COPPER 2: 14 July 2003
RS e-mails: I read of people keeping slugs and snails at bay using copper wire but to date I am having no such luck. I have put a loop of such wire around some sunflower seedlings only to find them eaten. The wire I'm using has been salvaged from old electric cabling striped bare. Is this the correct wire to use? I don't want to use slug pellets if I can help, so hope you can help.
RS enlarges, in a subsequent e-mail: With regards to the copper I'm using as an antislug weapon, I'm not sure of the gauge but it's about 1.5mm. I make a circle of it winding it around itself 3 or 4 times just big enough to go around each plant, which is about 2 ins across. it touches the ground as far as I can tell all the way and nothing can get underneath. I read of other people having success using it and wonder why I don't seem to.
R J Harris responds: "Mr S must change his material. My own trials have shown that unlike what was once believed, copper wire extracted from domestic electric cabling is not thick enough to do the job -- even when several strands of it are twisted together to make a thicker barrier. It does not offer a sufficient width of the metal for the slug or the snail to have to crawl across."
The ideal, Mr Harris has found, is copper tubing of the kind that is used in domestic hot-water systems. The tubing he uses is never bought: the head gardener maintains special relations with his neighbourhood's plumbers, and he is ever alert for skips containing builder's rubble.
The advantage of the tubing is to be found in its diameter and its rigidity.
"It lies flat on the top of the soil, as wire cannot -- especially wire that has been kinked and bent during the insulation-stripping process. So nothing can crawl beneath it. The surface of the soil must be flattened first of all, of course, and that applies no matter what form of copper is used as a slug/snail barrier. Use the flat of a shovel. Or put down a board and kneel on it for a moment or two.
"Then there is the width of the tubing. This offers what I believe is the least width of copper if the slime that the creatures put down as they move is to convey an uncomfortable enough impression. Bear in mind that it is this slime, really, that warns the animals to go back the way they came. It is their sensor. It conveys to them everything they need to know in order to survive. It tells them that an unacceptable quantity of copper is ahead, and they hate the sensations that prolific copper gives to them via their slime."
Mr Harris improves upon his copper tubing by first of all flattening it with a lump hammer.
"This increases its width. It gives the slug even more copper to have to crawl over to get to the plants."
Bearing in mind the black keel slug's ability to travel beneath the surface of the top soil, the head gardener lays down not one but two or three encirclements of flattened copper tubing.
"Position the inner-most ring -- or square, as it must be, because you cannot bend the tubing, flattened or not, to form a circle -- no more than about two inches or four centimetres from the plant.
"That way, neither slug nor snail should be able to get through -- provided that the copper isn't bridged by earth or vegetable matter, is continuous and touches the ground for the whole of its length."
