Can you spray this on the leaves or do you spray it around the plant in the dirt?

I would spray it on older plant leaves but not seedlings.
Hope that helps

Thank you for the tip!

Something else I learned here on ATP as a deterrent (won't kill slugs already present) is to put coffee grounds all around the base of the plants. It worked really well for the strawberry plants I did that do. (The strawberry plants without the coffee treatment were always pocked with slug-bite holes.)

Wow, ammonia diluted only 1:2! Pretty strong, like 2.5% to 5% ammonia.

I think there are some plants whose leaves might ask you to rinse that off afterwards. As you say, "not seedlings".

Here is everything I've read about that, but I haven't yet started tested them.
These people suggested that spraying slugs directly with much weaker solutions (0.25% to 1% Ammonia and no detergent) would kill slugs, dissolve eggs, and make SOME plant leaves unhappy.

I see that store-bought ammonia has a range of strength, so they may be using cheap ammonia and maybe you have The Good Stuff.

But yours sounds like it works very well, and they talked about their ongoing struggle, if I recall.

So I'm thinking that I should experiment next spring. Spray a row with 3 different strengths, and see which get eaten.

"Household ammonia ranges in concentration by weight from 5 to 10% ammonia."

So 1:2 dilution is 2.5% to 5% NH3.
1:5 dilution is 0.5% to 1%
1:10 dilution is 0.25% to 0.5%.


The source links are now broken, but:

"Ammonia water: 1 part ammonia to 9 parts water. (Can spray the plant, but then rinse).
If you've got Lilies or Asters be extra-vigilant. I use a spray bottle and do ground/plant where I feel there may be little buggers hiding, ..."

"someone else said "20%" or 1 part ammonia plus 4 parts water (maybe not directly on plants)

I've used ammonia diluted 1:10 with good results. I have also diluted it more than that and it seems to work too. I feel strongly that 1:1 or 1:2 is far too strong and one will risk damaging plants. Besides, the ammonia will go much farther diluted more and cost a lot less. I've got over 200 hostas and even at 1:10 I go through 5 or 6, 2 litre bottles of ammonia.

May be sage advice. Every one should try and see how it works for them. I might try a lower solution myself.