Carboard has been a popular material to smother weeds in gardens for a long time. It blocks light, oxygen, and rain more effectively than many inches of wood chips. Some people wonder, though: is it safe? Let’s set the most alarming rumours to rest:
Cardboard is full of lye: Lye is a natural product of the wood-pulping process, but what remains in cardboard is both safe and quickly broken down.
Cardboard contains PFAS: Truthfully, everything in our world does. Plants take these chemicals up from the environment, so trees contain them before their wood is even pulped. Unless cardboard is waterproofed, manufacturers aren’t adding them. Since mulching with cardboard requires less plant matter overall than mulching with wood chips or other materials does, the total amount of PFAS can ultimately be less.
You don’t know what’s in the ink or glue: We do! In standard non-glossy black-on-brown printed boxes, the ink is soy based and the glue is starch based.
To use cardboard safely, avoid glossy surfaces, colour inks, and any cardboard that’s been treated to be water resistant (you’ll know because water beads and rolls off it). Remove staples, tape, and labels…and enjoy some peace of mind!
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