What's inside
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Spring is a good time to build a planter: boards are easier to find, and you can finish and assemble the box before planting. The main choice is not simply “which wood lasts longest?” It is how much you want to spend, whether you want to avoid chemical preservatives, and how much maintenance you’ll accept. A planter that drains well and dries between rains can outlast a more expensive one built to hold water.
Contents
Start with the planter’s size and exposure
Measure the finished box before buying lumber. A common raised planter is about 18 to 24 inches deep and 4 feet long, but a smaller patio box may need only 10 to 12 inches of depth. Longer boxes put more pressure on the sides when filled with wet soil; use thicker boards or add corner posts and a brace rather than assuming thin boards will hold.
Sun, rain, and contact with soil matter. A box under a roof, raised on feet, and allowed to drain has an easier life than one sitting on damp ground. End grain absorbs water quickly, so board ends and joints are often the first places to soften or split.
Compare common board choices
| Wood | Typical trade-off | Good fit |
|---|---|---|
| Cedar | Naturally decay-resistant, light, and easy to work; usually costs more than pine. It can still split, check, or decay if kept wet. | Planters where lower maintenance and untreated wood are priorities. |
| Redwood | Durable and workable, but price and availability vary by region. Lower grades may contain knots or defects. | Long-lived builds when suitable boards are locally available at a reasonable price. |
| Pressure-treated lumber | Often economical and resistant to decay; can be wet, heavy, and prone to twisting as it dries. Cut ends need attention. | Budget-conscious outdoor boxes, especially where the lumber will not touch edible plants or soil directly. |
| Untreated pine or spruce | Inexpensive and easy to find, but usually the shortest-lived choice outdoors, particularly at soil level. | Temporary planters, protected locations, or a first build where replacement is acceptable. |
For a straightforward untreated build, compare local prices for cedar boards for raised beds. Stock dimensions and grades differ, so check the actual board rather than assuming every piece sold as cedar is clear or straight.
Choose by budget and intended use
Cedar is a practical middle ground for many home planters: it resists decay better than ordinary untreated pine without requiring a coating to provide that resistance. It is not indestructible, and paying extra for clear, knot-free stock rarely makes sense for a rustic box. Reject boards with soft spots, deep splits, or knots near a fastener line; small sound knots are usually a cosmetic issue.
Pressure-treated lumber can be a sensible choice for a utility planter, especially if the box is isolated from soil with a suitable liner and the lumber is approved for the intended use. Follow the label and local guidance, and do not burn offcuts. If you prefer to keep treated wood out of an edible garden, choose untreated durable wood or use a separate liner that does not hold water against the boards.
Untreated pine is fine when cost matters more than longevity. Use it for a season or two, or for a box under an eave that can dry quickly. A coating may slow wetting, but it does not turn pine into rot-resistant lumber. Repainting and eventual board replacement are part of the bargain.
Inspect boards before buying
Lay each board on a flat surface and look down its length. Avoid severe bow, twist, or crook, which makes square corners difficult and can open joints later. Check both faces and edges for cracks, decay, and loose knots. For side boards, common thicknesses around ¾ to 1 inch work for modest boxes; taller or longer walls benefit from thicker material or internal supports.
Buy a little extra length to trim damaged ends and square the cuts. For a 4-foot box, do not assume a nominal 4-foot board will provide a full 48 inches after trimming. Read the listed actual dimensions, and lay out the cut plan before checkout.
Build the box to drain and dry
Leave the bottom open over soil, or fit slats with roughly ¼ to ½ inch gaps over a stable frame. If the planter sits on a patio, include drainage holes and raise it on feet so water can escape rather than pooling beneath the box. Do not seal every seam in an effort to make the planter watertight; standing water speeds decay.
Use corrosion-resistant exterior screws, such as galvanized or stainless steel, sized to suit the lumber thickness. Predrill near board ends to reduce splitting, particularly in cedar. A simple box with corner posts is easier to keep square than boards joined only edge-to-edge. For a wide, soil-filled box, add a cross-brace or tie between opposing walls to limit bowing.
Keep wood-to-soil contact down where practical: feet or pavers help, and a replaceable liner can separate soil from the sides. Make sure the liner has drainage openings and does not trap water against the wood. If finishing the outside, choose an exterior coating labeled for the intended exposure and follow its cure time; finish cannot compensate for poor drainage.
Time the build for spring conditions
Let wet lumber dry enough to handle and fasten cleanly, but do not leave it uncovered for weeks in a muddy yard. Store boards flat with spacers between layers and cover the top while keeping the sides ventilated. Assemble on a reasonably level surface, then check diagonals: equal measurements mean the box is square.
Before adding soil, inspect screws, corners, and drainage. Recheck after the first heavy rain and again near the end of the growing season. Early signs of trouble include dark, persistently damp patches, soft end grain, loose fasteners, and sides beginning to bulge. Replace a damaged board before the box is full; repairing it under wet soil is harder.
For most gardeners, the best purchase is the least expensive board that matches the expected lifespan and exposure. Cedar suits a durable untreated planter, treated lumber can make sense for a low-cost utility build when used appropriately, and pine is an honest choice for a temporary or sheltered box. Good drainage and careful board selection matter more than a premium label.