It is one of gardening’s most repeated tips: put copper tape around a pot and the slugs will stay out. The explanation sounds convincing—the slug’s mucus supposedly reacts with the metal and gives it a small electric shock.

That satisfying explanation is exactly why the advice survives. It sounds like a reason. Why check something that already makes so much sense?

Except people have checked.

In the Lab, It Works

Place a slug in front of a clean strip of copper and it hesitates, retreats, or goes around. The aversion is real and measurable.

In the Garden, It Does Not Hold Up

The Royal Horticultural Society tested copper barriers under real-world conditions and found no measurable reduction in damage. A study published in Crop Protection reached the same conclusion: copper delays a crossing but does not prevent it, and the final number of damaged plants is the same with or without copper.

Why the Difference?

There are three ordinary reasons:

• A barrier is useless if the slug is already inside it. Slugs spend the day in the potting mix, not outside the pot.
• Copper oxidizes. Last year’s tarnished tape is no longer the clean copper used in the lab.
• A leaf droops over the rim and suddenly there is a bridge. Slugs are patient.

What the Evidence Supports

• Nematodes (Phasmarhabditis hermaphrodita)—genuinely effective, but they require soil above 5°C, reapplication every six weeks, and they are expensive.
• Beer traps—they certainly kill slugs, but they also attract them. A trap protects its immediate surroundings, not an entire garden.
• Hand-picking after dark, flashlight in hand. No technology at all, and it still removes the most slugs in a single evening.

Copper is not a scam. It is a genuine laboratory observation that simply did not survive the move outdoors.

Keep the tape if you already have it. Just do not rely on it.

What have you tried against slugs? Tell us what worked—but also what did nothing. That is often even more useful to know.

Sources: Royal Horticultural Society — Slugs and snails · Thirty years of slug control using Phasmarhabditis hermaphrodita