Controlling Slugs with Ammonia – Which Methods Work?

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Robert Pavlis

Household ammonia is reported to be great for controlling slugs. Some people spray the slugs directly and apparently it kills them. Others spray plants so slugs stop eating them. Spraying soil is also a common method of controlling slugs and snails.

Do these methods work?

Ammonia is a strong cleaning agent and it surprises me that spraying it on plants will not harm them, but maybe the dilution used is low enough to prevent damage. If that is true, what is the ‘safe’ dilution ratio?

Controlling Slugs with Ammonia - Which Methods Work?
Controlling Slugs with Ammonia – Which Methods Work?

What is Household Ammonia?

Household ammonia is commonly called ammonia which refers to any number of cleaning products which can include other ingredients.

True ammonia is a gas at room temperature with the formula NH3. It is also called anhydrous ammonia. Nobody uses this in the home or garden.

When ammonia is dissolved in water it forms ammonium hydroxide which is the same as household ammonia and it contains 5-10% ammonia. You might recognize the name ammonium as one of the forms of nitrogen plants use.

Compost Science for Gardeners by Robert Pavlis

I tried to buy some of this a few months ago and couldn’t find it. The only products I found had other ingredients added, like coloring agents, smell blockers, soap. I guess companies are trying to make a better cleaning product that does not smell so badly.

What do these extra ingredients do to plants and slugs? I have no idea. Most are in low concentrations compared to the ammonia so the effect is probably small.

Properties of Ammonia

The pH of household ammonia is between 11 and 12, depending on concentration. This is a very alkaline solution.

The other property that is important for this discussion is the stability of the product. Remember that household ammonia is water and ammonia. The latter is a gas at room temperature and as such it evaporates quickly. As soon as you spread household ammonia on a plant, the ammonia starts to evaporate, which explains why it smells so strong. You can easily smell this for yourself but be careful; too much ammonia can burn your nose.

I also prepared a video where you can see my slug actors reacting in real time to the effects of spraying soil, leaves and directly spraying the slugs.

YouTube video

If this video does not play try this link; https://youtu.be/79FITnxcViU

Diluted Solutions of Household Ammonia

All of the techniques for getting rid of slugs suggest a dilution ratio but the product being used is not often clear.

For example: “use diluted ammonia (5 to 10% solution) “, which comes from a government site.

If we take a literal interpretation, you should use household ammonia right out of the bottle since its already a 5-10% solution of ammonia. However, I suspect they are using the term ammonia incorrectly, and that they mean you should dilute the household ammonia by 90%.

Many of the suggested mixtures on the internet suffer from this problem.

Drop Slugs in Ammonia

One way to deal with slugs is to physically collect them and drop them into some household ammonia. A 10% solution will do the job.

I have no doubt this works. Apparently soapy water also works.

Spray Slugs with Ammonia

Picking slugs is not everyone’s cup of tea, so some prefer to just spray them right on the plant, or as they travel along the ground. Lots of reliable online sources and even some YouTube videos confirm that this works, which should be no surprise given the high pH of household ammonia.

But what concentration should you use?

I checked several government sites and got a range of 5% to 80% household ammonia. If 5% works, why would anyone recommend 80%?

A concern with this method is the effect on plants. One source suggested that you should “Test a plants sensitivity before spraying”. Are you going to test every plant in the garden? I could not find any information about plant sensitivity to household ammonia.

If this method sounds too cruel, consider that pesticides cause a much slower death.

Spray the Plant or Soil

Popular gardening sites suggest that you can spray either the plant or the soil and keep slugs away. An added benefit of this technique is that the ammonia provides a nitrogen feed for the plants.

The common dilution for this technique is a 10% solution (1 part household ammonia to 9 parts water).

Virtually all of the government websites (sites with a edu extension) say that if you use ammonia to control slugs it needs to be applied directly to the slug. They DO NOT promote the idea that spraying plants or soil works.

The problem with this technique is that ammonia evaporates quickly.

I tried a quick test. I spread some household ammonia on a hosta leaf. The smell was quite strong from the evaporating ammonia but it only lasted for about 3 minutes. Admittedly, my nose is not the most sensitive analytical instrument, but even the water evaporated in a few minutes. Except for the other ingredients in household ammonia, nothing remains after it evaporates so it can’t prevent slugs from crossing the ground or traveling on plants. It is highly unlikely that either of these techniques work.

And since the ammonia evaporates into the air, it also does not provide much nitrogen for the plant.

One source suggested that the soil should be ‘drenched’ in early spring. I guess if you apply enough ammonia solution to the soil you will kill newly hatched slugs and maybe even eggs when the ammonia contacts them. This would take a lot of ammonia for even a small garden.

Getting Rid of Slugs and Snails

I have written extensively about this topic. Most DIY techniques do not work, or have a limited effect. Slug bait works best and is relatively safe.

 

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Robert Pavlis

I have been gardening my whole life and have a science background. 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!

20 thoughts on “Controlling Slugs with Ammonia – Which Methods Work?”

  1. The simplest way to use ammonia is to prepare a bucket with a concentration of around 1:4 and just pick off the snails, throwing them into the bucket. Death is instantaneous.

    Reply
  2. The suggestion I’ve read is that diluted ammonia, sprayed under leaf cover, kills slug EGGS. I’m hoping you’ll analyze it for us! My concern (besides possibly completely wasting my time) is: if it kills slug eggs, might also harm slug predators (or their eggs). Any comments would be helpful, thanks!

    Reply
    • Both slugs and snails hide their eggs. You would have to saturate your whole garden soil to get to them.

      Reply
    • A neighbor an I did have slugs on our gardens/yards, and nearly every evening, throughout the summer, we sprayed the yard with a solution of ammonia. 1 ammonia to 9 parts water. We made an effort to spray the soil and lawn of course. We didn’t find the solution to harm any plants that we grew. Of course, that doesn’t mean that there is some plant that will react. The result, is that we are no longer battling slugs. The thing is, you have to be consistent about spraying. Certain plants, we did test. Especially the ones that slugs love. You can’t say it doesn’t work if you are not dedicated.

      Reply
      • I’m not sure what you mean by “limited effect” but for a start most slugs natural predators are at risk if/when eating poisoned slugs. Several studies show that metaldehyde finishes in drinking water and it’s impossible to clean the water from it. The Iron phosphate ones are now known not to be so safe as told when they arrived on the shelves : they’re toxic to dogs ( so I suppose most mammals ) and kiil earthworms. As an amateur gardener, I know my soil is good by the amount of worms. One thing I’ve learnt ( I live in Ireland, heaven for slugs ! ) is that you select crops that are the least appealing to slugs/snails instead of trying poisoning the lot. Using baits in the garden, like pesticides, herbicides etc with the informations we’ve got now about their very damaging impact goes against common sense, and certainly against my gardening ethics.

        Reply
        • This article is not about metaldehyde and was not mentioned until YOU interjected it into the conversation. If you want to debate someone, stick to the topic instead of changing it to fit your argument. Who knows, if you spent the time, you may be able to do some research and, actually, make an argument against ammonia; but, maybe not.

          Metaldehyde is, actually, an organic compound with, very limited effect on Wildlife and IS, usually, applied in “pellets” of wheat, which IS a “bait”. Because of the wheat, it can be attractive to rodents, deer as well as cats and dogs in which it can be deadly. Ammonia occurs naturally as plant material decays. Does this make it any safer than other “natural occurring chemicals” such as when vegetable oil is made and that process releases ricin (one of the most poisonous, naturally occurring, substances in the world).

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    • This is not a “bait”. Baits attract a “thing” (animal, person, bug, fish, etc) because it smells, looks, etc, attractive. Your perfume is a “bait”.

      Again, this is NOT a “bait”. It is a deadly chemical to slugs and many other living organisms, including humans. But, just as using your perfume in the wrong way (drinking it, spraying it on bugs, slugs, etc) would kill, so will ammonia, dishwashing detergent, beer, and even water, if used wrong or in excess.

      Why do we use it? For the same reasons we, as humans, use perfume, saps, shampoos, body wash, chemicals to process our food supply (including LOTS of ammonia, toilet bowl cleaners, car wash chemicals, sun block and the lotions, hair products and makeup that are all lade with chemicals that, if misused, cam be deadly to us, others, and other living things. Yes, even slugs.

      Is any of this, socially responsible”? Well, you did not ask THAT question. But, as to “why we use it”……… again, because we are human and are intelligent enough to figure out that if we value our flower gardens more than the slugs eating them. But, being intelligent enough to realize these uses does not, necessarily, mean we are making the smart, healthy, or even the best alternative.

      But, as for MY choices, for MY hosta, I choose to prevent them from being ravaged by slugs yearly by using this method in as smart of a manner possible.

      Reply
        • What you SHOULD have typed is that it HAS not worked, yet, for YOU. This is an indication that you are not using it correctly. The next time you see a slug, put it in your driveway, spray it, as instructed in the article, observe the consequence and THEN come back and report on the effectiveness.

          Reply
          • Too bad you did not read the article. I clearly said that covering a slug with ammonia would kill it. I even demonstrated it in my video.

            What does not work is spraying the ground.

  3. Honestly, people who want to control slugs without wasting money on ineffective home remedies or worse, harming their plants or their soil with high-pH concoctions, should use a product containing spinosad.

    I do wish you’d mention it. Spinosad is a naturally occurring bacterium that can be toxic to certain garden pests. Spinosad is found present in fermentation juices of the soil bacterium Saccharopolyspora spinosa. Spinosad has been certified for use in organic agriculture since 2003 by the USDA National Organic Program (NOP) and is OMRI listed.

    I’ve used this on plants that get absolutely destroyed by slugs, like hostas and dahlias and strawberries … and it works perfectly and quickly. I’ve tried many of the “home remedies” and they don’t work well (if at all) and have to be constantly reapplied. A shake of spinosad granules is effective for weeks. And it is approved for organic use!

    Reply

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