Coffee grounds scattered around plants repel slugs, snails, and other pests.
Contested
Coffee grounds don't reliably repel slugs or other pests — the idea comes from caffeine being toxic to slugs in the lab, but used grounds carry far too little to work as a barrier, and trials don't back it. Use beer traps, night hand-picking, or iron-phosphate bait for slugs; compost the grounds or spread a thin mulch for the organic matter.
What is actually known
This comes from a real finding — caffeine at high concentration is toxic to slugs and snails, and a caffeine spray suppressed them in one study. But used coffee grounds are not a caffeine barrier: brewing removes much of the caffeine, a scatter of grounds delivers nowhere near the concentration that study used, and field trials do not find grounds reliably deter slugs. The grounds can also dry into a water-repellent crust that does more for the myth than for the plant. As a thin mulch or a compost input the grounds are fine — a modest slow nitrogen source — but as a pest barrier they are not the tool they are sold as. (The separate claim that grounds acidify soil is its own belief, B-006; the eggshell version of the sharp-barrier idea is B-005.)
Evidence: not yet confirmed against its 1 source.
what this rests on - one pointer
caffeine is toxic to slugs at high concentration but used grounds deliver far less; field trials do not support grounds as a slug or pest barrier; extension consensus
When would that grow at your place? →
Cite this page
Milpa Gardens. "Coffee grounds scattered around plants repel slugs, snails, and other pests." Evidence grade: Contested. https://milpa.garden/beliefs/coffee-grounds-slugs-coffee-grounds-pests/
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