Urine?

Something dead in the bushes?

There is no cat, so it isn't urine. Nothing dead; it's not a dead animal smell. No fertilizers or chemicals have ever been spread here. No visible fungi. I am so curious.

Not me, I haven't been sneaking in and spraying Ammonia. Seriously though. Compost Ammonia Odor Compost ammonia odor is frequently observed in piles of organic matter which have not been turned. Turning of compost introduces more oxygen to the matter, which in turn enhances the work of the microbes and bacteria that break down the matter. Additionally, compost that is too rich in nitrogen requires air circulation and the introduction of a balancing carbon, such as dry leaves.

Read more at Gardening Know How: Treating Common Ammonia Odors In The Garden https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/ammonia-odors-in-garden.htm

Ammonia and water mixture kills slugs. Perhaps that is why I can’t see even one tiny slug hole on your hostas there. I have to make the mixture and douse all my plants, spring and fall to get my hostas looking that perfect. Can’t imagine what it is, but if it’s killing slugs, I say yay!

debra

i presume you would know if you had a septic tank

Most importantly if you have just had mulch delivered or installed it mat be sour and kill your plants. You should check your ph if you suspect this.

"Sour mulch" has nothing to do with pH . And it doesn't kill your plants!! A sour mulch is one that is just anaerobic, much like the compost described earlier. Any bagged soil product that remains enclosed in plastic and left outside exposed to the weather can become anaerobic and develop a strong ammonia aroma. But it typically dissipates rapidly once spread out, exposed to the air and allowed to dry a bit.

https://gardeningandgardens.blogspot.com/2014/07/sour-mulch-and-its-devastating-effects.html It can be devastating.

Mulch has to be turned to prevent this problem. There are many references to the devastation it can cause. If it is the mulch then the only thing to do at this point would be to do the turning that the supplier should have done. I would rake up the mulch and try to dissipate the gases. Smelling ammonia from mulch is not good at all. Spreading it out is the answer, if left it can and has caused big trouble. The mulch smells ammonia so it should be worked to get rid of the ammonia. - Jon

The above is known as wood alcohol syndrome and is generally only associate with wood chips that have been piled too high and left too long. It seldom ever occurs with any bagged mulch product. The ammonia smell is more typically related to anaerobic conditions.....which are very easily cured.

Bottled household ammonia is diluted and diluting it further and using it to kill slugs is a weak fertilizer as well as being beneficial killing the slugs. Wood chips or mulch made from ground wood are the same material. Good suppliers will "turn" their mulch, chipped or ground preventing a build up of ammonia that can be harmful or even fatal to plants. Ammonia produced in this way is straight ammonia. If you can smell ammonia with no obvious cause and it is coming from a planting bed it is a good idea to rake out the mulch to get some oxygen (air) into the mulch which will cure the problem. Myself I would hose it down to wash the ammonia away as well. Leaving it alone can have serious consequences to the garden. It is easily cured, but can have severe impact on plants if not addressed.

gal said: A sour mulch is one that is just anaerobic

==>>> that basically means .. because of the lack of oxygen.. that it is rotting.. rather than composting ... that sweet soil smell we all love ...

once spread.. it should dry.. and go away .... if not applied to thickly ... if such .. then you disturb it until it starts drying .. and normal composting processes take over ...

its akin to why swamps stink ...

in your pix.. the plantings are so dense.. i cant even figure out where you might have deep mulch ... maybe its wafting from the neighbors ..

ken