1:20 is half the strength of 1:10, so nothing should have burned, that would be 1 part ammonia to 20 parts water or 1 part ammonia to 10 parts of water. Now, I would think that something like 1:5 or lower could burn the hostas.
Opps, sorry... 25 per cent was mentioned, I am surprised that did not burn them but maybe cooler weather you could get by with that, I would be concerned in hot weather, but maybe not. I try to keep my mixture around 1:10 so I have no experience with a 1:4 mixture.

This is a great article. (link) this lady uses 1:5, that's one part ammonia to 5 parts water. And she does say you can use it stronger. (You have to do your own experiments like I did last year. ) The stronger solution was mainly for my daylilies because the flowers would be tore up each morning, by the time I got out there with a camera. LOL.

When I read an article in Fine Gardening a lady who commented said she used it full strength on everything. After that I was not afraid of it anymore. I have used it on everything, I have acidic soil and slugs love it here. I have not experimented on dahlia shoots, I am waiting for mine to sprout and I have a cheapo in a pot as the sacrificial plant for testing. The others in the yard are more expensive, wish me luck!

I was shocked that this woman said that you can reduce the slug population by changing the PH in your soil. She said after you spray the whole yard with ammonia you should do a surface dusting with lime and she tells you how. I might consider this!

Also don't forget ammonia is a foliage spray. It breaks down quickly into nitrogen and is absorbed by the plant. Good stuff!

http://www.hillgardens.com/slu...

That is why I don't mind spraying the ammonia several times a week, even if I don't see any slugs, I feel I am killing the eggs, and if not that at least I am giving the plants a boost of nitrogen which seems to be low in some spots in my garden beds where I have added so much organic matter and the earth worms have not taken over yet. Never would have dreamed of using it straight, but I do prefer the green tinted ammonia, it has done no harm so far and I can tell at a glace which spray bottle to pick up.

I do not use it full strength either. It would just be a waste if 20% does the job! I am going to put some into my gallon hose sprayer next weekend when I am off and spray everything real good even the soil and then do lime the next morning and hose it down that evening. I will let you know how it goes, but I still keep the bottle by the door in garage in case I see one crawling around. Remember...''never let a slug get away!" LOL.

well upon further investigation it seems my hotas are being eaten by inch worms. I still haven't found any worms. But I have found several on nearby trees and my coleus. So I am thinking it could be that. I do know they will eat a very large amount in a short time. They are so camouflaged that they are hard to see, and tiny too. oooo I hate them. The problem is, it has been raining here almost every day, most stuff you have to respray after each application.

I have never burned my hostas with the ammonia, but those of you who were on DG might remember Sandy - Sanannie. She's got a fab. garden and she burned some of hers using a stronger solution of ammonia. Memory does not serve me as to how strong. But bottom line, 1:10 will do the job. Likely even 1:20 will do the job. The stronger the solution, the more ammonia you will need to buy; so why use a stronger solution than necessary?