If I understand correctly, the soil (high water, low nutrients, slow decomposition) is what these plants are adapted for, and the acidity is an almost inevitable byproduct of those conditions, so the plant is adapted to that too, although pH 3 to 7 is actually quite a broad range! Thank you very much for this insight, and for the article that also describes this in detail. I'll try to find similar information for other species and continue the experiment. If I've got interesting findings, I'll post updates here.

How many are 'lots'? If it's not too many, maybe you can collect them and smash them, so they break down more easily, and at least they won't germinate.

I got it too. Just popped up. Bird love the berries, but I dare not eat them.

Must be slugs. I planted basil a couple of days ago and the next morning there was a big trail from my basil plants to my compost bin (in which I know they 'sleep'). They looked exactly like this: eaten and slimey.

It didn't show familiar to me, but searching for ulalo showed me a picture of the same animal on this page, on which the picture is captioned "Whitegrubs, Chafer grub (Schyzonycha spp.)", which is the larva of a scarab. Maybe that's helpful?

Larger at least. Not tastier per se.

I don't know. I only know it from hear-say. The main ingredient is (if I translate it right), a potassium salt of fatty acids. This also has a soapy texture, so it probably works in a similar way. I don't know if and why their stuff would be better than soft green or brown soap, but it could be.

The second one looks like a young red cabbage, judging by the color. The nerves are purple instead of white (like cauliflower), which rules out quite a couple of cultivars.

I don't know, but maybe the white stuff isn't part of the plant. Maybe it's some kind of spider, mite or caterpillar that made this. If so, someone might recognize the plant if you add a photo without fuzz.