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How to Get Rid of Slugs with Diatomaceous Earth

Slugs, slugs, slugs – everybody wants to get rid of the slugs and there are all kinds of methods that are reported to work. I have already reviewed several of these including:

What about diatomaceous earth? Apparently, the sharp edges in diatomaceous earth cut the bellies of slugs, and they bleed out and die. Diatomaceous earth is used effectively for controlling insects, so maybe it works on slugs. Time for an experiment.

Diatomaceous Earth - diatoms

Diatomaceous Earth – diatoms

What is Diatomaceous Earth?

Diatomaceous earth, also known as DE, diatomite or kieselgur/kieselguhr, is a soft silica-based rock with particle sizes in the range of 10 to 200 micrometers, or a fraction of a millimeter. The rock consists of fossilized diatoms which are a form of hard algae.

DE is available in two different grades; a food grade and a pool filter grade. For horticultural purposes you should always use the food grade or a product marked for pests. The pool grade is processed differently and will not work.

In horticulture, diatomaceous earth is used as a pesticide. When it is applied to insects, it removes their waxy protective coating, and may cause scratches in their exoskeleton, leading to dehydration and death. If it can kill insects, it might also work on slugs? A lot of information on the internet certainly says it works.

It is claimed that the sharp edges of the diatoms cut the foot (ie the bottom) of the slug, and the slug either bleeds to death or dehydrates due to a loss of moisture.

Warning: slugs and snails were hurt in this experiment and were eventually killed!

Slug Control – Experiment Setup

The experiment is designed to test two things:

a) will slugs (and snails) cross a line of diatomaceous earth? If it were placed around a plant, would it stop the slug from getting to the plant.

b) if a slug crawled across the diatomaceous earth, would it get cut so bad that it dies?

Testing (a) above is fairly simple. Make a ring of diatomaceous earth, and place a slug in the center of the ring. See what happens. If they won’t cross the DE, they will remain inside the circle.

Testing for (b) is a bit more difficult. What do cuts on a slug look like? Do they bleed? I am no slug expert, and don’t have a good stereoscope to check for cuts. I decided I would take a different approach. Let the slug crawl over some DE, and then see if it dies. I don’t really care if they get cuts, or how many cuts they get. As a gardener all I care about is that they die from the exposure.

Collected slugs and snails were kept for a few days in a plastic container with water and some decomposing fruits and vegetables for food. They seemed quite content in their surroundings and were eating well.

Do Slugs Cross Diatomaceous Earth?

The pictures below show some tests to see if snails cross the DE. The experiment was also carried out with slugs and no difference was found between slugs and snails.

When they are placed in the circle they start to crawl and soon reach the DE. Their upper and lower tentacles reach out to sense their surroundings. The upper ones have eyes but they only see light and dark. The lower ones are sensitive to smells. Both are also sensitive to touch.

As the tentacles came close to the diatomaceous earth, they immediately withdrew. Since both types of tentacles withdrew, it seems logical to conclude that they did not like the feel of the DE. Maybe they can feel the sharpness?

In any event, the snails never crossed the DE. When they got close, they turned around and tried to escape by a different route. They did however get some DE on themselves while trying to cross.

Slugs and Diatomaceous Earth 4

Snails trying to cross a ring of diatomaceous earth

The slugs were returned to their plastic home for 48 hours to see what effect the DE had on them. As you can see in the picture below, there were no short term effects.

Slugs and Diatomaceous Earth 6

Same snails, 48 hours later, completely unaffected by the diatomaceous earth

The test slugs and snails in this trial would not voluntarily crawl over the DE. Provided it is dry and the band of DE is wide enough and thick enough, the DE will prevent the slug from reaching the plant most of the time. In one trial, a snail crawled over another snail, thereby completely missing the DE – he got away.

Does Wet Diatomaceous Earth Work?

Both the packaging and information on the net says that DE is only effective when dry. I repeated the above experiment after dropping some water on the DE. They had no problem walking on wet DE.

Snails on wet diatomaceous earth

Snails had no problem crossing wet diatomaceous earth

Does Diatomaceous Earth Kill Slugs and Snails?

Since the slugs did not cross the DE, I had to find a different way to expose them to diatomaceous earth. I simply picked one up, and dropped him or her (they are hermaphrodites) into a pile of DE. It was forced to crawl on the DE and it got quite covered in the stuff.

It clearly did not like this experiment – did I hear small sequels as the DE cut its belly? I’m not sure.  It kept retracting its various body parts, trying to get away from the white powder. Eventually it did get off the pile.

Poor thing! I just picked it up and put it right back on the pile. This time it took longer to get off the pile. The snail did seem to be in some distress or maybe it was just unhappy with its situation. By the time it get free of the DE for the second time, it retracted into it’s shell and just laid there. I figured it was a goner.

Slugs and Diatomaceous Earth 1

Snail, unwillingly playing in diatomaceous earth

The slug was returned to its plastic home for 48 hours. I expected it to die from its lacerations, but as you can see in the picture below, it was fine. You can still see some of the diatomaceous earth on his shell.

Slugs and Diatomaceous Earth 5

Snail 48 hours after exposure to diatomaceous earth – alive and doing well.

I repeated the experiment with a slug to see if there was a difference in survival rate.

Slugs and diatomaceous earth

Slug, unwillingly playing in diatomaceous earth

Slugs and diatomaceous earth survival

Slug several days later doing just fine. The shed DE is still visible.

Clearly diatomaceous earth does not kill the type of slugs or snails being tested here. Maybe they will die in a couple of weeks, or months from infection or chemical exposure, but as gardeners, if they don’t die fairly quickly, then DE is of no use to us for killing slugs. Diatomaceous earth did not kill slugs in this test.

Diatomaceous Earth Does NOT Cut Slugs

Ever since I read that the sharp edges of DE cut the bellies of slugs, I had my doubts. Slugs are used to crawling all over things. In my post Eggshells Control Slugs – Do They Really Work?,  you can see a video of them crawling over knives and raiser blades. Why would a white powder hurt them?

To understand this better it is important to understand slug slime. Reference 1 and 2 can provide some details, but in short, the slime protects the foot of the slug from cuts.

While watching the slugs, I noticed that where the slug touched the DE, the DE turned from white to gray. After a few minutes it turned back to white. The gray color is an indication that water/slime had been transferred to the DE. The slime from the slug is making the DE wet and ineffective.

I don’t believe that diatomaceous earth cuts slugs – it is another myth.

Does Diatomaceous Earth Deter Slugs?

I believe it does to a certain extent. If you surround your plant with a line of DE that is as wide as the biggest slug foot in your garden, it will prevent them from getting to your plant. But….. there is always a but.

Rain will wash the DE away and wind will blow it away, so it needs to be applied regularly. When wet, it stops working and slugs like wet places. So don’t apply it after watering or after a rain – you need to let the soil dry out first.

It is not cheap. I don’t think that it is an economical way to keep slugs away from a number of plants. Saving one or two special plants – Ok, but if you try to protect your collection of 40 hostas, you better have lots of cash.

There is one fundamental problem with ringing your plants with DE to keep slugs out. You have to make sure the slugs are not inside the circle, before you put the DE on the soil. If they are, you are caging them in and forcing them to eat the plant you are trying to protect.

Bottom line – DE works to deter slugs, but I question if it is a practical solution for anything more than a couple of plants. In any event it does not kill the slugs.

Slug Sex

What has this got to do with DE you ask. Nothing. But the following video is so cool you have to watch it.

Apparently this video has been blocked in the UK, which is odd since the BBS has share enabled on this video, which means they authorize people to share the link. If you can run the above, here is the link “https://youtu.be/wG9qpZ89qzc”.

References:

1) What is The Slime That Comes From Snails and Slugs? : http://animals.mom.me/slime-comes-snails-slugs-5801.html

2) Slugs – Interesting Facts, Mucus Slime, and Pest Control: http://hubpages.com/hub/Slugs-and-Slug-Slime

3) Photo Source: pali_nalu

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

20 Responses to 'How to Get Rid of Slugs with Diatomaceous Earth'

  1. Jennifer Schuchman says:

    You answered my question on DE and I so appreciate your generosity in taking the time to share your knowledge.

  2. Robert that looked like RAW DE. How about if you used a calcined or fired DE? I suspect the same results but just asking.

  3. Paula Beattie says:

    What about copper to repel slugs? DE didn’t work in my garden either, but ammonia did. Unfortunately it is at night when they come out, so I had to go out to my hostas with a flashlight and look under every leaf. After a week or so, there was a definite improvement – this is now my ‘go to’ method.

  4. Trishi says:

    OK, you have debunked DE, egg shells, coffee grounds and all except beer/yeast. What DOES work ??

  5. Anne says:

    Thank you for experimenting with diatomaceous earth which I wondered about using.

    I’ve been pleased with how easily diluted ammonia (the kind with no detergent added!) kills slugs. After using it in 2014 every morning spritzing it around on any slugs seen on my annuals and perennial plants, not just hostas, it was so successful that we hardly had any slug damage. And this year, hardly any slugs period. I don’t know if there was a change in the weather that caused this or last years ammonia blitz attack that caused the decrease. I left the mulch on the ground as usual so they had plenty of places to hide and lay eggs if they were alive.

    • I have no doubt ammonia will kill the slugs. If you kill a lot, there will be fewer babies around for next year.

      It is also possible the that climatic conditions changed and caused fewer slugs the following year. Or it could be a combination of the two.

  6. Don says:

    My July 26 comment indicated that I had not noted any slugs at that time, and that when I did, I was going to try ammonia on them. They have now appeared, in smaller numbers than prior years. This may be due to different weather conditions, or possibly actions taken in prior years – there’s no way of telling. I did clear the hosta leaves, cut back other plants and cleared debris last fall – which may have resulted in a less hospitable environment for eggs? I had also tried spraying a neem oil solution in the affected area during last year’s slug season – some have claimed it may interfere with the reproductive process. In any case slugs did appear this year, and I sprayed them with a 20% solution of ammonia. Contrary to my experience with DE, in which the slugs appeared to have been immobilized, but later recovered – the ammonia solution killed the slugs. I placed some in a plastic container and sprayed them to satisfy myself that they didn’t recover in a few hours – they did not. Also those that remained on the hosta leaves when sprayed, remained there and were definitely not going to recover. I have no doubt that the mixture is lethal for the slugs that we have been dealing with. As for damage to the plants, I noted no damage to the hostas or surrounding plants – with one exception. One small area of thyme that received a large amount of the mixture was burnt beyond recovery. My wife believes some of the hostas might have become discolored. As some of the leaves had been damaged by hail, it is possible that the mixture browned the damaged edges. However, with these exceptions there appeared to be no plant damage. When the slugs did appear, I sprayed them directly, and misted the entire plant, also used the stream setting to get the solution down the stems to the base of the hosta. I did this in the early evening, by flashlight, for a week. I also checked in early morning, and sprayed any area that a slug was spotted. The number of slugs that I sighted declined, until there were several successive evenings and mornings that none were evident. I’m sure there are still a number around, but the population appears to be substantially reduced, as well as the damage to hostas and surrounding ground cover. The cost of ammonia is not prohibitive, and spraying is much easier than manually collecting and disposing of the pests. I used a small [48oz] Chapin spray bottle, which was ideal for the job. I would be interested in reading comments of others on control of slugs, including any experience on using ammonia [or other methods] to eradicate the eggs.

    • Ammonia is basically a nitrogen fertilizer which is alkaline. It certainly kills slugs on contact. But here is the potential problem. Too much nitrogen fertilizer on plants or the soil can damage plants. We all know that from burnt grass after fertilizing. so the trick is to use enough to kill the slugs and not damage plants.

      You could try diluting the ammonia until you reach a point where it no longer kills the slugs. Then use it just a bit more concentrated.

  7. Don says:

    I have tried DE on slugs and can confirm your conclusion. Initially, I thought it might be the answer. Whether through “cuts” or by some other process, it did seem to dehydrate the slugs when it was applied to them on the hosta leaves, they would either appear dead or fall off the leaf. When I returned the supposed dead ones were not there, only the discolored DE where they had appeared to be on their death bed. I followed up on this, picking slugs and placing them in an open plastic container filled with DE. They certainly did not enjoy the DE, and it did dehydrate them, but all appeared to survive and start on their escape. I do believe DE could be used as a barrier, it may not be excessively costly, but time consuming, as rain or watering would eliminate the barrier – and the other problem you mentioned, were you keeping them out or keeping them in the area you wanted to protect.
    With DE off the list, this year I plan to try an ammonia solution, sprayed directly on the slugs when they begin to forage. So far this year we have not seen signs of slugs. As a number of others in this area have never encountered slugs, I’m hoping I can get rid of them and not be bothered in the future This past fall, I cut back the hosta leaves and cleared these and other debris from the infected area. This had not been done previously, as my wife had thought the debris provided some protection to the plants over the winter. I’m hoping the harsh winter may have cut down the slug population, but suspect I might be back after the season reporting on the latest failure in dealing with the pests.
    An article that may be of interest is the use of neem oil, in pest control. I’ve heard it suggested as a solution for slugs, and also on other pests. As I understand it is a systemic that interferes with the reproductive process, it may be difficult to research – but is also intriguing if there is any truth to the claim that it could inhibit reproduction of leaf eating pests.

    • Looks like your experience mirrors my tests exactly.

      I did try Neem years ago when I grew over 1,000 orchids in the house. Compared it to baby oil for mealy bugs and scale. I found baby oil worked just as good and smelled a lot better. I have added Neem to my list of things to talk about – thanks.

  8. rogerbrook says:

    ps your video was blocked in England on copyright grounds!

  9. rogerbrook says:

    What a great series of little tests Robert!
    I am not sure this stuff is used over here but I remember when I visited gardens on your continent in Seattle fifteen years ago a gardener was using it – or something very like it.

  10. This was a hard read, not because of your warning 😉 but because I don’t like slimy things. It is sure now that you will never get any endorsements from the ‘garden products industry’!
    I saw snails crawling happily over sharp rock on the mountain too and I was wondering about the diatomaceous earth claims.

  11. Jodi DeLong says:

    I like your style, Robert. You explode garden myths nicely, but with humour and explanations. I ran a (not scientific) experiment earlier this summer to see if DE would deter scarlet lily beetles or their larvae, and it seemed to be deterring them in one location–but then I got busy with editorial duties and forgot to track it. Next year, perhaps a controlled experiment to see if it does have some merit!

    • I have not finished my research into DE + insects/beetles, but there seems to be credible evidence that DE does in fact kill them. I doubt it will have much of effect on the lily beetle grubs.

      I did try DE on a wasp nest which is located in my dock – and it certainly did not get rid of them. It might have killed a few?

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