I’ve tested solid copper rings which I made from some spare copper roofing strip. Did it work? Yes and No; the difference is oxidation. As it happens most of my slug and snail problems are not pot related but allotment related. For that the boy and I have come up with a handy solution that will re-use plastic with electric guitar insulating tape AND provide protection to all of our allotment seedlings this year (in particular sunflowers, runner beans and squash): RECYCLE PLASTIC AND MAKE YOUR OWN COPPER RINGS! The attention to detail in this study, and the use of the leaf area meter, lets us be more precise and confident in the results." What’s next for slug and snail research?

But Dr Hayley Jones, entomologist at the RHS and lead researcher, said: “With the likes of eggshells, barks and mulch so far proving no discernible deterrent to slugs and snails, we would recommend using proven formulas like nematode biological control if the damage is just too much to bear.” While this research hasn’t shed any light on what you can do to obstruct slugs and snails, it has at least shown that these barriers can be unreliableand ineffective. As members of the Mollusca group of animals, slugs and snails use Hemocyanin proteins in their blood to transport oxygen around their bodies ( whereas we mammals use iron based Hemoglobin). These Hemocyanin proteins contain two copper atoms. This makes all molluscs very sensitive to the ingestion of additional quantities of copper. Too much copper and it prevents oxygen from moving around their bodies and they eventually die, unless they flee to safety.Copper pennies and wire do not seem to work. Most products on the market are a type of copper foil or copper tape so this might work better and in fact some people suggest that a wider strip is better than a narrow strip. Copper is a known poison for many organisms and some copper chemicals are used to disinfect and kill organisms. It seems to make sense that copper tape or copper wire would have the same effect. If you think about this for a minute you will realize this can’t work. Most homes in North America use copper pipe to deliver water in our homes. If it were toxic – would we be using them? I am not a chemist but guess it is due to some kind of ion exchange or electron donation. My guess is that something similar is taking place between the bright copper and the molluscs. Roofing metals are chosen for the job because their oxides adhere to their surface and are chemically inert under normal atmospheric condition. Knowledge of this fact is what lead me to triy the experiment in the first place. The RHS also plans to test alternative control methods, such as beer traps, and is currently working with BASF to investigate ways to combine scientifically proven control methods into pest management strategies. Help us do more research Copper sulphate is made by combining copper alloy with sulphuric acid. Whilst sulphur dioxide emissions from power stations have dropped enormously in Western Europe since the 1980s, there is still enough in the atmosphere for rain to contain traces of sulphuric acid. In certain places within the UK you will be receiving higher doses of sulphuric acid in your rain than others. What happens when this acid rain lands on copper alloy tape on your outdoor plant pots? It makes trace amounts of copper sulphate which runs down your pot and into the soil. I therefore put it to you that as the copper tape weathers, in some areas it releases traces of copper sulphate which makes it even more potent, especially on more porous terracotta pots that can hold onto the copper sulphate. If you live in a city there’s probably more chance of copper tape having this effect than if you live in the countryside. I can’t prove that it exists but it would seem logical.

Lettuces planted in the ground were found to be more susceptible to slugs, with 5.7% of each eaten on average. This compares to just 0.2% of those in pots, which, despite this advantage, yielded less crop.

What does it all mean?

Encourage their natural predators into your garden by creatinga haven for wildlife, such as birds and frogs.

The green patina developed on copper metal over time is a copper carbonate salt and could be toxic. As existing lab studies have shown some of the barriers work, and as other experiments by Hayley hinted that copper tape could be effective, she’s not ruling the barriers out completely. She hopes to run the study again ona different slug population and different soil type at RHS Garden, Harlow Carr in 2019. My criticism of your comments on ‘Electrical current’ as it related to the use of copper is that it represented a deductive approach not an empirical one. Things often fail or succeed for reasons other than we anticipate. There is no substitute for testing. I imagine barrier efficacy might depend on the width of the barrier and skinnier tapes might be less effective barriers than 5″ of mesh. I have yet to try using any other type of mesh (steel, aluminum) but if I get bored that might be a fun experiment. I also imagine in addition to whatever theoretical chemical/electrical property copper has that slugs don’t like, there is likely a mechanical component because irregular wire loops might be irritating to ooze across and there may be some variability in effect based on the size/configuration of the wire in the mesh. If I go out at night I will usually see 2-3 slugs oozing circles around the bottom of the barrier but not crossing it. I have seen a slug or two successfully cross it, but it’s rare. If I had to guess I would say I get about 1/20th -1/200th the slug prevalence I used to previously high slug traffic areas I have since “protected”. (tough to say because I am too lazy to count, and I can’t tell how many slugs crossed the barrier vs just live on the other side)If you’re using any of these five home remedies to deter slugs and snails, consider carefully whether they are making enough difference to be worth the investment. Copper DOES work as a slug and snail barrier if the percentage of copper alloy is high enough and the width is in excess of 4 cms. Don’t waste money on any of the other ‘gardening’ products tested above and be cautious of using anything else that comes in a similar sized box ( or from a matching production line…).

The most humane way to get rid of slugs? Hayley said: “Collect the slugs by hand - the best time to catch them is at night, and either release them at a local wood or pop them in your freezer before binning them My older planters have 6 month old copper mesh barriers and I have yet to notice any obvious decrease in effectiveness with oxidation/dirt, but if there down the road maybe I can mitigate it with a firm wire brush scrub. Jeff Gillman, one of the Garden Professors, commented “When I’ve tested copper the slugs seemed to have a slight preference for not crossing it, but would if that was what they need to do to get where they were going. I’d call it a mild repellant” . I think this is a good summary. Slugs will not go out of their way to cross copper in tape form, but it is not a fool proof solution. I have had a respectable amount of success in slug deterrence using copper mesh as a slug barrier on the outside of wood planters. The mesh is about 5″ wide, which is wider than any of the copper tapes I have seen for sale, and it’s easier to work with compared to the super delicate copper tape I tried, the tape I tried, and it’s easy enough to reuse (although not adhesive on it’s own)These methods were tested on 108 lettuces sown in pots and raised beds at the RHS field research facility in Wisley. After six weeks, the leaves of each harvested lettuce were examined to calculate damage. But wool pellets and pine bark did have one clear benefit: by acting as a fertiliser and mulch, they helped lettuces yield a 50% bigger crop. You may be correct. As I said I am not a chemist. Although I’m not sure that ‘Conducting current’ is the same as ‘exchanging an electrical charge’. But who really cares. The issue is whether or not it works and if so, under what conditions.