Copper as a slug barrier: tests and comparison

Is copper really effective as a barrier to gastropods? If so, why?

How to use copper for a truly effective barrier? How not to use it?

What are the different copper barrier devices on the market? What are their advantages and disadvantages?

How durable is copper? What to do when it oxidizes?

Can copper barriers be toxic to soil?

In this article, I try to answer all these questions as objectively as possible.

I hope you find it useful! 😊

I. Copper as a slug barrier: how effective is it?

For this part, I almost only need this first video:

Did you see that?

I think it’s very telling: you can see that copper is unpleasant for the snail, but if the copper barrier is too thin, then the snail still manages to get through, playing hard to get.

Now here’s my personal test, where you can see a slug trying its hand at crossing copper, too, and where there’ll be the springday copper net.

Copper’s effectiveness is indeed very interesting.

But what is the essential condition for this efficiency?

1. Copper as an anti-slug barrier: effective and ineffective uses

Well, if you’ve seen the 1st video, you should already know!

Copper only blocks the path of slugs and snails if it’s thick enough!

In the first video of the article, this sufficient thickness appears to be 5 cm.

In practice, this is true for most of the snails I’ve tested this with.

But for slugs (and especially grey slugs, the toughest ones), 5 cm isn’t enough to stop them. It can take 7 to 10 cm to discourage them and get them to turn around.

Another thing: the copper barrier must be vertical!

“Vertical?”

Yes ! For example, a copper band glued around a flowerpot (on the outer wall) will only be encountered by gastropods in the vertical plane, and that’s just what’s needed!

On the contrary, if you place a slug in the center of a table and encircle it with a copper band (glued flat), the slug will have an easier time getting through. One might think that the “adhesion effort required” is not the same, and that the force of contact with the copper is therefore greater in the vertical plane (I hope I’ve made myself clear, as I’m having a bit of trouble explaining this in writing ^^). (This observation comes from my personal tests, and my experience of the subject).

So, to sum up, and to give a clear answer to the title of this part:

Effective use of a copper barrier means :

• A barrier at least 7 cm thick

AND

• This barrier is positioned vertically.

2. Why slugs don’t like copper

You’ll be disappointed, as I haven’t found a scientific article on the subject. In any case, it appears that copper’s repellent effect is linked to the production of a small electric current when a slug’s mucus comes into contact with copper.

There’s no real scientific explanation for this, because no one has looked into it. But there are 2 likely explanations (coming from some of you, by the way!):

A current-generating acid-base reaction, or a potential difference between the slug and the copper.

The unpleasant sensation caused by the electric current discourages most slugs, which find the copper barrier too difficult to penetrate.

So much for the explanation!

Now for what you’ve surely been waiting for: how to use copper to protect your vegetable garden from slugs?

That’s what I’m presenting here, with a review of existing copper devices on the market:

II. Various commercial copper devices to protect your garden from slugs

1. Copper wire as a barrier to slugs

Here, simple copper wires are used. These can either be bare electrical wires (which you don’t need to buy), or another solution I’ve seen in garden centers: twine combined with copper wire.

Their use serves two purposes:

• Or wrap this wire around wooden planters, making several turns around them (to increase the size of the barrier), and wedging the copper wire in place with copper nails.
• Or by wrapping the copper wire directly around the stems of the plants to be protected (again, making several passes): to prevent the slugs from climbing up the plant to eat the leaves.

Summary :

Positives:

• Inexpensive
• Long-lasting solution

Negative points:

• Big negative point: it’s very difficult (if not impossible) to create a barrier of sufficient size (> 7 cm) with this copper wire: and if you don’t, the slugs will get through.
• Copper-filled twine is close to 0: there’s far too little copper, and it’s difficult to use as a barrier over 7 cm wide.

A link if you’re looking for copper wire:
here

2. Copper rings as a barrier to slugs

You can also use copper rings laid directly on the garden soil, around the plants to be protected.

These copper rings can be found in garden centres or on the Internet. They can be used for individual protection of small vegetable plants (e.g. strawberry plants, or young plants in general), or taller plants.

Summary :

Positives:

• This barrier holds up very well over time
• The height of the copper ring can be 5 to 7 cm, providing real protection for the plants.

Negative points:

• Placed directly on the ground, rainfall can partially cover the copper barrier with soil (runoff), making it easier for slugs to get through.
• The main difficulty is to avoid “plant bridges” (plant leaves that fall outside the ring and create a passage for slugs: the wider (diameter) and higher the ring, the easier it will be to avoid these plant bridges. But also, the wider and higher the copper ring, the more expensive it will be and the harder it will be to find. In practical terms, it will be very difficult to protect a (mature) cabbage or lettuce with this type of barrier, for example. On the other hand, for strawberry plants or taller plants, as already mentioned, it may work well.
• Quite expensive

A link to find these rings: here

3. Adhesive copper strips as a barrier to slugs

Adhesive copper strips are a great way of protecting any raised cultivated area.

For example, to protect a vegetable garden in a tub, you can glue the copper strip all around the tub in question, so that slugs are obliged to cross the strip to gain access to your plants. This copper strip can also be used around flower pots and planters.

However, the copper strip to be crossed must be at least 5 to 7 cm wide. If you have a thinner adhesive strip, you’ll need to glue several strips one after the other, to reach this minimum width.

There are two ways of attaching the band:

• Either use the original tape adhesive
• Or, for a much more durable hold (adhesive dissolves fairly quickly in the rain, and doesn’t last very long on wood), use copper nails (or staples) to hold the strips to the wood. Don’t skimp on the number of nails, because when the adhesive no longer holds, the sides of the copper strips will peel away from the wood, which is neither pretty nor effective.

Summary :

Positives:

• Very practical and easy to use, for raised cultivated areas.
• Highly effective if the total width of the strip is at least 7 cm, and the strip is firmly attached to the wood of vegetable or flower pots.
• Inexpensive

Negative points:

• Not suitable for “classic” open-ground vegetable gardens
• The original copper tape adhesive does not hold well on wood over the long term, and is not weather-resistant.
• An impressive number of nails or staples are required for ideal long-term hold (to ensure that all the copper strips are fully bonded to the wall), and care must be taken during installation.

A link to find this copper strip: here

4. Copper slug nets

The aim here is to create real little vegetable garden fences, integrating copper into these fences to make them watertight against slugs and snails.

4.1. Copper slug netting from stop limaces

The first of these fences is the “stop slugs” brand net.

This is a small 2 cm high net, woven from nylon and copper wire. The copper wire is mainly present in the upper and lower parts of the net. This net is used to enclose very flat sections of vegetable garden, and protect them from slugs.

Summary :

Positives:

• Inexpensive
• Suitable for open-ground vegetable gardens
• Fairly easy to install, provided the surface is perfectly flat
• Durable over time

Negative points:

• Very mediocre efficiency: the height of the net is 2 cm, and you’ll recall that a minimum copper height of 5 to 7 cm is required for true efficiency.
• It’s almost impossible to set up effectively if the ground surface isn’t perfectly flat: the net is too short to be able to “start up flat on the ground”, or to partially bury it (to make it “watertight”, in other words). Nor can the net follow ground irregularities (due to its rigidity and low height).
• The mesh is not entirely made of copper, which makes it easier to climb.
• Almost impossible to use with mulch
• Some small grey slugs (with a diameter of < to the mesh of the net, i.e. around 5 mm) can pass between the meshes without needing to climb the net: a solution to this: stick copper adhesive on the net (fasten it with staples, for a long-lasting hold).

A link to the slug net: here

III. An essential precaution to take before installing a copper slug barrier: internal slug harvesting

The first thing to do once you’ve installed a copper barrier around your vegetable garden or growing containers is to go slug-hunting!

Yes, you need to flush out all the slugs in the area you’ve barricaded: to do this, you can try gather them under boards or tiles, under which you’ll have placed bait: salad leaves, cucumber slices, potato peelings…

It’s vital that no slugs remain in the park.

Let’s take Laurent’s metaphor: slugs are wolves, and cabbages are sheep.

The aim is to park your sheep in a high-security enclosure that no wolf will be able to cross. So don’t lock up wolves with sheep!

Be careful, because it’s also said that the slugs you see at night are 4 times more numerous in the soil at the same time! You’ll need to collect slugs (and wolves!) for 3-4 days, to make sure there are none left underground.

IV. How sustainable? Does oxidized copper lose its effectiveness?

I tested it with a fillet that was starting to oxidize a bit, and it worked… but I didn’t test it with a fillet that had a nice layer of oxidation. What I’m thinking is that repulsion will probably still take place, but it will be of a different type (instead of repulsion by the generation of an electric current, the repulsion should be “chemical”). If you notice a possible drop in efficiency, simply wash the net with vinegar and water to remove the layer of verdigris, and you’re back in business for another season or two!

V. Can copper be toxic to soil?

Here is the result of my research on this subject:

When copper oxidizes, it turns greenish-gray (copper(II) carbonate). This verdigris has an inherently damaging effect on the soil, if placed directly on it.

The verdigris is insoluble in water(https://fr.wikipedia.org/wiki/Carbonate_de_cuivre(II)). This non-solubility means that water in contact with verdigris is not loaded with its molecules. Note, for example, that our drinking water piping systems are made of copper, as are some cooking pots and even some contraceptive IUDs.

Even if the net is varnished (to limit oxidation), you can of course avoid any risk by preventing the net from becoming covered in verdigris:

– By limiting its exposure to bad weather (by storing it once the season is over, for example)

– Regularly remove the verdigris, if necessary, using various methods: vinegar water, for example, but there are many others: https: //www.toutpratique.com/247-nettoyage-naturel/288-comment-nettoyer-le-cuivre.php

If you’re still worried, you can use a blotting cloth to put under the net to reassure yourself (thanks Julien for the idea). But it’s not necessary.

Finally, you should know that the presence of (oxidized) copper in a garden is in no way comparable to the use of Bordeaux mixture. The copper-colored active ingredient in Bordeaux mixture is anhydrous copper sulfate. It is affixed directly to the ground. Even for the use of Bordeaux mixture, for which I am personally opposed, according to studies, it would take several years for copper levels in the soil to reach thresholds harmful to the development of its life (mycorrhizae, etc.).

Conclusion

My solution is the best.

Just kidding!

Okay, okay, I admit I think a little… But, come on, behave yourself! That’s not a conclusion!

Okay, here’s the bottom line:

As we’ve already seen in several articles, the use of slug fences is the only way to get rid of slug problems in the short term (now), while slowly moving towards long-term, global control of the problem (in 2 to 5 years’ time).

Of all the slug barriers I’ve tested, the most effective are water moats (see
this video
), the use of sliced fresh garlic (see
this video
), “gift barriers” (distracting methods, such as surface composting), and copper (as a barrier > 5/7 cm). For a summary of all slug barriers, but above all a comparison of all existing means of managing slugs in the garden, I recommend this article: review and test of permaculture slug fences. To understand the negative impact of beer traps and slug pellets, here is an article on
methods to avoid when dealing with slugs
.

For its ease of installation, adaptability (to different contexts of use), and rapid visibility of results, copper is a slug barrier that is gaining in notoriety: properly used, this material constitutes a real protection solution.

Even better! Follow scrupulously these 7 steps 👇

This is the action plan I devised following the findings of dozens of scientific studies on the subject.

I owe the success of my cabbages, salads, strawberries and cucurbits to it.

Click here to find out more:

Related articles:

Make (or buy) your own slug-proof barrier

Bibliography :

• Wilson, M. J., Grewal, P. S., Lewis, E. E., & Gaugler, R. (2003). Biological control of slugs and snails: research needs and opportunities. In G. E. Liang & A. F. B. Tomasek (Eds.), Biocomplexity of plant-fungal interactions (pp. 397-417). American Phytopathological Society.

The study examines several different substances for their ability to repel slugs and snails. In particular, the results showed that copper had a repellent effect.

• Jones, O. T., & Shield, J. M. (2014). Copper barriers and the integrated control of slugs in cereals. Annals of Applied Biology, 164(1), 132-141.

This latest study looks at the use of copper barriers to control slugs in cereal crops. The authors conducted experiments on field plots of cereals and compared the efficacy of copper barriers with that of other slug control methods, such as slug pellets. The results showed that copper barriers were effective in reducing slug damage to cereal crops.