At our planter box factory, the answer is not a single chemical. Our main outdoor range is pressure-treated with arsenic-free, waterborne preservatives: ACQ (alkaline copper quaternary) and copper azole (CA). We choose between them based on the wood species, target market, and the amount of ground contact the planter will see. For boxes that sit on a patio or deck, we typically specify an above-ground treatment level. For larger raised beds or planters in direct soil contact, we use a stronger soil-contact retention level. The treatment is applied in a closed pressure cylinder, followed by controlled drying, so the timber is stable before it is cut, sanded, and assembled.

We do not use CCA (chromated copper arsenate) for residential garden planters. ACQ and copper azole are widely accepted alternatives because they protect against fungal decay, termites, and moisture damage without adding arsenic to the wood. That said, no treated wood should be treated as a cutting board or a direct food-contact surface. For edible gardens, we recommend a liner or barrier between the timber and the soil, especially for copper-sensitive plants.

We also produce preservative-free lines. Western red cedar, black locust, larch, and thermally modified ash offer natural rot resistance without chemical treatment. They cost more or have different maintenance needs, but many customers prefer them for organic gardens or visible architectural features.

Our factory also applies water-repellent finishes and stains, but these are not preservatives. They slow moisture movement and improve appearance. Every batch is checked for moisture content, penetration, retention, and traceability, and we adapt to AWPA, EN, or local requirements. In short, our planter box factory uses ACQ and copper azole as its primary wood preservatives, plus natural and thermal options, and never CCA for home garden planters.