When selecting finishes for urban planter boxes that will endure full sun exposure all day, the primary considerations should be UV protection, moisture resistance, and material compatibility. For wooden planters, penetrating oil-based finishes typically outperform surface coatings because they allow the wood to expand and contract without cracking the protective layer.
The most recommended options include:
- Penetrating exterior wood oils (like Penofin or Messmer's UV Plus) that contain UV blockers
- Semi-transparent oil-based stains that penetrate deeply while allowing wood grain to show
- Specialized planter box finishes labeled as food-safe if growing edibles
- Marine-grade spar varnish for maximum protection (though requires more maintenance)
For cedar and redwood planters, choose finishes specifically formulated for these softwoods. Apply two thin coats, allowing complete drying between applications. Reapply annually for optimal protection against sun damage and moisture penetration. Avoid solid color stains on rough-sawn wood as they can trap moisture against the wood surface.
Proper surface preparation is crucial - ensure wood is clean, dry, and free from previous finishes before application. Consider finishes with mildewcides in humid climates, and always follow manufacturer's directions for temperature requirements during application.