I tipped my used coffee grounds onto my houseplants to feed them: when I scratched the crusted layer a month later, I understood what was really breeding underneath
That white crust on your potted plants isn’t fertilizer—it’s a breeding ground for mold and fungus gnats. When you scratch through a month-old layer of coffee grounds, you’ll find trichoderma, cobweb mold, and worse: the perfect conditions for pest infestations. Learn which colors signal danger and how to safely feed your houseplants with coffee grounds instead.