Wood mulch is a documented ignition source for home fires. A discarded cigarette, an ember from a grill, even reflected sunlight can smolder unnoticed in dry bark for hours before flames erupt. The NFPA reports thousands of landscape mulch fires across the U.S. every year — roughly half traced to discarded smoking materials.

Bark and shredded wood feed termites and carpenter ants. "Artillery fungus" shoots black spores onto siding and cars. Sour mulch can kill the very plants it's supposed to protect.

Much of the dyed wood mulch sold at big-box stores is ground-up pressure-treated lumber. Over years, those preservatives leach into the soil — the soil where kids play, pets dig, and tomatoes grow.