Copper tape for slugs

The claim

Copper tape around a pot or bed gives slugs an unpleasant electrochemical sensation they will not cross.

What the evidence actually shows

This entry is worth reading carefully because the evidence genuinely conflicts, and the honest answer is a split one.

Controlled experiments published in Crop Protection found copper foil delayed but did not prevent Arion vulgaris crossing, and that barrier width of 3, 4 or 6 cm made no difference. In semi-field validation there was no difference in slug damage events between pots with and without copper foil. The same study found waterglass - sodium silicate - fully blocked passage and halved damage events. So the barrier concept works; copper is simply not the material that does it.

The RHS lettuce experiment reached the same practical conclusion: copper tape rings produced no measurable reduction in leaf damage over six weeks. Notably, the RHS states that lab studies have shown some barriers working and that its own earlier experiments had hinted copper tape could be effective.

Against that, UC IPM still recommends copper flashing and vertical screens at least four inches tall, buried a few inches, and states slugs will not cross copper unless the surface is fouled with debris or becomes heavily oxidised.

The likely resolution

That fouling caveat probably explains the whole disagreement. Clean copper in a laboratory deters slugs. Copper in a garden oxidises within weeks and collects soil, algae and organic film. The material that works is not the material that remains after a month outdoors. Which means the honest verdict is: works briefly, fails in service, and the failure is invisible because the tape is still there.

What to do instead

If a physical barrier is wanted, sodium silicate performed in controlled testing. Otherwise iron phosphate baits, trapping and shelter reduction. If you already have copper tape installed, clean it, and do not treat it as the whole strategy.