainage and a breathable fabric liner to prevent soil washout onto decking. Market range typically $90-$180 for this size in cedar.

Best for Vegetables and Multi-Season Durability: 48-Inch Standard Box in Clear Heartwood

For tomatoes, peppers, and root vegetables, depth and wood grade are decisive. A 12-inch deep clear heartwood box with 3/4-inch boards will not bow under saturated soil and will outlast knotty sapwood by 4-6 years. Look for models with integrated feet and raised side drainage. Expect to add a fabric liner only if joints have gaps larger than 1/8 inch. Market range typically $160-$320 depending on board thickness and joinery.

Best for Ground-Level Gardens and Poor Soil: Elevated Self-Watering Cedar Planter

If your native soil is heavy clay or contaminated, an elevated legged cedar planter with a reservoir keeps roots out of ground soil and reduces watering frequency by 30-40% in summer. These use a perforated false bottom and side overflow, so watering is via a fill tube. Cedar provides the exterior durability while the internal food-grade plastic tray holds moisture. Better for gardeners who travel or cannot water daily, but heavier and not ideal for windy upper decks.

Best Budget Option That Still Lasts: White Cedar or Tight-Knot Kit with Added Feet

If clear Western Red Cedar is over budget, a white cedar kit with 5/8-inch boards and minimal sapwood is a sound compromise for annuals and flowers, often $60-$120 for a 36-inch box. Longevity depends on aftercare: elevate with aftermarket cedar feet, ensure drainage holes are raised, and apply a penetrating exterior oil rated for garden use, not film-forming varnish which peels.

Durability and Ownership Realities: What Actually Fails First

Cedar planter boxes do not rot evenly. Knowing the failure points helps you extend life to 10+ seasons.

• Bottom boards and lower 2 inches of side walls go first. They stay damp longest. Elevation on feet, raised drainage, and pulling boxes 1/2 inch away from walls for airflow matter more than liners.
• Corner joints loosen from freeze-thaw. Soil expands when wet and freezes. Screws in end grain work loose. Tighten screws each spring and avoid overfilling with dense garden soil instead of potting mix.
• Wicking into end grain. Unsealed end grain absorbs water like a straw. If the maker did not seal it, brush one coat of raw linseed oil or a plant-safe cedar oil on end grain only, not the interior soil-contact faces.
• Soil compaction. After two seasons, peat-based mixes break down and stay soggy at the bottom, accelerating rot. Replace or refresh the top 50% of mix annually and dump and fluff the entire box every 2-3 years.
• Common mistakes: Lining a box with solid plastic without drainage slits, setting a flat-bottom box directly on a deck without risers, using topsoil or compost alone without perlite or bark for drainage, and leaving boxes full of saturated soil over winter in freezing climates. In zones with hard freeze, empty annual boxes after the first frost, scrub, and store under cover or cover with a breathable tarp.

Easy End-of-Season Maintenance (15 Minutes Per Box)

• Remove spent plants and top 2 inches of soil. Scrub interior with stiff brush and water – no bleach on cedar.
• Check drainage holes for soil plugging, clear with a dowel.
• Inspect bottom for soft spots. If wood feels spongy, flip boards if screws allow, or plan replacement next season.
• For winter storage, place scraps of wood under the box to keep it off concrete, which holds moisture all winter.

Decision Matrix: Quickly Map Your Needs

Worked Calculation: How Much Soil Do You Actually Need?

Do not order by exterior size. Use interior dimensions.

Example: 48″ x 16″ x 12″ box with 3/4″ walls: Interior is about 46.5″ x 14.5″ x 11″ deep filled to 1″ below rim = 46.5 * 14.5 * 11 = 7,417 cubic inches / 1,728 = 4.29 cubic feet. That is about 32 gallons.

Potting mix is sold in 1.5 and 2 cubic foot bags (compressed). You will need three 1.5 cu ft bags or two 2 cu ft bags plus a small top-up bag. Cost estimate at general market ranges: $18-$35 per 1.5 cu ft bag for quality potting mix with bark and perlite, so $55-$105 to fill one large box initially. Replacing half the mix annually costs about half that. Factor this ongoing cost – soil costs more over 5 years than the cedar box itself in many cases.

Frequently Asked Questions

Should I seal or stain the outside of a cedar planter?

Optional, but it slows graying and surface checking. If you do, use a penetrating, plant-safe exterior oil or water-based stain labeled for garden beds, applied only to the exterior and end grain. Do not seal the interior where soil contacts wood with film-forming polyurethane or deck stain – it will trap moisture and peel.

Do cedar planter boxes need feet even on soil?

Yes. Even 3/4-inch feet or 2×4 runners prevent the bottom from sitting in puddled water and extend life by years. They also deter ants and slugs from nesting underneath.

Can I leave soil in the box over winter?

In mild climates yes, if drainage is clear. In freezing climates, saturated soil expands and stresses joints. For boxes smaller than 36 inches, empty and store. For large permanent boxes, reduce moisture by stopping watering after frost, cover to shed rain, and keep drain holes open.