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Why used coffee grounds may be doing your plants more harm than good

We are often told to add used coffee grounds to garden soil to perk up plants. But the science doesn’t support this, says James Wong

By James Wong

14 June 2023

R126CH Unrecognisable woman in casual clothing holding a box of used coffee ground to use as compost in her garden.

DGLimages/Alamy

WANDERING around an achingly cool San Francisco coffee shop a few years ago, I was fascinated to see huge, open-topped barrels filled with used coffee grounds and a sign saying they were free for customers to scoop into recycled bags and take home to perk up their plants. I realised that we had reached peak hipster.

Indeed, the claim that coffee waste dramatically boosts plant growth has been a staple of organic gardening books since at least the 1970s, and seems to be seeing a modern renaissance. Proponents everywhere wax lyrical about how the spent grounds are not only rich …

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