Your concern about pests is very valid for any gardener. While no material is a complete force field, certain planter box materials do offer inherent properties that can deter insects better than others, reducing your pest problems.
The top choice for natural insect resistance is Cedar or Redwood. These softwoods contain natural oils and tannins that repel common pests like ants, termites, and some moths. Cedar is particularly known for its durability and pest-repelling scent, which fades slowly over time.
Metal planters, especially galvanized steel or aluminum, provide a smooth, hard barrier that insects like borers or cutworms cannot penetrate. They offer no organic material for pests to feed on or nest in. Ensure proper drainage holes are raised or protected to prevent creating entry points.
Fiberglass or composite planters are another excellent option. Their non-porous surface denies insects hiding spots and makes it difficult for them to gain a foothold. They are also inert and do not provide food for pests.
Conversely, avoid untreated softwoods like pine, which rot quickly and attract pests. Standard terracotta or ceramic is pest-resistant but can develop cracks that harbor insects. Plastic planters can be safe but may degrade in sun, creating crevices.
For best results, combine a pest-resistant material with good practices: use fresh, sterile potting mix, ensure excellent drainage to avoid fungus gnats, and clean planters between seasons. Choosing cedar, metal, or fiberglass creates a strong first line of defense, leading to a healthier garden with fewer chemical interventions.