Coffee grounds scattered around plants repel slugs, snails, and other pests.
Coffee grounds scattered around plants haven't been shown to repel slugs or other pests. The idea comes from caffeine, which does kill slugs in a strong enough soil drench, but used grounds hold very little of it. Use beer traps, hand-pick at night, or put down iron-phosphate bait; put the grounds in the compost.
What is actually known
This comes from caffeine. Oregon State reports that a 1% to 2% solution drenched into soil drove slugs out and killed them by caffeine poisoning, and it promotes liquid coffee as a slug killer. But that is a drench. Used grounds keep only small amounts of caffeine, and there is no published evidence that coffee grounds repel or kill any garden pest. Grounds are finely textured and compact easily, so on the surface they can dry out and shed water unless covered with leaves or bark. They are a fine compost ingredient and soil amendment. (The separate claim that grounds acidify soil is checked on its own page, and so is the claim that crushed eggshells deter slugs.)
The evidence
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
There is no published evidence that coffee grounds will repel or kill any garden pests. Nor is there any science-based information on their ability to attract either pests or beneficial animals like earthworms.
Spent coffee grounds can be used as a soil amendment and compost ingredient, while liquid coffee acts as an effective slug killer.
Crushed egg shells or coffee grounds have not been shown to be effective deterrents.
It is the trap that will kill them, not just the bait.
Check another piece of garden folklore ›
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/
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
See this claim in the planner’s evidence page
Report a problem with this claim
How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Contested here means nothing we found supports it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.