Best choice overall: Western red cedar -- naturally rot-resistant, safe for edible plants, lasts 15-20 years. Budget: untreated pine (3-5 years). Premium: redwood or black locust. Longest lasting: composite (20+ years).
Why Wood Choice Matters
The lumber for raised garden beds holds hundreds of pounds of wet soil while in constant contact with moisture. Use boards at least 2 inches thick -- thinner lumber warps under the weight of wet soil. Two key factors: soil safety (no chemical leaching near edible plants) and rot resistance (ground-contact wood decays far faster than above-ground applications).
Western Red Cedar -- The Top Choice
Cedar contains natural oils (thujaplicins and phenolic compounds) that resist rot, fungal decay, and wood-boring insects without chemical treatment. Completely safe for edible vegetable gardens.
| Property | Cedar Performance |
|---|---|
| Rot resistance | Excellent - natural oils protect without chemicals |
| Insect protection | Good - naturally repels termites and borers |
| Soil safety | Excellent - no chemicals, safe for edible plants |
| Typical lifespan | 15-20 years moderate; 7-12 years high-moisture |
| Cost | $3-$6 per board foot |
Redwood
Matches cedar for natural rot resistance with a distinctive deep reddish colour. Equally safe for edible plants. Prioritize heartwood -- it contains the protective tannins. Look for FSC-certified redwood.
Pressure-Treated Wood -- The Facts
- Old CCA treatment (pre-2003): contained arsenic -- identified by green tint -- do NOT use near edible plants
- Modern ACQ/MCA treatment (post-2003): copper-based, EPA-approved for residential use, considered safe for raised beds
- Extra precaution: line the interior with food-grade plastic for complete certainty
Untreated Pine -- Budget Option
Safe for edible plants but only lasts 3-5 years in direct soil contact. Extend life by applying raw linseed oil (food-safe) to exterior surfaces and lining the inside with plastic.
| Material | Lifespan | Maintenance | Cost |
|---|---|---|---|
| Cedar | 15-20 years | Occasional oil | Medium |
| Redwood | 15-20 years | Occasional oil | Medium-High |
| Composite | 20+ years | None | High |
| Untreated pine | 3-5 years | Frequent sealing | Low |
Best Choice by Climate
Humid and rainy: Cedar, redwood, or black locust -- natural oils fight constant moisture.
Dry, high-sun: Cedar or composite. Apply food-safe UV-resistant sealant.
Freeze-thaw: Use thick boards (2"+ ) and ensure excellent drainage.
Building Tips
- Minimum board thickness: 2 inches
- Use galvanized or stainless hardware -- regular screws rust quickly in constant moisture
- Line with hardware cloth (half-inch mesh) at the bottom to block gophers while allowing drainage
- Build in modular sections -- easier to repair one section than replace an entire bed