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Ammonia Spray for Slugs on Hostas: Does the "Ed Lawrence Solution" Work?

Published 2026-11-12

Canadian gardeners have passed around a slug remedy for at least twenty years: spray diluted household ammonia on hostas or on the soil around them in early spring. It is often credited to Ed Lawrence, the gardening expert on CBC Radio’s phone-in shows. We looked for what extension services, master gardeners and research actually say. The short version: ammonia kills slugs it touches directly, but the evidence that a spring soil spray kills slug eggs is thin.

Quick answer

  • Direct spray on a slug: works. Colorado State University Extension calls ammonia sprays “excellent contact molluscicides” that “must be applied directly to exposed slugs” (CSU Extension).
  • Spraying leaves or soil to keep slugs away: unlikely to work. Ammonia evaporates within minutes and leaves nothing behind that slugs would avoid (Garden Myths).
  • Spring soil spray to kill eggs: the idea is plausible but unproven. The only test we found dipped eggs in a solution in a lab. Nobody we found has measured it in a garden.
  • Dilution: published recipes range from about 1 part household ammonia to 10 parts water up to roughly half and half. Test on a few leaves first.
  • Safety: never mix ammonia with bleach. In Ontario, a cosmetic pesticide ban may cover this home remedy outdoors (see below).

Where the “Ed Lawrence solution” comes from

We could not find the recipe in anything Ed Lawrence wrote or in a CBC archive. What exists is secondhand. On January 11, 2005, a poster on the ICanGarden forum wrote that she “heard on CBC radio’s gardening show with Ed Lawrence” that a water and ammonia solution “around your plants in the early spring will really cut down on slugs as it kills the eggs that overwinter in the soil” (ICanGarden forum, archived). The ratio in that post is garbled (“1-40%”). Later posts in the same thread used 1 part ammonia to 9 or 10 parts water, and one poster credits that ratio to Ken Beattie.

A reader question on the Toronto Master Gardeners site also says “Ed Lawrence gave such a thing using ammonia and water” and asks when to apply it against eggs (Toronto Master Gardeners, archived May 2024). So the claim people repeat is specific: a spring spray that kills overwintering eggs in the soil. That is the part we checked hardest.

What household ammonia is

Household ammonia is ammonia gas dissolved in water. It contains about 5–10% ammonia and has a pH of 11–12 (Garden Myths). Some products add soap or scent. Check that yours is plain, and read the label, because strength varies by brand.

Does it kill slugs? On contact, yes

Colorado State University Extension, in its fact sheet on slugs, says: “Ammonia sprays make excellent contact molluscicides, but must be applied directly to exposed slugs. Household ammonia, diluted to a 5- to 10-percent concentration, is effective for this purpose” (CSU Extension). Robert Pavlis of Garden Myths notes that government sources almost all say the same thing: the spray has to hit the slug (Garden Myths).

In practice this means going out after dark, when slugs feed, and spraying each one you find. It is hand-picking with a spray bottle instead of fingers.

Does spraying leaves or soil keep slugs away? Unlikely

Pavlis put household ammonia on a hosta leaf. The smell “only lasted for about 3 minutes”, and “nothing remains after it evaporates so it can’t prevent slugs from crossing the ground or traveling on plants.” He calls it “highly unlikely” that spraying plants or soil works as a barrier (Garden Myths). We found no study that tested a residual effect.

Does a spring soil spray kill slug eggs? Not shown

This is the claim credited to Ed Lawrence, and it has two parts.

Where the eggs are. In a lab study of the gray garden slug (Deroceras reticulatum), slugs laid clusters of 21 to 43 eggs “in or a top the soil”. The eggs took 23 to 27 days to hatch (Annals of Agricultural Science, Moshtohor, 2015). The Toronto Master Gardeners add that eggs often sit on the soil surface under debris or leaves (Toronto Master Gardeners, archived). So a soil spray could, in principle, reach some of them.

Whether ammonia kills them. The same study dipped eggs in four solutions for 10 to 50 seconds. Ammonium hydroxide, the chemical in household ammonia, “exhibited the highest effect against eggs by preventing its hatching at the concentration 1.5% for dipping period 20 seconds.” Onion juice and potassium chloride also stopped hatching at slightly different strengths and times (Annals of Agricultural Science, Moshtohor, 2015).

That is the strongest evidence we found, and it has clear limits:

  • The eggs were fully dipped for 20 seconds. Eggs under leaf litter or in soil crevices may never get that much contact.
  • It was a lab test, not a garden.
  • The abstract gives a percentage but does not say how it relates to a bottle of household ammonia, so you cannot turn it into a garden recipe.
  • Pavlis points out that drenching enough soil to reach the eggs “would take a lot of ammonia for even a small garden” (Garden Myths).

Larry Hodgson of the Laidback Gardener writes that the treatment “seems most effective on young slugs when they hatch in the spring” (Laidback Gardener). That matches the contact effect: newly hatched slugs are small and exposed. It does not show that the spray kills eggs.

Dilutions in circulation

SourceRecipe
Colorado State University ExtensionHousehold ammonia “diluted to a 5- to 10-percent concentration” (CSU Extension)
Garden Myths (Robert Pavlis)Common dilution is 1 part household ammonia to 9 parts water. He reads the “5 to 10% solution” wording on government sites the same way, and says the range he found on government sites ran from 5% to 80% household ammonia (Garden Myths)
Haliburton County Master Gardeners1 part ammonia to 10 parts water, sprayed on leaves with a hand sprayer; an alternative mix of 1½ cups ammonia, 1 tbsp Murphy’s Oil Soap and 1½ cups water (Haliburton County Master Gardeners)
Laidback Gardener (Larry Hodgson)1 part household ammonia to 6 parts water, weekly as needed (Laidback Gardener)

The second Haliburton mix is close to half ammonia, far stronger than the others. None of these sources gives a tested limit for hosta leaves.

Will it burn hosta leaves?

It can. Hodgson notes that ammonia is “very alkaline and, at full strength, may burn the foliage of delicate plants” (Laidback Gardener). Pavlis says he could find no information on how sensitive different plants are (Garden Myths). If you try it, use the weakest common mix (1 part to 10), spray a few leaves, and wait several days before spraying the whole plant.

You may read that the spray also feeds hostas with nitrogen. Hodgson says so; Pavlis says most of the ammonia evaporates before the plant can use it. Either way, do not count on it as fertilizer.

Safety

  • Never mix ammonia with bleach, and do not use a sprayer that held bleach. The mixture gives off toxic chloramine gases (Washington State Department of Health).
  • Ammonia solutions “can cause skin or eye burns”. Wear protective clothing and eye protection (Virginia Department of Health).
  • Label the sprayer and keep it away from children and pets.

A note for Ontario gardeners

The Toronto Master Gardeners say they “do not recommend chemical control for any pests” and that “the Ontario ban on use of pesticides for cosmetic purposes included a ban on home remedies, like use of soap and diluted ammonia outdoors” (Toronto Master Gardeners, archived). We have not checked the current wording of the Ontario rules. If you garden in Ontario, check them before you spray. The same applies anywhere local rules restrict home-made pesticides.

What works better against slugs on hostas

The Toronto Master Gardeners’ own advice for slug eggs is to clean up the yard and remove organic debris, wood and anything else slugs can hide under. Then hand-pick slugs in the early evening, about two hours after sunset, and trap them under upturned citrus rinds or flower pots (Toronto Master Gardeners, archived). For a summary of what the evidence says about barriers, traps, nematodes and baits, see the slug section in our hosta care guide.

If you do use an ammonia spray, use it the way the extension sources describe: at night, directly on the slugs you find. That is the one use the evidence supports.

What we did not check

We have not tested ammonia sprays on slugs or hostas ourselves. We did not find a primary recording or text from Ed Lawrence, so what he said rests on listeners’ reports. We read the abstract of the 2015 egg study, not the full paper, so we do not know exactly how its percentages were measured. Sources were checked on November 12, 2026.

Sources