Safe hardscape is chemically inert or known-safe for enclosed plant systems, structurally stable when wet, and free of salt, varnish, pressure-treatment and unknown finishes.
Never use painted, pressure-treated, cedar or pine with strong resins, or oily barbecue wood. Seashells and beach wood may add unwanted salt.
Resin ornaments must be fully cured and labelled aquarium- or terrarium-safe. A vinegar test screens carbonates only — it does not prove a rock is free of all toxins.
