What not to fill a raised garden bed with?

Avoid filling a raised garden bed with straight topsoil, fresh wood chips, pure compost, gravel as a drainage layer, or treated lumber debris — each either compacts, robs nitrogen, drains poorly, or introduces toxins that harm plant roots and soil biology.

Raised garden beds fail most often because of what goes inside them, not the structure itself. Straight topsoil compacts under irrigation and blocks root penetration. Fresh wood chips and uncomposted wood scraps pull nitrogen out of the soil as they break down, starving plants. Pure compost holds too much moisture and can cause root rot. Gravel drainage layers — a widely repeated myth — actually create a perched water table that keeps the soil above it wetter, not drier.

• Fresh uncomposted wood materials deplete available soil nitrogen for 6–12 months during decomposition.
• A gravel drainage layer in a raised bed creates a perched water table, increasing moisture retention above the gravel, not reducing it.
• Pressure-treated lumber debris and construction fill can leach arsenic and other compounds into the root zone of edible crops.
• Straight topsoil compacts to roughly 50% of its original volume within one growing season when used alone in a raised bed.
• AmazStove raised garden beds use an open base design — no solid floor — which requires a well-draining fill mix, making fill composition especially critical to performance.